Science 3

What about ionization energy? electronegativity? electron affinity? OK, that’s a nice question! First, I would like you to know the meaning of these terms. Ionization energy is the energy required to remove the outer electron from an isolated atom. Electron affinity is the energy released when a neutral atom gains an extra electron to form a negatively- charged ion. Electronegativity is the electron attracting ability of an atom.Examine your periodic table. It will tell you that theionization energy for that element is quite small. Itwouldn't take much to send that one solitary electronsailing off into dizzying freedom--and that sort of thing,electrons leaving their home atoms, leads directly tochemical reactions. What does it tell you? The atomicradius is affected by the ionization energy,electronegativity and electron affinity. As you go acrossfrom left to right, ionization energy, electronegativity andelectron affinity increase, thus the atomic radiusdecreases. From top to bottom, ionization energy,electronegativity and electron affinity decreases, thusthe atomic radius increases. - 15 -

What you will doSelf-Test 2.11. Arrange the following elements according to decreasing atomic radius:a. As, P, Sb, N c. As, N, P, Sbb. Sb, As, P, N d. N, P, As, Sb2. Which of the following decreases as you go from left to right?a. atomic radius c. electron affinityb. ionization energy d. electronegativity3. Which of the following groups is a set of metals?a. Group VII A c. Group II Ab. Group IV A d. Transition elements4. Electron affinities of elements generally become smaller as we move from:a. top to bottom c. left to rightb. bottom to top d. diagonally5. The ability of an element to attract an electron from another atom is called:a. electronegativity c. ionization energyb. electron affinity d. metallic property Key to answers on page 27.Lesson 3. Electron Configuration and Order of Elements The electrons in the highest energy level of an atom are called valence electrons.This lesson will discuss how these electrons are distributed around their orbital. - 16 -

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What you will do Activity 3.1Read this comic strip and find out more about the arrangement of elements in the periodictable. After Mendeleev's time, scientists discovered what you already know: an atom consists of a positively charged nucleus, made of neutrons and protons, and electrons moving around it. This is shown by electron configuration. \"Electron configuration\"? I'm not sure if I understand what that means. How do I go about it? Does it have something to do with the \"s p d f\" ? - 18 -

Yes; Electron configuration shows how the electrons are arranged in the selected element. I'd be happy to explain how the electrons organize themselves. OK, examine the chart below.ssss ppppppss ppppppssd d d d d d d d d d p p p p p pssd d d d d d d d d d p p p p p pssd d d d d d d d d d p p p p p pss ffffffffffffff ffffffffffffff It says that groups IA s – sharp 2 electrons to filland IIA belong to the s p – principal 6 electrons to fill d – diffuse 10 electrons to fill block; groups IIIA to f – fundamental 14 electrons to fill VIIIA belong to the p block; the transition In determining the total number of metals to the d block and the lanthanides electrons in an energy level use the and actinides to the formula number of electrons = 2n2 f block. where n is the number of energy level; so for the first energy level there are 2 ; 2nd = 8 = (2+6); 3rd = 18 = (2 + 6 = 10); 4th = 32 = (2 + 6 + 10 + 14) But, how will I do it? Can you give me a pattern to make it easier and faster? - 19 -

Very easy! Just followthe arrows. The s, p, d and f are called sublevels; they are smaller \"subdivisions\" of energy within the primary levels. You refer to different energy levels using a number for the primary level plus a letter for the sublevel; for example, you might speak of an electron in a \"3p\" state or orbital. Each primary level has one more sublevel than the one below: the first primary level has only s orbitals, the second has s and p, the third s, p, and d, and so forth. - 20 -

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Below are samples of electron configuration of some elements: Elements Atomic Electron Configuration Period Group NumberHydrogen, H 1s1 1 IALithium, Li 1 1s22s1 2 IABerylium, Be 3 1s22s2 2 II ACarbon, C 4 1s22s22p2 2 IV ANitrogen, N 6 1s22s22p3 2 VAAluminum, Al 7 1s22s22p63s23p1 3 III ASulfur, S 13 1s22s22p63s23p4 3 VI APotassium, K 16 1s22s22p63s23p64s1 4 IABromine, Br 19 1s22s22p63s23p64s23d104p5 4 VII ADysprosium, Dy 35 1s22s22p63s23p64s23d104p65s24d105p66s24f10 6 II B 66Analysis of the Table: Take note of the coefficient of the last energy level. Notice also the exponent or thenumber on the superscript of the letter of the last energy level. The coefficient represents the series or the period of the element and thesuperscript or the exponent represents the number of electrons in the outermost energylevel or simply the valence electrons. It is also the Family or the Group Number of theelement. What you will do Self-Test 3.1Fill up the columns: 1. Write the electron configuration. 2. Identify the period and group number without looking at your periodic table. - 22 -

Elements Atomic Electron Configuration Period Group NumberMagnesiumChromium 12Silicon 24Galium 14Krypton 31Rubidium 36Silver 37Antimony 47Iodine 51Barium 53 56 Key to answers on page 28.Lesson 4. Importance of Some Elements in the Human Body This lesson tackles the different uses of elements in the periodic table. Some ofthese elements are essential to our lives, in industry and in modern technologies.Group I A – The Alkali Metals Group 1A elements are soft silvery metals. They are highly reactive with water and melt at low temperature. Because of their reactivity, they are never found free in nature. Compounds of these elements like sodium chloride or table salt is a fundamental part of the diet; potassium compounds are important nutrients for plants. Potassium nitrate, KNO3, commonly known as salitre, is used in making tocino.Group II A – The Alkaline Earth Metals This group consists of all metals that occur naturally in compound form. They are obtained from mineral ores and form alkaline solutions. These are less reactive than alkali metals. Magnesium (Mg) and calcium (Ca) are the most abundant elements in the earth’s crust. Calcium is one of the important elements in teeth and bones. Radium, the heaviest alkaline metal, is used for cancer treatment.Group III A – The Aluminum Group The elements in this group are fairly reactive. The group is composed of four metals and one metalloid, which is boron. Aluminum is a metal abundantly found in the earth’s crust. It is used as a raw material for kitchenware due to its low density - 23 -

