Science 3

2. Which statement is true? a. When two elements form a series, they have the same composition. b. When two elements combine, there are always two compounds formed. c. When two elements combine, the first element is twice as much as the second. d. When two elements form a series of compounds, the ratio of the second element that combines with 1 g of the first element can be reduced into small whole numbers.3. Nitrogen and oxygen react to form dinitrogen oxide and nitrogen oxide. In dinitrogen oxide, there are 28.0 g of nitrogen and 16.0 g of oxygen. In nitrogen oxide, 14.0 g of nitrogen combine with 16.0 g oxygen. a. What is the ratio of the weights of nitrogen that combine with 16.0 g oxygen? b. How do these data illustrate the law of multiple proportions? Key to answers on page 22.Lesson 4. Writing Chemical Reactions and Balancing Chemical Equations The three fundamental chemical laws are the basis for writing chemical reactions.The conversion of substances to other substances during a chemical reaction is usuallyrepresented by a chemical equation. The chemical equation is very important because itprovides two types of information: the nature of reactants and products, and the relativenumber of each. This lesson is broken in two parts to make your learning easier.A. Writing Chemical Reactions Writing chemical reactions are important for chemists. It is an important languagethat translates the reactions into easy, readable and understandable sentence, which wecall the chemical equation. Word reactions are translated into symbols for easy reading. Bylooking at the chemical equations, the reader can easily interpret what transpired in thereaction. For example: The reaction of hydrogen and oxygen to give water is represented asfollows: 2H2 + O2 → 2H2O There are conventions and simple rules to follow in writing chemical equations. Theyare as follows: 1. As mentioned in Lesson 1, the starting material or substances called reactants - 13 -

are written on the left side and the resulting substances called products are written on the right side.2. An arrow (→) is used to represent the conversion of the reactants to products. This may literally mean “to yield” or “to form”. The plus sign (+) means “to react with” or “to combine with”.3. It is recommended that the states of the substances be indicated by placing the following symbols after the formula of the substance.Symbol Meaning (s) solid (l) liquid (g) gas (aq) (cr) aqueous Crystalline For example, the following equation is more descriptive of the reaction given earlier: 2H2(g) + O2(g) → 2H2O(l) The above reaction indicates that the water produced is in liquid form. Under other conditions, the water produced may be in gaseous state. 4. In a chemical reaction, the law of conservation of mass holds. A balanced equation conforms to this law. As mentioned in the previous lesson, the number of atoms of each kind on the left and right sides of the arrow must be equal.Try this:Write the chemical equation for this reaction: Two molecules of acetylene gas will react with 5 molecules of oxygen gas to produce4 molecules of carbon dioxide gas and two molecules of water vapor.Strategy: 1. Identify the reactants and products: C2H2 + O2 → CO2 + H2O 2. Indicate the states of the substances by placing their symbols on the right side of the substances C2H2(g) + O2(g) → CO2(g) + H2O(g) - 14 -

3. Affix the number of molecules as coefficients at the left side of the substances 2C2H2(g) + 5O2(g) → 4CO2(g) + 2H2O(g)4. Check the equation if it conforms with the Law of Conservation of Mass.Kind of atom Left side Right side C 2 x2=4 1x4=4 H 2 x2=4 2 x2=4 O 2 x 5 = 10 2(4) + 1(2) = 10 Your turn Write the chemical equation of the following chemical reactions. Check the equation if it conforms with the Law of Conservation of Mass. 1. Aqueous aluminum hydroxide decomposes to form solid aluminum oxide and liquid water. 2. One molecule of solid magnesium nitride reacts with six molecules of liquid water to form three moles of aqueous magnesium hydroxide and two moles of aqueous ammonia. 3. Two molecules of silver nitrate react with sulfuric acid to produce silver sulfate and two molecules of nitric acid. 4. Potassium nitrate decomposes to produce potassium nitrite and oxygen gas. Solution: A. 1. Al(OH)3(aq) → Al2O3(s) + H2O(l) 2. Mg3N2(s) + 6H2O(l) → 3Mg(OH)2(aq) + 2NH3(aq) 3. 2AgNO3 + H2SO4 → Ag2SO4 + 2HNO3 4. KNO3 → KNO2 + O2(g) B. 1 & 4 do not conform with the Law of Conservation of MassB. Balancing Equations Equations 1 & 4 in the previous exercise are examples of unbalanced equations.There is a way in which the atoms on the left and the right side of the arrow will be equal.This section will focus on the procedure of balancing equations by inspection. In general, a balanced chemical equation is written in two steps: 1. Write the formula and state or phase of the reactants and products. - 15 -

2. Balance the number of atoms of each kind by using coefficients. Write the coefficients on the left side of the substances. Note: The chemical formulas must not be changed. The subscripts must not be changed. Only the coefficients are to be adjusted.Example 1. Write the balanced equation for the reaction of solid magnesium with oxygen in air toproduce magnesium oxide. Step 1. Write the chemical equation Mg(s) + O2(g) → MgO(s) Step 2. Balance the number of atoms Mg(s) + O2(g) → MgO(s) Upon inspection, there are 2 atoms of oxygen in the left side, and only 1 atom of oxygen on the right side. Thus, we shall focus on balancing the oxygen atom on the right side by putting a coefficient 2 at the left side of MgO. Mg(s) + O2(g) → 2MgO(s) The oxygen atom is now balanced, but there is only 1 atom of Mg on the left side and two atoms on the right side. The next move is to put a coefficient 2 on the left side of Mg to balance the Mg atoms. 2Mg(s) + O2(g) → 2MgO(s) Step 3. Check the equation if it conforms with the Law of Conservation of Mass.Example 2. Let us take for example equation 1 of the previous exercise. Step 1. Write the formula Al(OH)3(aq) → Al2O3(s) + H2O(l) Step 2. Balance the number of atoms Al(OH)3(aq) → Al2O3(s) + H2O(l) Upon inspection, there are 2 atoms of aluminum on the right side, and only 1 atom of aluminum on the left side. Thus, we shall focus on balancing the aluminum - 16 -

atom on the left side by putting a coefficient 2 at the left side of Al(OH)3. 2Al(OH)3(aq) → Al2O3(s) + H2O(l) The aluminum atom is now balanced. On the left side of th equation, there are6 atoms of oxygen and 6 atoms of hydrogen. On the right side, there are 4 atoms ofoxygen and 2 atoms of hydrogen. It is suggested that we balance the hydrogen first.The subscript of hydrogen in water is 2. To make it 6, we need to put a coefficient 3on the left side of water. 2Al(OH)3(aq) → Al2O3(s) + 3H2O(l) The aluminum atom and the hydrogen atom are now balanced. Furtherinspection reveals that the oxygen atom is also balanced.Step 3. Check the equation if it conforms with the Law of Conservation of Mass.Your turnBalance the following equations:1. KNO3 → KNO2 + O2(g)2. H2(g) + I2(g) → HI(g)3. Al(s) + O2(g) → Al2O3(s)4. H3PO4(aq) + NH3(aq) → (NH4)3PO4(aq)Solution: 2KNO3 → 2KNO2 + O2(g) 1. H2(g) + I2(g) → 2HI(g) 2. 4Al(s) + 3O2(g) → 2Al2O3(s) 3. H3PO4(aq) + 3NH3(aq) → (NH4)3PO4(aq) 4. What you will do Self-Test 4.1A. Write the chemical equations of the following reactions: 1. Aqueous aluminum nitrate reacts with aqueous sodium hydroxide to form aqueous aluminum hydroxide and aqueous sodium nitrate. 2. Iron reacts with sulfuric acid to produce iron (III) sulfate and hydrogen gas. 3. Oxygen gas reacts with carbon sulfide to produce carbon dioxide and sulfur dioxide. - 17 -