property. Others, such as gallium is used as semiconducting material in the form of gallium arsenide.Group IV A – The Carbon Group This group is composed of elements having varied properties because their metallic property increases from top to bottom meaning the top line which is carbon, is a non- metal, silicon and germanium are metalloids while tin and lead are metals. Carbon is the major constituent of most chemical compounds. Tin alloys are used in making weapons, cutting utensils and for canning of foods. Lead is an additive for paint and for plumbing purposes.Group V A – The Nitrogen Group Like the elements in group IV A, this group also consists of metals, a nonmetal and metalloids. Nitrogen gas makes up three-fourths of the earth’s atmosphere. This gas is useful in preparing ammonia and fertilizers.Group VI A – The Oxygen Group The elements in this group like the sulfur and selenium are essential components in the human diet.Group VII A – The Halogens Fluorine is a major component of the chlorofluorocarbons (CFCs) that are used as aerosols and refrigerants. Chlorine is used as bleaching agent. Bromine, known to us as the only liquid metal, is used in the manufacture of photographic films and dyes, while an isotope of iodine, iodine 131, is used in thyroid gland treatment. Iodine is also used in the preparation of iodized salt that refreshes and prevents memory gap.Group VIII A – The Noble Gases The element helium is used for balloon inflating since it is very light. Argon and neon are used as advertising lights.The transition elements These elements are lanthanides compounds that are used as “green TV” or colored picture tube. Uranium isotopes are used as fuel for nuclear reactors. Americium is used as “smoke detector’. - 24 -

What you will doSelf-Test 4.1Match Column A with Column B. ELEMENT USE(S)1. americium a. used as constituent of “green TV”2. iodine 131 b. heaviest metal used for cancer treatment3. potassium c. ¾ of the earth’s atmosphere compound d. used in aerosols4. calcium compound e. raw material for kitchen wares5. nitrogen f. an element from group IIA found in the earth’s6. magnesium crust7. neon g. advertising lights8. lanthanide metals h. used as preservative9. aluminum i. used as smoke detector10. radium j. used for thyroid gland treatment Key to answers on page 28. Let’s SummarizeA. Development of the Periodic Table 1. Johann Wolfgang Dobereiner classified elements in sets of three. He called it the “law of triads” 2. John Alexander Reina Newlands arranged the elements according to increasing atomic mass and suggested that every eighth element has similar properties. He called his law the “law of octaves”. 3. Dmitri Inovich Mendeleev devised the first periodic table, which he used to predict three new elements. He proposed the ”periodic law” which states that when elements are arranged in order of increasing atomic number, their properties show periodic pattern.B. The Periodic Table and the Elements 1. The periodic table is composed of 7 rows or periods and 18 major groups or columns. Elements in a group have similar properties particularly those elements in four of the groups: Group IA – The alkali metals; Group II A - the alkaline earth metals; Group VII A – the halogens and Group VIII A – the noble gases. - 25 -

2. The elements are given symbols devised by John Jacob Berzelius. An element is named after its discoverer, place of discovery, first letter of the name of the element, first and the second letter for those having the same first letter and some are after their Latin names. The elements are grouped into Group A and B Group by the INTERNATIONAL UNION OF PURE AND APPLIED CHEMISTRY (IUPAC). 3. Elements in the periodic table are also grouped according to metals, non-metals and metalloids. Metals are lustrous, malleable and ductile. They are good conductors of heat. Metals are found on the left side of the periodic table. Nonmetals have a diverse set of properties. They are found on the upper right side of the periodic table. Metalloids or semimetals possess the properties of both the metals and the non-metals.C. Periodic Trends 1. A periodic trend is a property that changes as you move across a period or down a group of the periodic table. 1. Atomic radius increases as you move down a group and decreases as you move across. 2. Ionization energy is the energy needed to remove an electron to form a positive ion. - 26 -

3. Electron affinity is the energy change that occurs when an atom gains an electron to form a negative ion.4. An element’s electronegativity reflects its attraction for electrons in a chemical bond.D. Electron Configuration and Order Among Elements1. The distribution of electrons among the orbitals of an atom is its electronconfiguration.2. s – sharp 2 electrons to fillp – principal 6 electrons to filld – diffuse 10 electrons to fillf – fundamental 14 electrons to fillTotal number of electrons in an energy level can be found by the formula number of electrons = 2n2Where n is the number of energy level; 1st energy level there are 2 ; 2nd = 8 = (2+6) 3rd = 18 = (2 + 6 = 10); 4th = 32 = (2 + 6 + 10 + 14)3. The s, p, d, and f are called sublevels; they are smaller \"subdivisions\" of energy within the primary levels. You refer to different energy levels using a number for the primary level plus a letter for the sublevel; for example, you might speak of an electron in a \"3p\" state or orbital. Each primary level has one more sublevel than the one below: the first primary level has only s orbitals, the second has s and p, the third s, p, and d, and so forth. - 27 -

PosttestI. Multiple Choice. Choose the letter of the best answer. Write the chosen letter on aseparate sheet of paper.1. The lowest sublevel in each principal energy level is thea. s b. p c. d d. f2. Which among the elements is an alkali metal?a. boron c. sodiumb. magnesium d. oxygen3. Elements in the 4f series are called: c. actinides a. alkali metals d. lanthanides b. alkaline earth metals4. What is the most abundant element in the universe?a. oxygen c. siliconb. carbon d. aluminum5. Which transition metal is the best conductor of electricity?a. copper c. chromiumb. silver d. iron6. Which of these metals are soft enough to be cut by a knife?a. alkaline metals c. transition metalsb. alkali metal d. all of these7. Among the groups in the periodic table, which set of elements are the least reactive?a. Lanthanides c. Halogensb. actinides d. Inert gases8. The scientist who grouped the elements into sets of three isa. Mendeleev c. Dobereinerb. Newlands d. Moseley9. As you move from left to right of the periodic table, the elements - 28 -

a. increase in atomic radius c. decrease in electron affinityb. increase ionization energy d. have no periodic trends10. The energy change when an electron is added is called:a. ionization energy c. electron affinityb. electronegativity d. reactivity - 29 -

11. How many elements are in the second period of the periodic table? a. 2 b. 4 c. 6 d. 812. How many electrons do the elements belonging to Group IIIA have in their outermost shell? a. 1 b. 2 c. 3 d. 413. Which orbital is being filled in the actinides series of elements?a. 4f b. 4d c. 5f d. 5d14. Who stated the “law of Octaves’? c. John Alexander Newlands a. Johann Wolfgang Dobereneir d. John Dalton b. Dmitri Inovich Mendeleev15. In electron configuration, what does the number before the sub-energy level represent?a. Period c. total number of electronsb. Group d. number of outermost electronsII. Matching Type: Match Column A with Column B COLUMN A COLUMN B1. halogens group a. electron configuration2. noble gases b. B Group3. alkali metals c. Group I – A4. carbon group d. Group II – A5. alkaline earth metals e. Group III – A6. transition metals f. Group IV A7. aluminum group g. Group V A8. oxygen group h. Group VI A9. Nitrogen group i. Group VII A10. electron distribution j. Group VIII AIII. Complete the Table below. (Don’t look at your periodic table) Elements Atomic Electron Configuration Period Group Number1. Sodium, Na2. Titanium, Ti 113. Phosphorus,P 224. Fluorine, F 155. Chlorine, Cl 9 17 Key to answers on page 28. - 30 -

Key to AnswersPretestI. Multiple Choice 6. a 11. c 1. b 7. a 12. a 2. a 8. b 13. c 3. b 9. c 14. d 4. c 10. c 15. d 5. cII. Fill in the Blanks 1. John Newlands 2. electron configuration 3. metalloids 4. inert gases or noble elements 5. series or period numberLesson 1Self-Test 1.11. Johann Wolfgang Dobereiner2. Triads3. Alexander Reina Newlands4. Octaves5. Dmitri MendeleevLesson 2Self-Test 2.11. b2. a3. c4. a5. a - 31 -

Lesson 3Self-Test 3.1 Elements Atomic Electron Configuration Period Group NumberMagnesium 1s22s22p63s2 3 II AChromium 12 1s22s22p63s23p64s23d4 4 VI BSilicon 24 1s22s22p63s23p2 3 IV AGalium 14 1s22s22p63s23p64s23d104p1 4 VAKrypton 31 1s22s22p63s23p64s23d104p6 4 VIII ARubidium 36 1s22s22p63s23p64s23d104p65s1 1 IASilver 37 1s22s22p63s23p64s23d104p65s14d10 5 IBAntimony 47 1s22s22p63s23p64s23d104p65s24d105p3 5 VAIodine 51 1s22s22p63s23p64s23d104p65s14d105p1 5 VII ABarium 53 1s22s22p63s23p64s23d104p65s14d105p66s2 6 II A 56Lesson 4Self-Test 4.1 ELEMENT USE(S)1. americium i. used as smoke detector2. iodine 131 j. used for thyroid gland treatment3. potassium compound h. used as preservative4. calcium compound d. used in gypsum making5. nitrogen c. ¾ of the earth’s atmosphere6. magnesium f. an element from group IIA found in the earth’s7. neon crust8. lanthanide metals g. advertising lights9. aluminum a. used as constituent of “green TV”10. radium e. raw material for kitchen wares b. heaviest metal used for cancer treatmentPosttest 6. a 11. d 7. d 12. cI. Multiple Choice 8. c 13. c 9. b 14. c 1. a 10. b 15. a 2. b 3. d 4. d 5. b - 32 -

II. Matching Type COLUMN B i. Group VII A COLUMN A j. Group VIII A 1. halogens group c. Group I – A 2. noble gases f. Group IV A 3. alkali metals d. Group II – A 4. carbon group b. B Group 5. alkaline earth metals e. Group III – A 6. transition metals h. Group VI A 7. aluminum group g. Group V A 8. oxygen group a. electron configuration 9. nitrogen group 10. electron distributionIII. Complete the Table below: Elements Atomic Electron Configuration Period Group Number1. Sodium, Na 1s22s22p63s1 3 IA2. Titanium, Ti 11 1s22s22p63s23p64s23d2 4 IV B3. Phosphorus,P 22 1s22s22p63s23p2 3 VA4. Fluorine, F 15 1s22s22p5 2 VII A5. Chlorine, Cl 9 1s22s22p63s23p5 3 VII A 17ReferencesHagad, R.H. (2003). Chemistry. Quezon City, Philippines: ALCO Printers.Lemay, E.H & Beall, H. (2002). Chemistry in the changing world. USA: Prentice Hall.Mendoza, E. & Religioso, T. (2001). Chemistry. Quezon City, Philippines: SIBS Publishing.Nueva España, R.C. & Apostol, J. (2004). Chemistry. Quezon City, Philippines: Abiva Publishing.Oxtoby, D.W. & Freeman, W.A. (1998). Chemistry: The science of change. CA: Saunders College Publishing. - 33 -

Module 12 Chemical Nomenclature What this module is about What’s in a name? It is not known when humans first began using names though the practice is certainlyvery old, probably extending far into prehistory. Although all cultures use names, namingcustoms vary greatly from people to people. Names serve several purposes. Most importantly, they help us distinguish peoplefrom one another. Imagine how difficult it would be to refer to people if we did not usenames. Instead of saying Bob one would have to say something like the short red-headedman who lives down the street. Some names carry information about our roots, such asfamily or clan names. They are generally inherited. Names can serve other purposes aswell, such as the Chinese generation name which identifies the generation of the bearer, orthe names used by some African cultures which describe the order in which siblings wereborn. Like human beings, compounds also have names. Chemical nomenclature is theterm given to the naming of compounds. It is used to identify a chemical species by meansof written or spoken words. It is a useful means for communication among chemists. Thename of the compound contains within itself an implied relationship to the structure of thecompound. This helps the reader or listener deduce the structure (and thus the identity) ofthe compound. But this purpose requires a system of principles and rules, the application ofwhich gives rise to a systematic nomenclature. This module on chemical nomenclature contains these lessons:  Lesson 1 – Chemical Symbol  Lesson 2 – Chemical Formula  Lesson 3 – Empirical Formula and Molecular Formula What you are expected to learn After going through this module, you are expected to:

1. Trace the historical background of chemical symbols.2. Identify and memorize the symbols of common elements.3. Recall and apply the rules in writing and naming different compounds.4. Differentiate between empirical and molecular formulas.5. Determine the empirical and molecular formulas of compounds. How to learn from this moduleHere 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 lesson in this module3. Check your answers against the key to answers 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 learned.6. Take the 10-item multiple–choice test at the end of the module. Good luck and have fun!What to do before (Pretest)I. Multiple Choice. Choose the letter of the best answer. Write the chosen letter on aseparate sheet of paper.1. Which of the following is a binary ionic compound?a. CO2 c. CaCl2b. CCl4 d. CaCO32. Which compound is commonly called laughing gas?a. N2O c. N2O3b. NO2 d. NO3-1 -2-