B. Balance the following chemical reactions 1. Mg + N2 → Mg3N2 2. Cl2(g) + KBr(aq) → KCl(aq) + Br2(l) 3. C2H6 + O2 → CO2 + H2O Key to answers on page 23. Let’s Summarize This module is almost at its end. I hope you had a great time learning thefundamental chemical laws, writing reactions and balancing equations. To help youremember the key concepts discussed, let us go through them one more time.A. The three fundamental chemical laws are: 1. The Law of Conservation of Mass by Lavoisier Mass is neither created nor destroyed. In a chemical reaction, the number of atoms of each kind on the left and right sides of the arrow must be equal. 2. The Law of Definite Proportions by Proust A given compound always contains exactly the same proportion of elements by mass. That is why it is prohibited to change the subscripts of the formula in balancing equations. 3. The Law of Multiple Proportions When two elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers.B. Writing chemical reactions 1. Chemists use equations to describe the changes that substances undergo. The physical state of substances in the equation is shown by writing them at the right side of the substance: g for gas, l for liquid, s for solid and aq for water solution of the substances. 2. Reactants are the starting substances in a reaction. Products are the substances resulting from a reaction. Reactants are on the left of the equation and the - 18 -

products are on the right side of the equation. The arrow (→) means “to produce” or “to form”. The plus sign (+) means “to combine with” or “to react with”.C. Balancing equations 1. Write the chemical equations. Be sure your formulas are correctly written. 2. Balance the number of atoms of each kind by using coefficients. Write the coefficients on the left side of the substance. 3. Check the chemical equation if it conforms with the Law of Conservation of Mass.PosttestMultiple Choice. Choose the letter of the best answer. Write the chosen letter on aseparate sheet of paper.1. Which of the following is NOT an example of a chemical change?a. rusting iron c. cutting paperb. an apple ripening d. a piece of wood burning2. In a reaction in which hydrogen reacts with oxygen to produce water, which substancesare the reactants?a. hydrogen only c. both hydrogen and oxygenb. oxygen only d. water3. In a chemical equation, the symbol that takes the place of the word ‘yield’ is a(n)a. equal sign c. plus signb. coefficient d. arrow4. The word equation “magnesium reacts with chlorine to produce magnesium chloride” isrepresented by which of the following equations?a. Mg → Cl2 + MgCl2 c. MgCl2 + Mg → Cl2b. MgCl2 → Mg + Cl2 d. Mg + Cl2 → MgCl25. In a chemical reaction, what is the relationship between the total mass of the reactants and the total mass of the products? a. They must be equal. b. The mass of the products must be greater. c. The mass of the reactants must be greater. d. There is no general relationship between the two. - 19 -

6. In balancing a chemical equation, which of the following are you allowed to do?a. change subscripts c. change superscriptsb. write coefficients d. add new substances7. Which of the following symbols means a substance is in water solution?a. (aq) c. (w)b. (s) d. (l)8. What number should be written in front of O2 to balance the equation 4Al + O2 → Al2O3?a. 1 c. 3b. 2 d. 6For questions 9-15, refer to the figure below: NO9. From left to right, what are the chemical formulas for the substances represented in thefigure above?a. NO, N2, N2O c. N2, O2, NO2b. NO, O2, N2O d. NO, O2, NO210. What is the formula equation for the reaction in the figure?a. NO + O2 → NO2 c. N2 + O2 → NO2b. NO + O2 → N2O d. NO2 → NO + O211. In the figure, how many of each kind of atom is represented in the product?a. 1 nitrogen, 3 oxygen c. 2 nitrogen, 2 oxygenb. 1 nitrogen, 2 oxygen d. 2 nitrogen, 4 oxygen12. In the figure, how many of each kind of atom is represented in the reactants?a. 1 nitrogen, 3 oxygen c. 2 nitrogen, 2 oxygenb. 1 nitrogen, 2 oxygen d. 2 nitrogen, 4 oxygen13. In the figure, which of these statements is TRUE? a. The equation is balanced for both kinds of atoms. b. The equation is balanced for oxygen only. - 20 -

c. The equation is balanced for nitrogen atoms only.d. The equation is not balanced for either kind of atom.14. Assume that the number of oxygen molecules on the left side of the equation in the figure is held at one. What can you do to balance the equation? a. Nothing; it is already balanced. b. Change the molecule on the right by adding another oxygen atom. c. Add one NO molecule and one NO2 molecule to the equation. d. Add two NO molecules and two NO2 molecules to the equation.15. What is the balanced equation for the reaction as shown in the figure?a. 2NO + O2 → 2N2O c. NO + O2 → 2NO2b. 2NO + O2 → 2NO2 d. N2 + O2 → 2NO216. What scientific principle is reflected in a balanced equation? a. The law of conservation of mass c. The law of multiple proportions b. The law of conservation of atoms d. The law of definite proportions17. Why can’t you change the formula in order to balance a reaction? a. The number of atoms on the left should be equal to the atoms on the right of the arrow. b. The elements that combine have definite composition and fixed proportion of elements by mass. c. The elements have definite mass ratios. d. The molecule is indestructible.18. Which equation does NOT conform with the Law of conservation of Mass? a. 2Al(l) + 3BaO(s) → Al2O3(s) + 3Ba(l) b. CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) c. Cl2(g) + 2KBr(aq) → 2KCl(aq) + Br2(l) d. 2 Na(s) + H2O(l) → 2 NaOH(s) + H2(g)19. Which set of compounds illustrates the law of multiple proportions?a. CH4, CO, CCl4 c. NaCl, NaBr, NaIb. N2O, NO, NO2 d. HF, F2S, FCl320. Which statement is true? a. When two elements form a series, they have the same composition. b. When two elements combine, there are always two compounds formed. c. When two elements combine, the first element is twice as much as the second. d. When two elements form a series of compounds, the ratios of the second element that combines with 1 g of the first element can be reduced into small whole numbers.. Key to answers on page 23. - 21 -

Key to AnswersPretest1. b 6. d 11. c 16. b2. d 7. b 12. d 17. b3. b 8. c 13. c 18. b4. a 9. b 14. b 19. b5. c 10.d 15. a 20. dLesson 1Self-Test 1.11. The mass of the system is 250 g. (The mass of the reactant is equal to the mass of the product.)2. a does not conform with the Law of Conservation of Mass.3. Reactants on the left and Products on the right side of the arrow.Lesson 2Activity 2.11. 63 g of Na2. 0.71 g of hydrogen3. 45.2 g of oxygen, 11.3 g of carbonSelf-Test 2.11. b2. ClF33. a. 16 g b. 96g O2Lesson 3Self-Test 3.11. b2. d3. a. 2:1 b. The ratios are two whole numbers - 22 -

Lesson 4Self-Test 4.1A. 1. Al(NO3)3 + NaOH → Al(OH)3 + NaNO3 2. Fe + H2SO4 → Fe2(SO4)3 + H2 3. O2 + CS2 → CO2 + SO2B. 1. 3Mg + N2 → Mg3N2 2. Cl2 + 2KBr → 2KCl + Br2 3. 2C2H6 + 7O2 → 4CO2 + 6H2OPosttest1. c 6. b 11. b 16. a2. c 7. a 12. a 17. b3. d 8. c 13. d 18. d4. d 9. d 14. c 19. b5. a 10.a 15. b 20. dReferencesChang, R. (2002). Chemistry. (7th ed). USA:Mc-Graw Hill.Smoot, R., Smith, C., Richard, G. & Price, J. (1995). Merril Chemistry teacher wraparound edition. NY: Mc-Graw Hill.Padolina, M.C.D. (2000). Chemistry: Fundamental concepts of chemistry 1. UP Open University.Zumdahl, S.S. (1998). Chemical principles. (3rd ed). NYC: Houghton Mifflin Company. - 23 -

Module 14 The Chemical Bonds What this module is about Everything around us is made up of matter, from the very simple air that we breatheto the most complex of things that we deal with. You may wonder how we got all thesethings that make our life easy. This module is made for you to learn how scientists discovered atoms and howatoms combine and form simple to complex substances. Simple activities are provided tohelp you understand each lesson. Self-tests are also provided to help you check yourunderstanding and progress in each lesson.  Lesson 1 – Ionic and Covalent bonds  Lesson 2 – Polar and Nonpolar molecules  Lesson 3 – Intermolecular Forces of Attraction What you are expected to learn After going through this module, you are expected to: 1. Differentiate and describe the formation of ionic and covalent bonds. 2. Compare the properties of ionic and covalent compounds. 3. Differentiate between polar and nonpolar molecules 4. Classify molecules as polar or nonpolar. 5. Identify and differentiate the intermolecular forces of attraction. 6. Explain how these forces affect the compound’s interaction with other molecules How to learn from this module Here is a simple guide for you in going about this module. 1. Read and follow instructions very carefully.