3. Which of the following substances is used to neutralize acid in the stomach that causeshyperacidity?a. MgCO3 c. Mg(OH)2b. MgCl2 d. MgO4. What is the common suffix used in naming binary inorganic compounds?a. ∼ ate c. ∼ icb. ∼ ite d. ∼ ide5. What polyatomic ion is commonly found in basic compounds?a. Acetate c. Cyanideb. Bicarbonate d. Hydroxide6. Which of the following does NOT belong to the group?a. Al2O3 c. AlCl3b. AlPO4 d. AlP7. What is the best way of naming C2O42-? c. carbon oxide a. Oxalate d. carbon dioxide b. dicarbon tetroxide8. Which of the following is also known as hydrosulfuric acid?a. H2S c. H2SO4b. H2SO3 d. H2S2O3For numbers 9 to 10, refer to the following choices:a. CaSO4 c. MgSO4b. CuSO4 d. BaSO49. What compound is also known as gypsum?10. What compound is also known as Epsom salt? -3-

II. Matching Type. Match the term/discoverer in column B with its definition/discovery incolumn A. Write the letter of your choice on a separate sheet. Column A Column B_____ 1. shorthand representation of elements a. America_____ 2. simplest formula b. Argentina_____ 3. the number written after the symbol of the c. Covalent d. Cuprum element e. Empirical_____ 4. English name for natrium f. Ferrum_____ 5. shorthand representation of compounds g. Formula_____ 6. the inventor of the element oxygen h. H2O_____ 7. the country where the element silver i. H2O2 j. Ionic originated from k. Lavoisier_____ 8. the Latin name of the element iron l. Molecular_____ 9. a type of compound composed of metallic m. Priestly n. Sodium and nonmetallic elements o. Subscript_____10. the molecular formula of the compound p. Symbols aqua oxigenada Key to answers on page 17.Lesson 1. Chemical Symbol There are 114 known elements at present. Ninety-two of these are found in natureand the others are produced in the laboratory. Among the 114 elements, 11 are known tobe gases. Some of these are oxygen, hydrogen, nitrogen, chlorine, and helium. Elementslike neon, argon, krypton,xenon,radon, and fluorine are very rare and are not found in largequantities in nature. All the rest are solids. Now, each element has been given a name and a symbol. It was not always like this.Before the year 1814, the chemical symbols were expressed this way:Element Symbol Iron ♂Copper ♀ Gold Ο -4-

Then Jon Jacob Berzelius (1779-1848), a Swedish chemist, started to use chemicalsymbols. He used the initial letter of the element’s Latin or common name in its capitalizedform as its chemical symbols as follows: C = carbon O = oxygen I = iodine This practice is still followed today. If the two elements start with the same letter, twoletters are used as in the following: Ca = calcium Co = cobalt The symbols of other elements are related to their Latin names like the following:Elements Latin name Symbol Elements Latin Symbol nameAntimony Stibium Sb Lead Plumbum PbCopper Cuprum Cu Potassium Kalium KGold Aurum Au Silver Argentum AgIron Ferrum Fe Sodium Natrium NaMercury Hydrargyrum Hg Tin Stannum Sn What do you think is the symbol for each of the following elements? a. hydrogen b. helium c. boron d. barium The table below could help you memorize the symbols of some common elements,their discovery and their Latin name, if there is. Name Date Discoverer Latin Name SymbolCarbon antiquity Unknown None CGold antiquity Unknown Aurum AuSilver antiquity Unknown Argentum AgCopper antiquity Unknown Cuprum CuSulfur antiquity Unknown None STin antiquity Unknown Stannum SnLead antiquity Unknown Plumbum PbMercury antiquity Unknown Hydrargyrum HgIron antiquity Unknown Ferrum Fe -5-

Name Date Discoverer Latin Name SymbolArsenic 1250 None As Albertus Magnus is Stibium Sb believed to have been None Bi the first to isolate the None Zn element. None PAntimony 1450 First described None Co None Pt scientifically by None Ni Tholden None Mg None OBismuth 15th May have been None N century? None Cl described in writings None Mn None H attributed to Basil Valentinus, definitively identified by Claude Geoffroy Junine in 1753Zinc 1526 Identified as a uniquePhosphorus 1669 metal by Paracelsus Hening Brand, later described by Robert BoyleCobalt 1732 Georg BrandtPlatinum ca. 1741 Discovered independently by Antonio de Ulloa (published 1748) and Charles Wood.Nickel 1751 Axel Fredrik CronstedtMagnesium 1755 Joseph BlackOxygen 1771Nitrogen 1772 Joseph PriestleyChlorine 1774Manganese 1774 Daniel Rutherford Carl Wilhelm Scheele Johan Gottlieb Gahn Isolated andHydrogen 1776 described by Henry Cavendish, named by Antoine Lavoisier -6-

What you will doActivity 1.1Welcome to the Elemental - Element Crossword Puzzle! Given at the right are the symbols of different elements. Complete the crosswordpuzzle by figuring out the elements that they represent.Good luck and have fun! 1 4 Easy2 8 Symbols Across 3 2. He 5 67 3. N 6. C 9 9. I 10 10. U Down 1. Li 4. Ne 5. Al 7. Ar 8. O Key to answers on page 17.What you will doSelf-Test 1.1Multiple Choice. Choose the letter that corresponds to the best answer. Write your choiceon a separate paper.1. What is the correct symbol for cuprum? c. Cp a. C d. Cr b. Cu -7-

2. Which of the following does NOT belong to the group?a. Argentum c. Calciumb. Aurum d. Kalium3. Which of the following elements is the youngest?a. argon c. heliumb. carbon d. hydrogen4. What is the English name of stibium? c. lead a. antimony d. tin b. arsenic5. Which of the following does NOT belong to the group?c. carbon c. nitrogend. hydrogen d. oxygen Key to answers on page 18. 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. Chemical FormulaChemical Formulas Chemical formulas such as MgSO4 can be divided into empirical formula,molecular formula, and structural formula. The chemical symbols of elements in thechemical formula represent the elements present in the compound. The subscript numbersrepresent mole proportions of the preceding elements. If no number is written, it means thesubscript is 1.The Writing of Formulas Compounds formula can be written in several forms. In this area we will discuss howto write the formula of a simple binary ionic compound (compound composed of metaland a nonmetal) whose name is known. The metal acts the cation (positively-charged ion)while the nonmetal forms the anion (negatively-charged ion). The first part of the name ofan inorganic compound is the first part of the formula. -8-

Formula Writing of Binary Ionic compoundsCharge – Crossing TechniqueRules to follow:  The total positive charges must equal the total negative charges.  Do not change the charges given to you.  Adjust the subscripts to equalize the charges.Suppose you want to write the formula for the common table salt, sodium chloride.Write down the Na+ and Cl- right next to each other, as in this image: Na1+ Cl1-Move the positive charge (dropping the sign) to the subscript position of theanion:Move the negative charge (dropping the sign) to the subscript position of thecation:The result is:Since subscripts of one are not written but are understood to be present, thefinal answer is:Write the formula for aluminum oxide.Write down the Al3+ and O2- right next to each other:Move the positive charge (dropping the sign) to the subscript position of theanion:Move the negative charge (dropping the sign) to the subscript position of thecation:This results to: What you will do Activity 2.1Write the correct formula of the following compounds: -9-

1. hydrogen chloride (you must know that this is the common muriatic acid for cleaning purposes)2. calcium fluoride (do you still remember the anti tartar ingredient of your toothpaste?)3. sodium oxide (the substance behind the cleansing principle of your laundry detergent) Key to answers on page 18.The Naming of Compounds: NomenclatureIdentifying a Compound as Ionic or Molecular In naming compounds, you have to decide first whether you are looking at an ioniccompound or a molecular compound. We know that metals combined with nonmetals willproduce compounds that are ionic. Nonmetals combined with nonmetals will producecompounds that are molecular. For example: MgCl2 would be ionic because it has the chloride ion which is anonmetal combined with magnesium which is a metal. Metals combined with nonmetalsproduce ionic compounds.Nomenclature of Binary Ionic Compounds A binary compound is made up of two different elements. There can be one of eachelement such as in NaCl or KF. There can also be several of each element such as Na2Oor AlBr3.Please remember that all elements involved in this lesson have ONLY ONE charge.Points to remember about naming a compound from its formula1. The order for names in a binary compound is first the cation, then the anion.2. Use the name of cation directly from the periodic table.3. The name of the anion will be made from the root of the element's name plus the suffix \"-ide.\"Example: Write the name of this formula: H2SSteps Look at the first element and name it Results 1 Look at second element. Use the root Hydrogen 2 of its full name (which is sulf-) plus the ending \"-ide.\" sulfide - 10 -

These two steps give the full name of H2S. Notice that the presence of the subscriptis ignored.Nomenclature of Acids and Bases For the purposes of naming acids and bases, we will classify these chemicals intothree categories: binary acids, ternary acids (sometimes called oxy-acids), and bases.Binary Acids Binary acids contain hydrogen and one other nonmetallic element. Their namesfollow the pattern of \"hydroelementic acid\" where element is replaced by the root of thename of the element. These acids contain no oxygen. Here are some examples. HF hydrofluoric acid H2S hydrosulfuric acid HBr hydrobromic acid Note that the names of binary acids do not indicate how many hydrogen atoms are inthe formula. That is determined by the valence of the other element.Bases Bases are simply named as ionic compounds containing the hydroxide ion. Here aresome examples. NaOH sodium hydroxide Ca(OH)2 calcium hydroxide Fe(OH)3 iron(III) hydroxide NH4OH ferric hydroxide ammonium hydroxide What you will do Activity 2.2Try answering the following exercises:Matching type. In Part A, match the name of the compound in column A with its formula incolumn B. In Part B, match the formula of the compound in column A with its name incolumn B. - 11 -

Column A Column BA. Formula Writing a. AlBr3 1. Sodium Bromide b. AlCl 2. Barium Phosphide c. Ba3P2 3. Calcium Oxide d. CaO 4. Lithium Sulfide e. L2S 5. Aluminum bromide f. NaBrB. Naming a. Barium sulfide 1. MgI2 b. Hydrogen fluoride 2. K2O c. Hydrogen chloride 3. LiCl d. Magnesium iodide 4. BaS e. Lithium chloride 5. HF f. Potassium oxide Key to answers on page 18.Before going to the next lesson, try answering the following:What you will doSelf-Test 2.1Multiple Choice. Choose the letter that corresponds to the best answer. Write your choiceon a separate paper.1. Which of the following formulas is an acid?a. Na2CO3 c. H2Ob. NaOH d. HCl2. Which of the following is the correct formula for magnesium chloride?a. MgCl2 c. MgCO3b. Mg2CO3 d. Mg(CO3)23. Which of the following represents the correct name for BaO?a. Barium oxide c. Beryllium oxideb. Boron oxide d. none of the above4. Which does NOT belong to the group? c. HF a. HclO d. H3N b. HCl - 12 -

5. What is the correct formula formed if Al+3 is combined with S-2?a. Al3S2 c. Al2S3b. Al2S3 d. None of the above Key to answers on page 18. 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. Empirical and Molecular Formula Empirical (Simplest) formula is a formula whose subscripts represent the simplestwhole number ratio of atoms in a molecule or the simplest whole number ratio of moles ofeach element in a mole of the compound. The simplest formula is usually determined byconsidering experimental data, hence the name \"empirical\" which means based onexperimentation. It speaks of relative numbers. For example, CH2 says that there will betwice as many hydrogens as there are carbons in the compound that has this simplestformula. It does not give the exact numbers of hydrogens and carbons in the compound. On the other hand, molecular formula gives the exact number of atoms of eachelement per molecule of the compound or the absolute number of moles of each elementper mole of the compound. A molecular formula may be reducible to a simple formula if allits subscripts are divisible by a common denominator. Some compounds have the same empirical and molecular formula. For example,carbon dioxide has CO2 as its empirical and molecular formula. The empirical andmolecular formula for sulfur dioxide is also the same: SO2. There are many situations where two or more compounds have the same simplestformula but different molecular formulas. For example, benzene and acetylene have thesame simplest formula, CH. However, benzene's molecular formula is C6H6 andacetylene's molecular formulas is C2H2. The table below shows examples of the empiricaland molecular formula of certain compounds. Table 1. Comparing Empirical and Molecular Formulas Compound Molecular Formula Empirical FormulaWater H2O H2OHydrogen Peroxide H2O2 HOSodium phosphide Na3P Na3PMagnesium sulfide Mg2S2 MgS - 13 -