2. Take the 10-item multiple choice test provided at the start of this module to determine how much you know about the lessons in this module3. Check your answers against the answer key provided at the last page of the module4. Perform all the activities provided in each lesson as these will help you have a better understanding of the topic.5. Take the self-tests at the end of each lesson for you to determine how much you remember about the lesson.6. Take the 10-item multiple–choice test at the end of the module. Good luck and have fun!What to do before (Pretest)Multiple Choice. Choose the letter that corresponds to the best answer. Write your choiceon a separate paper.1. It is a type of bond formed when atoms share electrons.a. Covalent bond c. Nonpolar bondb. Ionic bond d. Polar bond2. It refers to the ability of an atom to combine with other atomsa. atomic number c. ionic numberb. atomic mass d. oxidation number3. How many electrons are needed in the outer energy levels of most atoms for the atom tobe chemically stable?a. 2 c. 6b. 4 d. 84. What kind of chemical bond is formed when electrons are gained and lost from atoms?a. ionic c. magneticb. covalent d. metallic5. How come noble gases do not form compounds readily? a. They have no electrons. b. They have empty outer energy levels. c. They have 7 electrons in their outer energy levels. d. Their outer energy levels are completely filled.6. It is the force that holds the atoms together in a compound.a. chemical bond c. chemical formulab. chemical equation d. chemical symbol -2-

7. It refers to a charged atom. c. compound a. element d. molecule b. ion8. Most of the matter around you are in the form of _____.a. elements c. atomsb. compounds d. ions9. A molecule that has oppositely charged ends is called ____.a. covalent c. nonpolarb. ionic d. polar10. Which of the following compounds can form H-bond with water?a. NH3 c. CaOb. HCl d. CH4 Key to answers on page 21.Lesson 1. Ionic and Covalent Bonds What you will do Activity 1.1 The Mystery of Table Salt 1. Get a pinch or two of table salt (NaCl). 2. Place this in a very hot frying pan. Observe what happens after continuously heating it for 15 minutes (be careful not to hold it with your bare hands). 3. Place the same amount of table salt directly on red-hot piece of charcoal. Observe what happens. Is there a difference between the pinch of salt placed in a hot frying fan and the one directly placed on the red-hot charcoal? 4. Sprinkle the same amount of salt in a glassful of water. Observe what happens. What do your observations say regarding the properties of the bond that holds sodium and chlorine together in this compound? Try to compare this with an amount of rubbing alcohol on your skin. Which of the two compounds is being held by a stronger bond? -3-

What you will do Activity 1.2 Electrical Conductivity of SolutionsPurpose: This demonstration provides experimental evidence on the nature of ionic and molecular substances in solution and as a molten ionic solid. Its major purpose is to show that ionic solids conduct electric current both in solution and when fused, whereas molecular solids do not.Materials:  Electrical conductivity apparatus (commercial or home-made)  6-8 glasses, 50 mL, or 2 oz. wide-mouth bottles  Solid sodium chloride (table salt), NaCl, and sucrose, C12H22O11 (common table sugar)  Solid silver nitrate, AgNO3  2 or 3 small crucibles or brown bottles  Ring stand, ring, triangle  0.1 M solutions of NaCl and sucrose (5.6 g NaCl/100 mL solution and 3.4 g sucrose/100 mL solution)Safety: If the conductivity tester used is powered by a 120-V source, then use caution to prevent electric shock. The substances used are safe and do not require special handling except for the silver nitrate, which is both toxic and caustic. Handle the silver nitrate with care, particularly when it is fused since it is also an oxidizer. Solutions may be safely disposed by flushing them down the drain with water. The solid NaCl and sugar may be used for all demonstrations and then disposed in the trash. Keep the crucible with silver nitrate in a dark bottle for later use. It may be reused many times.Procedure: 1. Half-fill a 50-mL glass with solid NaCl and a second 50-mL glass with solid sucrose. Test the electrical conductivity of the solid NaCl with the tester (light bulb remains dark). Clean the electrodes and then test the solid sucrose (light bulb remains dark). Record your observation. 2. Half-fill two 50-mL glasses with the two solutions and a third with distilled water. First, test the electrical conductivity of the distilled water. Then test the electrical conductivity of each of the two solutions in turn. Record your observation. 3. Half-fill a small crucible with silver nitrate. Place the crucible on a triangle supported on an iron ring mounted on a ring stand. Heat the crucible with an alcohol lamp until the silver nitrate is melted. Carefully test the electrical conductivity of the melted silver nitrate. Record your observation. -4-

Chemical Bonding: Ionic and Covalent There are almost 118 elements listed in the periodic table, but there are obviouslymore substances in nature than 118 pure elements. This is attributed to the capacity of theatoms to combine and react with other atoms to form new compounds. Every compoundformed is unique both chemically and physically from its parent atoms. An example of this is the reaction between the silver-colored metal sodium and thegreenish-colored gas chlorine that forms the compound sodium chloride. Sodium metal is avery reactive metal. It reacts violently with water and it produces flame once it gets wet.The element chlorine is a poisonous gas used as a weapon in World War I. When thesedangerous substances (sodium metal and chlorine gas) chemically bond together, they formthe compound sodium chloride – the common table salt which is so safe that we even eat iteveryday! +sodium metal chlorine gas table salt The concept of bonding was originally explained by the American chemist GilbertNewton Lewis. He proposed that chemical bonds are formed between atoms becauseelectrons from the atoms interact with each other. Lewis had observed that many elementsare most stable when they contained eight electrons in their valence shell (outermost shell)like that of the noble gases. This condition is attained by atoms either by transferring orsharing the valence electrons. These two processes of forming the two main types ofchemical bonding are ionic and covalent bonding. Ionic bonding involves the combination of ions of opposite charges. Cations arepositively-charged atoms which are formed when an atom loses electron/s. The chargedepends on the number of electrons the atom lost. On the other hand, atom/s that gainelectron/s become negatively charged as the number of electrons exceeds the number ofprotons and are therefore called anions. The compounds formed are called ioniccompounds. As shown in the figure on the next page, in ionic bonding electrons are completelytransferred from one atom to another. In the process of either losing or gaining negativelycharged electrons, the reacting atoms form ions. The oppositely charged ions are attractedto each other by electrostatic forces which are the basis for ionic bond formation. Noticethat when sodium loses its one valence electron it gets smaller in size, while chlorine growslarger when it gains an additional valence electron. This is typical of the relative sizes ofions to atoms. Positive ions tend to be smaller than their parent atoms while negative ionstend to be larger than their parent atoms. After the reaction takes place, the charged Na+ -5-

and Cl- ions are held together by sodium (on the left)electrostatic forces, thus forming an loses one valenceionic bond. Ionic compounds share electron to chlorinemany features in common: (on the right),  Ionic bonds form between resulting in metals and nonmetals. a positively charged  In naming simple ionic sodium ion (left) and compounds, the metal is a negatively charged always given first, the chlorine ion (right). nonmetal second (ie. sodium chloride). the reaction of sodium and chlorine  Ionic compounds dissolve easily in water and other polar solvents.  In solution, ionic compounds easily conduct electricity.  Ionic compounds tend to form crystalline solids with high melting temperatures.What is a Covalent Compound? I'm glad you asked! A covalent compound is a compound in which the atoms that arebonded share electrons rather than transfer electrons from one to the other. While ioniccompounds are usually formed when metals bond to nonmetals, covalent compounds areformed when two nonmetals bond to each other. The big question that students frequently ask is: \"Why do elements share electrons?After all, wouldn't electrons rather grab electrons outright? That's what happens when ioniccompounds are formed.\" The reason why nonmetals have to share electrons among themselves has to do withelectronegativity. Recall that electronegativity is a measure of how much an element pullselectrons away from other elements it is bonded to. Metals generally have very lowelectronegativities (they don't want to grab electrons) while nonmetals have highelectronegativities (they really want to grab electrons). The reason for this trend is the octetrule, which says that all elements want to have the same number of electrons as the nearestnoble gas, because noble gases are unusually stable. When metals bond to nonmetals,ionic compounds are formed because the metal atoms don't want electrons and easily givethem to nonmetals that want electrons. It is a different story when two nonmetals bond with each other. Instead of havingone element giving electrons to another, we run into a case where we have two elementshaving roughly the same electronegativity. Thus, neither element can steal electrons fromthe other. As a result, if either of them is going to be like the nearest noble gas, they'll haveto share electrons rather than transfer them. -6-

An example of this case is shown below where two chlorine atoms share theirvalence electrons. Chlorine atoms have seven electrons each and will be a lot more stablewith eight electrons in the outer shell. Single chlorine atoms just do not exist because theycome in pairs to share a pair of electrons. The shared pair of electrons make a bondbetween the atoms. In Lewis structures, the outside electrons are shown with dots andcovalent bonds are shown by bars. This covalent bond between chlorine atoms is one of the most covalent bondsknown. Why? A covalent bond is the sharing of a pair of electrons. The two atoms oneither side of the bond are exactly the same, so the amount of \"pull\" of each atom on theelectrons is the same, and the electrons are shared equally.What are the Properties of Covalent Compounds? Covalent compounds have the following properties (keep in mind that these are onlygeneral properties, and that there are always exceptions to every rule):1. Covalent compounds generally have much lower melting and boiling points than ionic compounds. As you may recall, ionic compounds have very high melting and boiling points because it takes a lot of energy for all of the + and - charges which make up the crystal to get pulled apart from each other. Essentially, when we have an ionic compound, we need to break all of the ionic bonds in order to make it melt. On the other hand, when we have covalent compounds we don't need to break any bonds at all. This is because covalent compounds form distinct molecules, in which the atoms are bound tightly to one another. Unlike in ionic compounds, these molecules don't interact with each other much (except through relatively weak forces called \"intermolecular forces\"), making them very easy to pull apart from each other. Since they're easy to separate, covalent compounds have low melting and boiling points.2. Covalent compounds are soft and squishy (compared to ionic compounds). The reason for this is similar to the reason that covalent compounds have low melting and boiling points. When you hit an ionic compound with something, it feels very hard because all of the ionic bonds which hold the crystal together tend to make it very inflexible and hard to move. On the other hand, covalent compounds have molecules which easily move around each other because there are no bonds between them. As a result, covalent compounds are more likely to be flexible than -7-

hard. Think of it like this: Ionic compounds are like giant Lego sculptures. If you hit a Lego sculpture with your fist, it feels hard because all of the Legos are stuck very tightly to one another. Covalent compounds are more like those plastic ball pits found in playpens for little kids. While the balls themselves are held together very tightly (just like covalent molecules are held together tightly), the balls aren't really stuck to each other at all. As a result, when little kids jump into the ball pits, they sink in instead of bouncing off.3. Covalent compounds tend to be more flammable than ionic compounds. Things burn because they contain carbon and hydrogen atoms that can react to form carbon dioxide and water when heated with oxygen gas (that's the definition of a combustion reaction). Since carbon and hydrogen have very similar electronegativities, they are mostly found together in covalent compounds. As a result, more covalent compounds than ionic compounds are flammable. There are a couple of exceptions to this rule. The first is with covalent compounds that contain neither carbon nor hydrogen. These tend not to burn, and if they do, they burn by mechanisms other than the classic combustion reaction. The other exception comes with ionic compounds referred to as \"organic salts\". These organic salts are ionic compounds in which the anion is basically a big covalent molecule containing carbon and hydrogen with just a very small ionic section. As a result, they burn even though they're technically ionic compounds.4. Covalent compounds don't conduct electricity in water. Electricity is conducted in water from the movement of ions from one place to the other. These ions are the charge carriers which allow water to conduct electricity. Since there are no ions in a covalent compound, they don't conduct electricity in water.5. Covalent compounds aren't usually soluble in water. There's a saying that, \"Like dissolves like\". This means that compounds tend to dissolve in other compounds that have similar properties (particularly polarity). Since water is a polar solvent and most covalent compounds are fairly nonpolar, many covalent compounds don't dissolve in water. Of course, this is a generalization and not set in stone - there are many covalent compounds that dissolve quite well in water. However, the majority of them don't because of this rule.What you will doSelf-Test 1.1 -8-

Multiple Choice. Choose the letter that corresponds to the best answer. Write your choiceon a separate paper.1. What is formed when an atom loses electron/s?a. anion c. neutral atomb. cation d. none of the above2. What do you call the electrons which are transferred or shared by an atom?a. valence electrons c. excited electronsb. inner- shelled electrons d. electrons in the ground state3. Which is a stronger bond? c. single bond a. covalent d. double bond b. ionic4. What rule or law is followed by atoms in attaining eight electrons in the outermost shell?a. Law of definite proportion c. Law of Multiple proportionb. Law of conservation of matter d. Octet rule5. Which compound has the higher boiling point/melting point?a. alcohol c. oilb. table salt d. wax Key to answers on page 22. If you scored 3 or more out of 5 –CONGRATULATIONS!You may now proceed to the next lesson. If you scored below 3, you need to go back andread the lesson again!Lesson 2. Polar and Nonpolar Bonds What you will do Activity 2.1 Why is it that oil and water do not mix? In your school, do the boys and girls mix? Probably not and that is not because thegirls don't like the boys (usually), or because the boys don't like the girls. It's just that young -9-

girls like spending time with other young girls more than with young boys. Boys and girlstend to like to do different things and talk about different things when they are young. Imagine you are a girl going out of the classroom for recess. You look around. Yousee a boy or two, and a girl or two. Naturally you go over to the girls to talk. Later, anothergirl comes out. She, too, goes over to the girls to talk. After a while, after every child isoutside the classroom you have batches of boys and batches of girls all over the place, butnot many areas where boys and girls are together. The same thing happens with oil and water. Oil is made of molecules (which are likevery small, sticky rubber balls). So is water. But water molecules are not the same as oilmolecules. Most importantly, while all molecules like to stick to each other, oil moleculeslike to stick to other oil molecules more than they like to stick to water molecules. Samewith the water: water molecules like to stick to oil molecules, but they like to stick to otherwater molecules even more. So, if you pour some water into oil, the water molecules coming in see oil moleculesand (at first only a few) water molecules. Naturally they prefer to join the other watermolecules. Thus, you get particles of water and particles of oil, but nowhere do you find thetwo kinds of molecules mixed up together. It turns out that oil is lighter than water, so theparticles of oil tend to float up on top of the water, and join together into a big oil slick. If youget enough oil, you get a thick layer of it on top of the water. You can sort of mix up the oiland water by shaking the jar, but you will only break up the layer into smaller particles, andthey will come back together again quickly because of the lightness of oil. Now, if you wereon the Space Shuttle, the particles wouldn't form a thick layer, they'd just stay all jumbledup. The oil and water wouldn't mix! You can force oil and water to mix. What you need is a type of molecule that boththe water and the oil like to stick to more than they like to stick to each other. Such amolecule is called an emulsifier, or, more simply, a soap. When you get a soap molecule,the water and the oil stick to it, and then the oil and water mix. A lot of things can be used as emulsifiers. Soap is one of them. If you get greaseon your hands, plain water won't wash it off -- the grease won't mix with the water and comeoff. But if you put soap on your hands, the grease will mix with the water and come off. An egg yolk is another emulsifier. If you mix salad oil and vinegar (which is mostlywater), and then put some eggs in, the oil and vinegar will mix -- you get mayonnaise. Youcan make mayonnaise with oil, vinegar, and eggs in your blender at home. Water is a polar molecule which means that it has a negatively charged end and apositively charged end. So water molecules attract each other. They also attract otherpolar molecules. Oil is NOT a polar molecule-it doesn't have a separation of charge. Sowater and oil aren't attracted to each other. Just remember-like dissolves like. - 10 -

Polar Covalent Compounds Bonding between nonmetals consists of two electrons shared between two atoms. Incovalent bonding, the two electrons shared by the atoms are attracted to the nucleus of bothatoms. Neither atom completely loses or gains electrons as in ionic bonding. There are two types of covalent bonding: 1. Nonpolar bonding with an equal sharing of electrons. 2. Polar bonding with an unequal sharing of electrons. The number of shared electrons depends on the number of electrons needed to complete the octet. POLAR BONDING is the result when two different nonmetals unequally shareelectrons between them. One well known exception to the identical atom rule is thecombination of carbon and hydrogen in all organic compounds. The nonmetal closer to fluorine in the Periodic Table has a greater tendency to keepits own electron and also draw away the other atom's electron. It is NOT completelysuccessful. As a result only partial charges are established. One atom becomes partiallypositive since it has lost control of its electron most of the time. The other atom becomespartially negative since it gains electron most of the time. Water, the most universal compound on earth, has the property of being a polar molecule. Thus, the physical and chemical properties of the compound are fairly unique. Hydrogen Oxide or water forms a polar covalent molecule. The graphic on the left shows that oxygen has 6 electrons in the outer shell. Hydrogen has one electron in its outer energy shell. Since 8 electrons are needed for an octet, they share the electrons. However, oxygen gets an unequal share of the two electrons from both hydrogen atoms. Again, the electrons are still shared (not transferred as in ionic bonding), and the sharing is unequal. The electronsspend more of the time closer to oxygen. As a result, the oxygen acquires a \"partial\"negative charge. At the same time, since hydrogen loses the electron most - but not all ofthe time, it acquires a \"partial\" charge. The partial charge is denoted with a small Greeksymbol for delta. Water is a polar molecule with positive charges on one side and negativecharges on the other. NONPOLAR BONDING results when two identical nonmetals equally shareelectrons between them. One well known exception to the identical atom rule is thecombination of carbon and hydrogen in all organic compounds. A nonpolar molecule is one - 11 -