To determine the molecular formula of the compound, just follow these steps: 1. Find the mass of the empirical unit. 2. Figure out how many empirical units are in a molecular unit. 3. Write the molecular formula.Example: A compound with an empirical formula of CH has a molar mass of 78. What is itsmolecular formula?Answer: Step #1. C : 12 x 1 = 12 H : 1 x 1 = 1_ 13 Step #2. 78/13 = 6 Step #3. (CH)6 = C6H6 On the other hand, if the empirical formula is asked, simply divide the subscripts ofthe molecular formula with the greatest common factor. The resulting SIMPLEST WHOLENUMBER represents the subscript in the empirical formula.Example: What is the empirical formula of the compound Na2C2O4?Answer: Just divide the subscripts of the molecular formula by the greatest common factor.The resulting empirical formula is NaCO2. What you will do Activity 3.1Try to fill in the table with the empirical or molecular formula of the compound.Molar mass Molecular Empirical mass Empirical 34 formula 342 formula C12H22O11 (table sugar) HO CH2O C6H12O6 Key to answers on page 18. - 14 -

What you will doSelf-Test 3.1Direction: Write A if the given formula of the compound is empirical. Write B if it is amolecular formula. Write your choice on a separate paper.1. BaSO42. KMnO43. Sn2O44. Al3P35. PbS2 Key to answers on page 18. If you scored 3 or more out of 5 – CONGRATULATIONS!We have come to the end of the module. If you scored below 3, you need to go back andread the lesson again! Let's Summarize1. The symbols of the elements that we are using at present evolved from the ideas presented by Lavoisier, Dalton and Berzelius. They are patterned after Berzelius’ concept. The following are the rules that Berzelius employed in his system of writing chemical symbols: a. In metalloids, use the initial letter only, even when this letter is common to the metalloid and some metal. b. In metals, distinguish those that have the same initials with another metal, or a metalloid, by writing the first two letters of the word. c. If the first two letters are common to two metals, in that case, add to the initial letter the first consonant which they do not have in common: for example, S = sulphur, Si = silicon, St = stibium (antimony), Sn = stannum (tin), C = carbon, Co = cobaltum (cobalt), Cu = cuprum (copper), O = oxygen, Os = osmium.2. A chemical formula (also called molecular formula) is a concise way of expressing information about the atoms that constitute a particular chemical compound. It identifies each type of element by its chemical symbol and identifies the number of atoms of such element to be found in each discrete molecule of that compound. The number of atoms (if greater than one) is indicated as a subscript. For nonmolecular substances the subscripts indicate the ratio of elements in the empirical formula. - 15 -

3. The formula could be empirical, molecular or structural.4. There are different systems by which a compound’s formula could be written or named. The choice of system is based on whether the compound is binary, ionic or covalent, ternary, or acids or bases.5. The compound’s empirical and molecular formulas can be determined using these steps: a. Empirical formula determination  Divide each subscript of the molecular formula by the greatest common factor.  The resulting SIMPLEST WHOLE NUMBER represents the subscript in the empirical formula. b. Molecular formula determination  Find the mass of the empirical unit.  Figure out how many empirical units are in a molecular unit.  Write the molecular formula.PosttestMultiple Choice. Choose the letter that corresponds to the best answer. Write your choiceon a separate paper.1. What is a chemical compound? a. The combination of elements. b. The combination of two or more different elements. c. The combination of two or more similar elements.2. How many atoms of oxygen are in the formula H2SO4?a. 2 b. 4 c. 83. How many atoms of oxygen are in the formula C3H5(NO3)3?b. 3 b. 6 c. 94. What is the correct formula of calcium sulfide?a. CaS4 b. Ca2S2 c. CaS5. The algebraic sum of all the oxidation numbers of elements in a compound isa. 2 b. 1 c. 06. Alkali metals have an oxidation number ofa. +1 b. +2 c. –1 - 16 -

7. Caffeine, a primary stimulant in coffee and tea, has a molecular formula of C8H10N4O2.Which of the following represents its empirical formula?a. C2H5N2O b. C4H5N2O c. C8H10N4O28. What is the empirical formula of a compound that contains K2C2O4?a. K2CO3 b. KCO2 c. K(CO3)29. What is the molecular formula of the compound with an empirical formula of CH2, andmolar mass = 84 g/mol?a. C3H6 b. C6H12 c. C9H1810. What is the molecular formulas of Ibuprofen if its empirical formula is (C7H9O) and itsmass is 109 with a molar mass of 218 g/mol?a. C13H18O2 b. C12H18O2 c. C14H18O2 Key to answers on page 19.If you scored 7 or more out of 10 – Congratulations! You may now proceed. If you scoredbelow 7, you need to go back and read the module again!Key to AnswersPretest 6. a II. 6. m 7. a 1. p 7. b I. 8. a 2. e 8. f 1. c 9. a 3. o 9. j 2. a 10. c 4. n 10. i 3. c 5. g 4. d 5. d Down 1. lithiumLesson 1 4. neon 5. aluminumActivity 1.1 7. argon 8. oxygen Across 2. helium 3. nitrogen 6. carbon 9. iodine 10. uranium - 17 -

Self-Test 1.1 B Self-Test 2.1 1. d 1. c 2. f 1. d 2. c 3. e 2. a 3. d 4. a 3. a 4. a 5. b 4. a 5. a 5. aLesson 2 Molecular Empirical mass Empirical formula 342 formulaActivity 2.1 C12H22O11 C12H22O11 (table sugar) 17 1. HCl 30 HO 2. CaF2 H2O2 CH2O 3. Na2O C6H12O6Activity 2.2 A 1. f 2. c 3. d 4. e 5. aLesson 3Activity 3.1 Molar mass 342 34 180Self-Test 3.1 1. a 2. a 3. b 4. b 5. a - 18 -