where the electrons are distributed more symmetrically. Thus it does not have anabundance of charges at the opposite sides. The charges all cancel each other out. Iodine forms a diatomic nonpolar covalent molecule. The graphic on the top left shows that iodine has 7 electrons in the outer shell. Since 8 electrons are needed for an octet, two iodine atoms EQUALLY share 2 electrons. Molecules of oxygen, which are present in about 20% concentration in air, are also covalent molecules. (See the graphic at the left). There are 6 electrons in the outer shell, therefore, 2 electrons are needed to complete the octet. The two oxygen atoms share a total of four electrons in two separate bonds called double bonds. The two oxygen atoms equally share the four electrons.Comparison of Ionic, Polar, and Nonpolar Bonds Whereas nonpolar bonding involves the equal sharing of electrons between identicalnonmetal atoms, POLAR BONDING is the unequal sharing of electrons between twodifferent nonmetal atoms. A proper understanding of polar bonding is gained by viewing thetypes of bonding on a continuum as in the diagram below. Ionic bonding is on one extremewith a complete transfer of electrons forming charged ions. Nonpolar covalent bonding with equal sharing of electrons is at the other extreme.Somewhere in the middle but favoring the covalent side is polar bonding with unequalsharing of electrons and partial but incomplete transfer of electrons. - 12 -

Rule: Polar molecules will mix to form solutions and nonpolar molecules will also mix toform solutions, but a polar and nonpolar combination will not form a solution. Water is a polar molecule and oil is a nonpolar molecule. Thus they won't form asolution. On the other hand, since alcohol is a polar molecule, it will form a solution withwater. Before going on, try answering the following: What you will do Self-Test 2.1Multiple Choice. Choose the letter that corresponds to the best answer. Write your choiceon a separate paper.1. Which of the following pairs will form polar covalent bond? a. Cl and Cl b. H and Cl c. H and H2. Where will the partial positive end be found on the bond that will be formed in number 1? a. H b. Cl - 13 -

3. Which of the following pairs will be soluble with one another? a. Br2 and CCl4 b. Oil and water c. H2O and CCl4For numbers 4 and 5, refer to the following choices: a. polar covalent b. nonpolar covalent c. none of the above4. What kind of bond is formed by two identical atoms?5. It is the kind of bond formed by atoms with different electronegativities. Key to answers on page 22. If you scored 3 or more out of 5 –CONGRATULATIONS!You may now proceed to the next lesson. If you scored below 3, you need to go back andread the lesson again!Lesson 3. Intermolecular Forces of Attraction What you will do Activity 3.1 How would you explain the difference in the boiling points of water and rubbingalcohol? The physical properties of substances like melting point, boiling point, vaporpressure, evaporation, viscosity, surface tension, and solubility are related to the strength ofattractive forces between molecules. These attractive forces are called IntermolecularForces. This is the force responsible for why molecules stick together. The amount of\"stick togetherness\" is important in the interpretation of the various properties listed above. The three types of intermolecular forces are Dispersion Forces, Dipole-dipoleinteractions and Hydrogen bonding. Dispersion forces, also known as London Forces,(named after Fritz London who first described these forces theoretically 1930) is consideredas the weakest intermolecular force. Most of the intermolecular forces are identical tobonding between atoms in a single molecule. - 14 -

Dipole Forces Polar covalent molecules are sometimesdescribed as \"dipoles\", meaning that the moleculehas two \"poles\". One end (pole) of the molecule hasa partial positive charge while the other end has apartial negative charge. The molecules will orientatethemselves so that the opposite charges attract andthe principle operates effectively. In the example on the right, hydrochloric acid isa polar molecule with the partial positive charge onthe hydrogen and the partial negative charge on thechlorine. A network of partial + and - charges attractmolecules to each other. Dipole-dipole interactions are stronger intermolecular forces than Dispersion forces.They occur between molecules that have permanent net dipoles (polar molecules). Forexample, dipole-dipole interactions occur between SCl2 molecules, PCl3 molecules andCH3Cl molecules. If the permanent net dipole within the polar molecules results from acovalent bond between a hydrogen atom and either fluorine, oxygen or nitrogen, theresulting intermolecular force is referred to as a hydrogen bond (see below). The partialpositive charge on one molecule is electrostatically attracted to the partial negative chargeon a neighboring molecule.Hydrogen Bonding The hydrogen bond is really a special case of dipoleforces. A hydrogen bond is the attractive force betweenthe hydrogen attached to an electronegative atom of onemolecule and an electronegative atom of a differentmolecule. Usually the electronegative atom is oxygen,nitrogen, or fluorine. To recognize the possibility ofhydrogen bonding, examine the Lewis structure of themolecule. The electronegative atom must have one ormore unshared electron pairs as in the case of oxygen andnitrogen, and has a negative partial charge. Thehydrogen, which has a partial positive charge, tries to findanother atom of oxygen or nitrogen with excess electronsto share and is attracted to the partial negative charge.This forms the basis for the hydrogen bond. In the figure on the left, the hydrogen is partially positive and is attracted to thepartially negative charge on the oxygen. Because oxygen has two lone pairs, two differenthydrogen bonds can be made to each oxygen. H bonds are stronger intermolecular forcesthan either dispersion forces or dipole-dipole interactions. - 15 -

This is a very specific bond as indicated. Some combinations which are nothydrogen bonds include hydrogen to another hydrogen or hydrogen to a carbon.Induced Dipole Forces (Dispersion Forces) Forces between essentially nonpolar moleculesare the weakest of all intermolecular forces.\"Temporary dipoles\" are formed by the shifting ofelectron clouds within molecules. These temporarydipoles attract or repel the electron clouds of nearbynonpolar molecules. The temporary dipoles may exist for only afraction of a second but a force of attraction also existfor that fraction of time. The strength of induced dipoleforces depends on how easily electron clouds can bedistorted. Large atoms or molecules with manyelectrons far removed from the nucleus are more easilydistorted. Induced dipole or dispersion forces are very weak forces of attraction betweenmolecules because this interaction is the result of the following:  momentary dipoles occurring due to uneven electron distributions in neighbouring molecules as they approach one another  the weak residual attraction of the nuclei in one molecule for the electrons in a neighbouring molecule. The more electrons that are present in the molecule, the stronger the dispersionforces will be. Dispersion forces are the only type of intermolecular force operating betweennonpolar molecules. For example, dispersion forces operate between hydrogen (H2)molecules, chlorine (Cl2) molecules, carbon dioxide (CO2) molecules, dinitrogen tetroxide(N2O4) molecules and methane (CH4) molecules.Relative Strength of Intermolecular Forces Intermolecular forces (dispersion forces, dipole-dipole interactions and hydrogenbonds) are much weaker than intramolecular forces (covalent bonds, ionic bonds or metallicbonds). Dispersion forces are the weakest intermolecular force (one hundredth-onethousandth the strength of a covalent bond). On the other hand, hydrogen bonds are thestrongest intermolecular force (about one-tenth the strength of a covalent bond). (dispersion forces < dipole-dipole interactions < hydrogen bonds) - 16 -

Effect of Intermolecular Forces on Melting and Boiling Points of Molecular CovalentSubstances Since melting or boiling results from a progressive weakening of the attractive forcesbetween the covalent molecules, the stronger the intermolecular force is, the more energy isrequired to melt the solid or boil the liquid. If only dispersion forces are present, then themore electrons the molecule has (and consequentlythe more mass it has) the stronger the dispersionforces will be, and the higher the melting and boilingpoints will be. Consider the hydrides of Group IV, allof which are nonpolar molecules; thus, onlydispersion forces act between the molecules. CH4(molecular mass ~ 16), SiH4 (molecular mass ~ 32),GeH4 (molecular mass ~ 77) and SnH4 (molecularmass ~ 123) can all be considered nonpolar covalentmolecules. As the mass of the molecules increases, so does the strength of the dispersion forceacting between the molecules. This implies that more energy is required to weaken theattraction between the molecules resulting in higher boiling points. If a covalent molecule has a permanent netdipole then the force of attraction between thesemolecules will be stronger than if only dispersionforces were present between the molecules. As aconsequence, this substance will have a highermelting or boiling point than similar molecules that arenonpolar in nature. Consider the boiling points of thehydrides of Group VII elements. All of the moleculesHF (molecular mass ~ 20), HCl (molecular mass ~37), HBr (molecular mass ~ 81) and HI (molecularmass ~ 128) are polar, the hydrogen atom having apartial positive charge (H) and the halogen atomhaving a partial negative charge(F, Cl, Br, I). As a consequence, the stronger dipole-interactions acting between the hydridemolecules of Group VII elements results in higher boiling points than for the hydrides ofGroup IV elements as seen in the previous page. Usually, as the molecular mass increases, the boiling point of the hydrides increases.HF is an exception to this rule because of the stronger force of attraction between HFmolecules resulting from hydrogen bonds acting between the HF molecules. Weakerdipole-dipole interactions act between the molecules of HCl, HBr and HI. So HF has ahigher boiling point than the other molecules in this series. - 17 -

Effect of Intermolecular Forces on Solubility In general like dissolves like. Specifically  nonpolar solutes dissolve in nonpolar solvents. Paraffin wax (C30H62) is a nonpolar solute that will dissolve in nonpolar solvents like oil, hexane (C6H14) or carbon tetrachloride (CCl4). Paraffin wax will NOT dissolve in polar solvents such as water (H2O) or ethanol (ethyl alcohol, C2H5OH).  polar solutes such as glucose (C6H12O6) will dissolve in polar solvents such as water (H2O) or ethanol (ethyl alcohol, C2H5OH). This is so because the partially positively charged atom of the solute molecule is attracted to the partially negatively charged atom of the solvent molecule, and the partially negatively charged atom of the solute molecule is attracted to the partially positively charged atom of the solvent molecule. Glucose will NOT dissolve in nonpolar solvents such as oil, hexane (C6H14) or carbon tetrachloride (CCl4).  Ionic solutes such as sodium chloride (NaCl) will generally dissolve in polar solvents but not in nonpolar solvents, since the positive ion is attracted to the partially negatively charged atom in the polar solvent molecule, and the negative ion of the solute is attracted to the partially positively charged atom on the solvent molecule. Before going on, try answering the following: What you will do Self-Test 3.1Multiple Choice. Choose the letter that corresponds to the best answer. Write your choiceon a separate paper.1. The boiling point of CH4 is much lower than that of HF. This is explained by the a. hydrogen bonding in HF b. ion-dipole interaction in CH4 c. polarity of CH42. What causes the high surface tension of water? a. hydrogen bonding b. dipole-dipole c. dispersion forces3. Which is most likely to have the strongest intermolecular forces? a. solid b. liquid c. gas - 18 -

For nos. 4 and 5, refer to the following choices: a. hydrogen bond b. dipole-dipole c. dispersion forcesWhat intermolecular force of attraction is present in each of the following?4. water5. carbon dioxide Key to answers on page 22. If you scored 3 or more out of 5 –CONGRATULATIONS!If you scored below 3, you need to go back and read the lesson again! Let's Summarize1. There are two types of bond that can be produced when atoms combine. These are: a. Ionic bond This kind of bond is formed by the electrostatic attraction between a cation (metal) and an anion (nonmetal). The compound formed is called ionic compound. Ionic compounds have higher melting and boiling points compared to covalent compounds. They easily ionize in water. b. Covalent bond The bond is formed when nonmetals share their valence electrons (electrons in the outermost shell) with another nonmetal. The compound formed is called covalent compound and it may be diatomic or polyatomic in nature. Generally, covalent bonds are weaker than ionic compounds, and they have lower boiling and melting points, too.2. Classification of Covalent Bonds a. Polar covalent bond is formed when there is unsymmetrical sharing of electron cloud. It is formed by nonmetals of different electronegativity. This bond is characterized by the presence of partial positive and negative ends. The partial positive end is found on the atom with the lower electronegativity while partial negative end is on the more electronegative atom. b. Nonpolar covalent bond is characterized by the symmetrical distribution of electron cloud around the combining atoms. Identical atoms form this kind of - 19 -

bond. c. The rule of thumb that “like dissolves like” is best explained by this concept on polarity.3. Three types of force can operate between covalent molecules: a. Dispersion Forces is also known as London Forces (named after Fritz London who first described these forces theoretically in 1930) or as Weak Intermolecular Forces or as van der Waal's Forces (named after the person who contributed to our understanding of non-ideal gas behavior). b. Dipole-dipole interactions c. Hydrogen bonds4. Relative strength of Intermolecular Forces: a. Intermolecular forces (dispersion forces, dipole-dipole interactions and hydrogen bonds) are much weaker than intramolecular forces (covalent bonds, ionic bonds or metallic bonds) b. Dispersion forces are the weakest intermolecular force (one hundredth-one thousandth the strength of a covalent bond), hydrogen bonds are the strongest intermolecular force (about one-tenth the strength of a covalent bond). c. dispersion forces < dipole-dipole interactions < hydrogen bondsPosttestMultiple Choice. Choose the letter that corresponds to the best answer. Write your choiceon a separate paper.1. Solute is most likely to be highly soluble in a solvent if the solute is _____ and thesolvent is ______.a. ionic, polar c. polar, polarb. nonpolar, ionic d. nonpolar, ionic2. Molecular iodine would be most soluble in a. Water b. Carbon tetrachloride c. Ethanol and water3. The concept of “like dissolves like” is illustrated by which of the following? a. NaCl (s) is more soluble in CCl4 than in water. b. I2 (s) is more soluble in CCl4 than in water. c. CCl4 is soluble in water - 20 -

4. Which one of the following molecules would be most polar? a. H2 b. HF c. HCl5. Which of the following bond types is the strongest? a. Polar b. Nonpolar c. IonicFor numbers 6-8, refer to the following choices: a. covalent bond b. ionic bond6. The bond formed by Ca2+ and O2+7. The bond formed by two oxygen atoms8. The bond present in table saltFor numbers 9 to 10, refer to the following: a. BaCl2 b. CO2 c. NH39. Which of the given compounds has the highest boiling point?10. Which one will not dissolve in a polar solvent? Key to answers on page 22.If you scored 7 or more out of 10 – Congratulations! You may now proceed to the nextmodule. If you scored below 7, you need to go back and read the module again!Key to AnswersPretest 6. a 7. b 1. a 8. b 2. d 9. d 3. d 10. a 4. a 5. d - 21 -

Lesson 1 Lesson 2 Lesson 3 Self-Test 1.1 Self-Test 2.1 Self-Test 3.1 1. b 1. b 1. a 2. a 2. a 2. a 3. b 3. a 3. a 4. c 4. b 4. a 5. b 5. a 5. cPosttest 6. b 7. a 1. c 8. b 2. b 9. a 3. b 10. b 4. b 5. cReferencesBooks:Chang, R. (2005). Chemistry. Arizona: McGrawHill.Redmore, F. (1989). Fundamentals of chemistry. San Diego, CA: Academic Press.Electronic Sources:http://www.sparknotes.com/chemistry/bonding/covalent/summary.htmlhttp://www.accessexcellence.orghttp://www.ausetute.com.au/intermol.html - 22 -

Module 15 Changes That Matter Undergoes What this module is about The mango turns yellow as it ripens, rust appears on the hinges of the door, andleftover food produces a foul smell. These are just some of the changes we find everyday.As a young curious scientist, you wanted to know why and how these natural events occur.Is it possible for you to control them? In this module, we will present several phase and chemical changes that occur in ourhomes, in the environment, outside our homes, and in some industries. We will cover thefollowing lessons:  Lesson 1 – Changing Phases  Lesson 2 – When Does A Chemical Change Occur?  Lesson 3 – Types of Chemical Changes  Lesson 4 – Chemical Changes Around Us This module is probably the most exciting one that you will read. Ready? What you are expected to learn After reading this module, you must be able to accomplish the following: 1. differentiate phase changes from chemical changes; 2. explain how phase changes occur; 3. cite some uses of phase changes; 4. determine the evidences of chemical changes; 5. differentiate the types of chemical changes; 6. describe some changes in the human body; 7. describe some changes in the environment; 8. explain the application of phase changes and chemical changes at home, in the community and in industries; and 9. state how these changes help improve the quality of life.