Posttest 6. a 7. b 1. b 8. b 2. b 9. b 3. c 10. c 4. c 5. cReferencesBooks:Chang, R. (2005). Chemistry. Arizona: McGrawHill.Redmore, F. (1998). Fundamentals of chemistry. San Diego, CA.: Prentice-Hall.Electronic Sources:R. H. Logan. Types of chemical formula. Retrieved March 15, 2005 from http://members.aol.com/profchm/formulas.html.Ron Kurtus. (revised 10 November 2004). Chemical formula. Retrieved March 30, 2005 from http://www.school-for-champions.com/science/chemformulas.htm.S.E. Van Bramer. Chemical nomenclature problem set. Retrieved April 2, 2005 from http://science.widener.edu/svb/pset/nomen_a.html.Van der Krogt, P. Elementymology and elements multidict. Retrieved February 23, 2005, from http://www.vanderkrogt.net/elements/chemical_symbols.html.Retrieved February 23, 2005 from http://www.science.uwaterloo.ca/~cchieh/cact/c120/ formula.html.Retrieved February 23, 2005 from http://chemsite.lsrhs.net/d_Equations_and_Formulas/ naming_strategy.html.Retrieved March 15, 2005 from http://www2.potsdam.edu/walkerma/EmpForm.pdf. - 19 -

Module 13 Chemical Reactions What this module is about Chemical reactions take place in our surroundings as fast as we can take air forbreathing. A very pleasant reaction takes place in our homes while preparing grilled fish orpork for the evening meal. The glowing charcoal that cooks the fish or pork consists almostentirely of the element carbon. It burns slowly with oxygen of the evening air. When carbonand oxygen combine together, what compound is produced? While taking your shower, have you ever wondered how the soap is made? Haveyou ever thought that regardless of color, shape and brand its main function is to take off dirtfrom the body? As the cars and buses move, have you thought about how these machines work?Did you know that chemical reactions take place inside the car batteries? These are just examples of chemical changes that we find in our environment.These changes have been found to comply with several basic laws of nature. This moduleintroduces you to these laws. In addition to that, we will learn how to write sample chemical reactions and translatethem into chemical equations. This module will lead you to the beauty of the chemicallanguage to the extent that you will be able to write it, read it and interpret its meaning.  Lesson 1 – Law of Conservation of Mass  Lesson 2 – Law of Definite Proportions  Lesson 3 – Law of Multiple Proportions  Lesson 4 – Writing Chemical Reactions and Balancing Chemical Equations What you are expected to learn After going through this module, you should be able to: 1. identify reactants and products. 2. evaluate chemical equations that conform with the law of conservation of mass. 3. describe the characteristics of a chemical reaction.

4. solve problems involving the law of definite proportions.5. evaluate compounds that conform with the law of multiple proportions.6. write chemical reactions.7. balance chemical equations.8. explain the implied information derived from a balanced equation. How to learn from this moduleHere are some helpful reminders before getting started:1. Review lessons in writing chemical symbols and formula2. Take the pretest before proceeding to the lessons.3. Perform the activities and read the discussions provided for in the lessons.4. Answer the Self-Test. Compare your answers with the keys to correction.5. Consult a dictionary if you are not sure of the meaning of some words used in this module.6. Answer the posttest so that you will know how much you have learned from the lessons.7. Keep an open mind to the new concepts you will be learning in this module. Happy reading!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 of the following is true of a chemical reaction?a. Only physical changes occur. c. Only changes of state occur.b. New substances must form. d. Chemical properties remain the same.2. A substance that enters into a chemical reaction is called aa. mole c. coefficientb. product d. reactant3. A substance that is formed by a chemical reaction is called aa. mole c. coefficientb. product d. reactant -2-

4. When oxygen is available, sulfur dioxide is produced from the burning of sulfur. Which of the following word equations best represents this reaction? a. sulfur + oxygen → sulfur dioxide c. sulfur dioxide → sulfur + oxygen b. sulfur dioxide + oxygen → sulfur d. sulfur → sulfur dioxide + oxygen5. In a chemical equation, the symbol that takes the place of the words ‘reacts with’ is a (n)a. equal sign c. plus signb. coefficient d. arrow6. Which of the following is TRUE of a balanced equation? a. The total number of atoms remains the same. b. The kinds of atoms remain the same. c. The total number of molecules remains the same. d. The number of atoms of each element remains the same.7. In a chemical equation, the number of molecules of a given substance is indicated by aa. subscript c. superscriptb. coefficient d. reaction number8. The symbol(s) written after a formula in a chemical equation stands fora. soluble c. solidb. solution d. synthesis9. What number should be written in front of Na to balance the equationNa + MgCl2 → NaCl + Mg?a. 1 c. 3b. 2 d. 4Use the diagram to answer questions 10 – 14. -H - Br10. What word equation describes the reaction in the figure above? a. Hydrogen plus bromine are formed from hydrogen bromide. b. Hydrogen plus bromine yields hydrogen plus bromine. c. Hydrogen plus hydrogen bromide yields bromine. d. Hydrogen plus bromine yields hydrogen bromide.11. What formula equation describes the reaction?a. H2 + Br2 → H2Br2 c. H2 + Br2 → HBrb. 2 H + 2 Br → 2HBr d. 2H + 2 Br → H2Br2 -3-

12. What is the balanced formula equation for the reaction shown in the figure?a. H2 + Br2 → 2HBr c. H2 + Br2 → H2Br2b. 2H + 2Br → 2HBr d. H2 + Br2 → HBr + HBr13. Identify the product(s) in the figure c. hydrogen bromide only a. hydrogen only d. both bromine and hydrogen bromide b. both hydrogen and bromine14. Identify the reactant(s) in the figure c. hydrogen bromide only a. hydrogen only d. both bromine and hydrogen bromide b. both hydrogen and bromine15. 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 proportions16. Why can’t you change the formula in order to balance a reaction? a. The number of atoms in 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.17. Which equation conforms with the Law of Conservation of Mass? a. 2Al(l) + BaO(s) → Al2O3(s) + 3Ba(l) b. CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) c. Cl2(g) + KBr(aq) → 2KCl(aq) + Br2(l) d. 2Na(s) + H2O(l) → 2 NaOH(s) + H2(g)18. Which statement conforms with the law of definite proportions? a. The mass of hydrogen is twice that of oxygen in a water molecule. b. When mixtures of gaseous H2 and gaseous Cl2 react, a product forms that has the same properties regardless of the relative amounts of H2 and Cl2 used. c. Several compounds have the same composition as long as they have the same ratios. d. Compounds have similar proportions as long as they are solid.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. -4-