How to learn from this module Here are some tips for you to remember to get the most out of this module. 1. Assign a quiet place in the house for your place of study. It should have good reading light and make sure that your learning modules, ball pens, and papers are within easy reach. 2. Assign a daily study time. You probably have a lot of things to do throughout the day, but set aside a fixed study time. For example, you are most mentally alert every afternoon and you choose to start studying the module at 3:00 pm up to 5:00 pm. Do this everyday. 3. Conduct the activities described in each lesson. These activities will help you understand the concepts presented. 4. Ask yourself questions about each topic. You may also write down your questions. Then after reading, check if these questions were answered. 5. Read actively. After reading one or two paragraphs, think of the main idea being presented. Think also of how this idea relate to your environment. 6. Answer the self-tests found at the end of each lesson. They will tell you whether you have learned enough from the lesson or not. 7. Go beyond what is written in this module. Do research. The tips here are given to improve your concentration and to help you successfullyfinish this module. You may also have your own ways of improving your reading andcomprehension.What to do before (Pretest)Multiple Choice. Choose the letter of the best answer. Write the chosen letter on aseparate sheet of paper.1. Which is a chemical reaction? c. boiling of water a. melting of ice d. drying of clothes b. frying of egg2. Which condition will allow condensation (gas to liquid change)? a. high temperature and high pressure b. high temperature and low pressure c. low temperature and high pressure d. low temperature and low pressure -2-

3. The change from solid to gas, which does not pass through the liquid phase, is known asa. freezing c. sublimationb. melting d. vaporization4. Which is an evidence of chemical change?a. formation of new shape c. increase of temperatureb. drastic change of size d. appearance of new substance5. What do carbohydrates provide for our body?a. oil c. oxygenb. water d. energy6. In a recipe, which of these words implies a chemical change?a. bake c. cubeb. chill d. mash7. Which of these represents a synthesis chemical reaction?a. X + Y → XY c. XY + Z → X + ZYb. XY → X + Y d. XY + ZW → XW + ZY8. What type of chemical change is oxidation?a. composition c. single replacementb. decomposition d. double displacement9. What type of chemical change is the extraction of Aluminum metal?a. composition c. single replacementb. decomposition d. double displacement10. Which of these changes is NOT considered dangerous?a. curing of meat c. blackening of lungsb. burning of garbage d. leaching of fertilizer Key to answers on page 22.Lesson 1. Changing Phases There are three phases of matter, namely:solid, liquid, and gas. These three phases ofmatter can be represented this way: -3-

One phase can change into another phase, that is, solid can become liquid, andliquid can become gas. These changes are called phase changes. Study this diagram: Melting and freezing are reverse processes. Melting is the change of solid to liquid,while freezing is the change of liquid to solid. These changes are influenced by temperatureand pressure conditions.Process Temperature PressureMelting Needs higher temperatures Needs lower pressureFreezing Needs lower temperatures Needs higher pressure This table shows that in order to melt a solid, the temperature must go higher or thepressure must go lower. To see how this occurs, do this activity: What you will do Activity 1.1 The Candle Wax1. Light a candle and closely observe what happens to the candle wax.2. Answer these questions: a. Why did the wax melt? b. When did the melted wax turn solid again? -4-

Evaporation is the change from the liquid phase to the gas phase. This can be doneif the temperature is increased or the pressure is lowered. Condensation is the oppositeprocess of evaporation. It is the change from gas to liquid phase. The opposite conditionsare also needed. That is, the temperature must be lowered or the pressure must beincreased. Sublimation is the direct phase change from solid to gas, without passing through theliquid phase. This happens to substances like mothballs. Deposition is the oppositeprocess of sublimation. This is the direct change from gas to the solid phase, withoutundergoing condensation or freezing. What you will do Self-Test 1.1Directions: Fill in the blanks of this concept map. EvaporationMelting Key to answers on page 22.Lesson 2. When Does A Chemical Change Occur? Aside from phase changes, another group of changes is happening around us.These changes are called chemical changes. -5-

What you will do Activity 2.1 Identifying ChangesDo the following steps: Step 1: Cut a piece of paper into smaller pieces Step 2: Light a match Step 3: Mix vinegar and baking powder Step 4: Boil water Step 5: Boil water with egg whiteEach step shows a change. But which of them could be classified as a chemical change? A chemical change always results to the formation of a new substance. The surestway to know if a chemical change has occurred is to check if you observed one or more ofthese indicators of chemical change. 1. Change of color 2. Evolution of gas 3. Formation of precipitate Change of color. A change in color means that a new substance was formed afterthe chemical change. This new substance has different properties, including its color, fromthe original materials. The burning of the lighted match results in the change of color of the match. Beforelighting the match, the body is made of a pale colored wood and a red or black tip. Afterburning, the tip becomes black and charred. The pale color of the wood also becomesblack. It is no longer the original wood. Evolution of gas. Sometimes, you don’t see a color change after a chemicalchange. But you will find that gas is produced. This gas is the new substance. When youmix vinegar and baking powder, you will hear a fizzing sound and see gases bubble up.This gas is carbon dioxide. It is produced when the acetic acid of vinegar reacted with thesodium bicarbonate of the baking powder. Acetic acid + Sodium bicarbonate → carbon dioxide + other new substances -6-

Formation of precipitate. The precipitate is the solid material that appears in asolution, and this solid sinks or precipitates to the bottom of the container. This precipitateis the new substance formed from the chemical change. Which of the steps in the activityresulted in the formation of a precipitate? The role of temperature change. In the previous lesson, we learned that changingthe temperature would result to a phase change. This is what happened in step 4 of theactivity. But sometimes, changing the temperature results to a chemical change. This isshown in step 5. When none of these indicators can be observed, only a physical change hasoccurred. Phase changes are physical changes. Physical changes may show a change inshape, size, or volume. What you will do Self-Test 2.1Directions: Study each picture closely. Identify the chemical changes that you find.Picture 1 Picture 3 Key to answers on page 22. Picture 2 -7-

Lesson 3. Types of Chemical Changes In a chemical change or chemical reaction, the materials that are present before thereaction takes place are called the reactants. The materials that appear after the reactiontakes place are called the products. This means that a chemical change or chemicalreaction can be represented like this: There are four types of chemical reactions. These are: 1. Combination Reaction 2. Decomposition Reaction 3. Single Replacement 4. Double Displacement Combination Reaction. A combination reaction happens when two or morereactants form only one product. This is also known as the composition reaction or thesynthesis reaction. We can represent a combination reaction this way: A + Z → AZ For example, ethylene glycol is a substance used in making polyester fiber.Producing ethylene glycol is a combination reaction. Ethylene oxide + Water → Ethylene glycol Decomposition Reaction. A decomposition reaction happens when one reactantforms two or more products. This is also called a decay reaction. We can represent adecomposition reaction this way: AZ → A + Z -8-

For example, the anesthetic used by dentists is dinitrogen oxide. This is also calledlaughing gas. It is produced by the decomposition of ammonium nitrate. Ammonium nitrate → dinitrogen oxide + water Single Replacement Reaction. A single replacement reaction happens when areactant made of one element reacts with a compound, and replacing one of the elementsof the compound. We can represent a single replacement reaction this way: A + TZ → AZ + T For example, one side of a circuit board is made of copper. An electronics engineerwould like to remove some of the copper by submerging the circuit board in ferric chloride.What happens next is a single displacement reaction. The copper (Cu) atoms displaced theiron (Fe) atoms.3 Cu + 2 FeCl3 → 3 CuCl2 + 2 Fecopper ferric chloride copper chloride iron Double Displacement Reaction. A double displacement reaction happens whenthe elements in one of the reactants “exchange partners” with the other reactant. We canrepresent a double displacement reaction this way: AD + TZ → AZ + TD A special type of double displacement reaction is called neutralization. Inneutralization, an acid and a base react with and neutralize each other. The product is asalt and water. For example, hydrochloric acid reacts with sodium hydroxide to formsodium chloride (salt) and water. HCl + NaOH → NaCl + H2O Acid WaterHydrochloric Base Salt acid Sodium hydroxide Sodium chloride -9-

What you will do Self-Test 3.1Direction: Identify the type of reaction._______________ 1. The match head is made of tetraphosphorus trisulfide. Heating phosphorus and sulfur above 100OC makes this compound: P4 + 3S → P4S3_______________ 2. The components of water can be separated using electricity. 2H2O → 2H2 + O2_______________ 3. Carbon tetrachloride (CCl4), a compound used as a dry cleaning agent and a component in fire extinguishers, is made by this reaction: 2 S2Cl2 + C → CCl4 + 4S_______________ 4. Freon-12, CCl2F2, a substance used as refrigerant, is made by this reaction: CCl4 + 2HF → CCl2F2 + 2HCl_______________ 5. Ammonia, NH3, which is used in fertilizers, is formed by this reaction: N2 + 3H2 → 2NH3_______________ 6. Mn4Ga2S6 → 3MnS + Ga2S + S2_______________ 7. Al4C3 + 12H2O → 4Al(OH)3 + 3CH4_______________ 8. 3 Zn + 2H3PO4 → Zn3(PO4)2 + 3 H2_______________ 9. Al2(SO4)3 + 3Ca(NO3)2 → 3CaSO4 + 2Al(NO3)3_______________ 10. 2KClO3 → 2KCl + 3O2 Key to answers on page 23.Lesson 4. Chemical Changes Around Us Are you aware of the chemical changes that are happening around us? Let us studysome of them by reading the following:Chemical Changes in Our Body Chemical changes in our body are important. These changes keep us alive. Hereare some chemical changes in our body.Digestion We eat everyday, but what happens to the food that we eat? The carbohydrates, likesugars and starches, are broken down into blood sugar, called glucose, and this providesenergy for our body. - 10 -

C6H12O6 + O2 → 6CO2 + 6H2O + EnergyGlucose oxygen Carbon water dioxide If we eat too much carbohydrate some of the extra carbohydratesare stored in the liver as glycogen (animal starch) and the rest areconverted to fat. Too much fat can’t be safe. Do you watch the amountof carbohydrates you eat everyday?Exercise During exercise or any body activity, we contract our muscles. As this happens, theglycogen in our body is changed into pyruvic acid.If there is enough oxygen, this substance is changed into carbon dioxide and water. But if there is a lack of oxygen (maybe you did not breathe deeply?), the pyruvic acidchanges into lactic acid. When lactic acid builds up in your muscles, you will feel tired and weak. Somepeople also feel pain in their muscles. - 11 -

What you will do Activity 4.1 Which needs more oxygen? You will perform two activities to determine which of them require more oxygen inyour body. You will need a timer or a watch.Activity 1: Jog in place. Have a lively music in the background and keep pace with the rhythm of this music. How long can you jog before you feel that you’re already out of breath? Take at least 30 minutes rest before doing activity 2.Activity 2: Do jumping jacks. How long can you do this exercise before you feel out of breath? Which activity needs more oxygen?Chemical Changes At Home Chemical changes happen in our homes everyday because of the various activitiesthat we do at home. Let us identify some of them.Cleaning We must always clean our house or else it will look like a haven for pirates. And weuse different chemicals to clean the house. Before knowing more about these chemicals,let’s do this simple activity. What you will do Activity 4.2 Effect of Soap You may have done this everyday, but let’s take a much closer look at how soapworks. In a dirty plate, add a little water. And then pour two drops of dishwashing liquid orsoap into it. Write your observations here:___________________________________________________________________________________________________________________________________________________________________________________________________________________________ - 12 -

Basic soap is made of fat and lye. It is produced from the reaction of animal fat orvegetable oil with sodium hydroxide. Animal fat or Vegetable oil + NaOH → Soap Soap is a complex substance that has two main parts: the “polar head” and the“hydrocarbon tail” These two parts give soap the ability to clean. The Can you think ofhydrocarbon tail sticks into the oily stain or grease while the polar another way ofhead dissolves in water. The oily stain is broken down and cleaning thesebecomes easier to remove from your cloth, plate, or body. dishes? Dishwashing detergents like soap have the same parts,too. But these have other ingredients such as perfumes, color,and surfactants. Surfactants like LAS (linear alkylsulfonates)simply loosen food residue so that you can easily remove them.Cooking Cooking is also an activity that we do everyday. The chemical change that usuallyhappens is this: Uncooked food → Cooked food The change usually involves heat. Study this diagram: An egg undergoes a chemical change when cooked. The liquid egg coagulates orsolidifies when heat is applied. The meat of pork, chicken, and fish, also undergo chemical changes when heat isapplied. Vegetables also change when heat is applied. - 13 -

Sometimes, food undergoes a chemical change even if no heat is applied. Thishappens when food is being preserved. For example, salting raw fish makes bagoong. Meat is cured or preserved by adding salitre or sodium nitrite. Tocino, chorizo, andhotdogs are preserved this way.What you will doSelf-Test 4.1Directions: Identify whether the following is a physical or chemical change._______________ 1. Scrubbing the floor_______________ 2. Sweeping the backyard_______________ 3. Wiping the table_______________ 4. Making salad_______________ 5. Frying dried fish_______________ 6. Baking a cake_______________ 7. Bleaching cloth_______________ 8. Making syrup_______________ 9. Scraping food from the pan_______________ 10. Removing cobwebs Key to answers on page 23.Chemical Changes in the Environment The environment is one big chemical system where many complex and vital chemicalreactions happen. Here are some of them.Changes in Plants Plants undergo complex chemical changes. The stem grows Complexhigher, the roots go deeper, the flowers bloom, and the fruits ripen. The changes happenmost studied change in plants is the process of photosynthesis. Plantsmake their own food by photosynthesis. in plants The general chemical reaction for photosynthesis is: CO2 + H2O → C6H12O6 The carbon dioxide comes into the plant through the leaves and the roots absorbwater. With the presence of sunlight, these materials are changed into sugar. - 14 -

The Water Cycle The processes in water cycle are physicalchanges. Evaporation is a phase change in whichliquid water from lakes, rivers, and oceans is changedinto water vapor. Condensation of water vaporresults in the formation of clouds. And precipitationhappens when the clouds released water into theground as rain. In other countries, precipitation canbe in the form of snow.Changes in the Soil The Philippines is an agricultural country. Thismeans that many people depend on the soil for foodand livelihood. Many people are farmers. But as wecultivate the land, changes happen to the soil. The plants absorb minerals from the soil. As time goes by, less and less mineralsare left in the soil. To solve this problem, we use fertilizers. Fertilizers contain the threeprimary plant nutrients. These are nitrogen, phosphate, and potassium. Nitrogen can be added to the soil as ammonia. Ammonia can be produced using theHaber process. 3H2 + N2 → 2NH3 Phosphate fertilizers are produced by making a phosphate rock react with phosphoricacid. The product (calcium dihydrogen phosphate) is soluble in water and can be readilyabsorbed by plants. Ca3(PO4)2 + 4H3PO4 → 3Ca(H2PO4)2 Potassium in fertilizers is in a compound called potassium chloride, KCl. Thiscompound is mined. Most soils have potassium. Unfortunately, when plants take inpotassium, they leave the soil acidic.Corrosion Corrosion is another chemical change that happens all around us. One of the mostcommon forms of corrosion is the rusting of iron metals when it is exposed to air andmoisture. 4Fe + 3O2 + → 2Fe2O3 This final product is called iron (III) oxide or rust. To actually see how this happens,let’s do this activity. - 15 -

What you will doActivity 4.3 Rusting of Iron Nail You will need two tin covers of bottles and two nails. The nails should have no rustand must look exactly the same with each other. In one tin cover, place one nail. This isour set-up A. In another tin cover, place the other nail. But this time submerge half of thenail’s body in water. This is set-up B. Write your observations here.Day Set-up A Set-up B 1 2 3 4 5 What you will do Self-Test 4.2Direction: Read each change and write the possible results or products1. Water vapor encounters cold temperatures in the air: ___________________________2. Potassium is taken in by the roots of plants: __________________________________3. Plants perform photosynthesis: ____________________________________________4. Iron metal is exposed to air and water: ______________________________________5. Phosphate rock is treated with phosphoric acid: _______________________________ Key to answers on page 23.Chemical Reactions Used In Industries Many chemical changes have technological applications. These applicationsimprove our quality of life. At the same time, these chemical reactions are used profitably inseveral industries. We will present some of them here. - 16 -

Metal Industries Many things around us are made of metals, such asbuildings, bridges, houses, airplanes, ships, cars, andjeeps. Where did all these metals come from? Mostmetals are mined. But they are not mined in pure form.For example, copper can be taken from the copper sulfide(Cu2S) ore. And then this reaction is done: Cu2S + O2 → 2Cu + SO2 This is a reaction with oxygen (O2). A chemical reaction with oxygen is calledoxidation. The production of copper metal from its ore is an oxidation process. Iron is produced from its ore by using carbon monoxide in this chemical reaction: Fe2O3 + 3CO → 2Fe + 3CO2 This reaction is done in a blast furnace. The temperatures are very high and the ironproduced is called pig iron. Pig iron is also known as cast iron because it can be cast intomolds. But cast iron is brittle. To make it more useful, it is oxidized to produce steel. Aluminum is another important metal. The ore of aluminum is called bauxite, oraluminum oxide. Pure aluminum metal is extracted from this ore by passing electricitythrough it. electricity 2Al2O3 → 4Al + 3O2Plastics Plastics are also almost everywhere on our planet. They are used in innumerableways. Plastics are created through the process called polymerization. It is basically acombination reaction. For example, putting together many molecules of ethylene makes theplastic polyethylene. Ethylene is a gas while polyethylene is a solid which is used in plasticbags, bottles, toys, and electrical insulations Here are the other plastics, their monomers, and their uses. - 17 -