d. When two elements form a series of compounds, the ratio of the second element that combines with 1g of the first element can be reduced into small whole numbers. Key to answers on page 22. If your score is 18-20 Very good. You have the option to skip the module but you are still encouraged to go through it. 14-17 Good! Go over the items that you find difficult and then you may proceed to the lessons in this module that you don’t understand 0-10 Don’t worry about your score. Read this module. This module is prepared in order for you to understand the chemical reactions. So, what are you waiting for? Your journey begins here………..Lesson 1. The Law of Conservation of Mass In the late eighteenth century, Antoine Lavoisier, a French chemist, recognized theimportance of accurate measurements. He extensively studied and explained the nature ofcombustion. He found out that combustion involved reaction with oxygen. His experiments,in which he carefully weighed the reactants and products of various reactions, suggestedthat mass is neither created nor destroyed. Lavoisier’s discovery of this law ofconservation of mass was the basis for the development in chemistry in the nineteenthcentury. A chemical change involves reorganization of the atoms in one or more substances.The law of conservation of mass requires that there must be exactly as many atoms amongthe combined products of a chemical reaction as in its combined reactants. To understandthis better, let us define words that will be used in this lesson. Reactants are the startingmaterial in a chemical reaction. Products are the substance formed as a result of achemical reaction. In a chemical equation, reactants are found on the left side and theproducts are on the right side. A chemical reaction can therefore be summarized as Reactants → Products -5-

For example, when the methane (CH4) in natural gas combines with oxygen (O2) inthe air and burns, carbon dioxide (CO2) and water (H2O) are formed. The balanced chemical equation for this reaction is: CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) The reactants in this reaction are methane and oxygen gas. The products are carbondioxide and water. A balanced equation conforms to the law of conservation of mass. Let us check if thenumber of atoms of each kind on the left side of the reaction is equal to the number ofatoms of each kind on the right side of the equation. There is 1 atom of carbon on the left side and 1 atom of carbon on the right side. There are 4 atoms of hydrogen on the left side. On the right side, there are 2 atomsof hydrogen that is multiplied by the coefficient 2 found on the left side of H2O. On the left side of the equation, there are 2 atoms of oxygen multiplied by thecoefficient 2 found on the left side of O2. On the right side, there are two atoms of oxygen inCO2 and 1 atom of oxygen in H2O multiplied by the coefficient 2 found on the left side ofH2O. To get a clearer view of the number of atoms of each kind, look at the table belowKind of Atom No. on Left side No. on Right side C 1 1 H 4 O 2x2=4 2x2=4 2 + 1(2) = 4Thus, the balanced equation above conforms to the law of conservation of mass.Let us have another example. When aluminum and barium oxide are heated together, a vigorous reaction begins,and elemental barium and aluminum oxide, Al2O3, are formed. The equation is 2Al(l) + 3BaO(s) → Al2O3(s) + 3Ba(l) a. Identify the reactants and products. b. Check the equation if it conforms with the Law of Conservation of Mass. -6-

Answer: a. The reactants are Al and BaO. The products are Al2O3 and Ba.b. Kind of Atom No. on Left side No. on Right side Al 1 x 2 = 2 2 Ba 1x3=3 1x3=3 O 1x3=3 3It conforms with the Law of Conservation of Mass. Your Turn Identify the reactants and products of the reaction. Check the equation if it conforms with the Law of Conservation of Mass. 1. Cl2(g) + 2 KBr(aq) → 2KCl(aq) + Br2(l) 2. 2Na(s) + 2H2O(l) → 2NaOH(s) + H2(g) 3. K2CrO4(aq) + 2AgNO3(aq) → Ag2CrO4(s) + KNO3(aq) Solution: a. The reactants are compounds found on the left, the products are the compounds on the right b. No. 3 does not conform with the law of conservation of mass. The equation is not balanced. Another application of the Law of Conservation of Mass in chemical reactions is topredict the mass of the products when the mass of the reactants are known. If the Law ofConservation of Mass holds, the total mass of reactants must equal the total mass of theproducts. Therefore, Total mass reacted = Total mass produced Going back to our first example, if 46.0 g of methane reacts with 96.0 g of oxygen toproduce 54.0 g water, how much carbon dioxide is produced? CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) 46.0 g + 96.0 g = Carbon dioxide + 54.0 g 142.0 g - 54.0 g = 88.0 g carbon dioxide -7-

Your Turn In the reaction shown below, 2Al(l) + 3BaO(s) → Al2O3(s) + 3Ba 65.0 g of Aluminum reacted with 35.0 g of Barium oxide to produce aluminum oxide and barium. If 84.0 g of aluminum oxide is produced, how much barium is produced? Solution: 16 g Ba What you will do Self-Test 1.1Answer the following questions.1. You have a chemical in a sealed glass container filled with air. The system has a mass of 250.0 g. The chemical is ignited by means of a magnifying glass focusing sunlight on the reactant. After the chemical is completely burned, what is the mass of the system?2. Check the following reactions if it conforms with the Law of Conservation of Mass. a. N2O5(g) → N2O4(g) + O2(g) b. 2Mg(s) + O2(g) → 2MgO(s) c. H3PO4(aq) + 3NH3(aq) → (NH4)3PO4(aq)3. Identify the reactants and products in no. 2. Key to answers on page 22.Lesson 2. Law of Definite Proportions After Lavoisier, another French scientist studied the composition of various chemicalcompounds. Joseph Proust showed that a given compound always contains exactly thesame proportion of elements by mass. The principle of the constant composition ofcompounds, originally called Proust’s Law, is also known as the Law of DefiniteProportions. Another way of stating the law is that different samples of the samecompound always contain its constituent elements in the same proportions by mass.Elements combine in fixed proportion when they form a compound. -8-

Example: A sample of chloroform, CHCl3, is found to contain 12.0 g of carbon, 106.4 g chlorine,and 1.01 g hydrogen. If a second sample is found to contain 30.0 g of carbon, how manygrams of chlorine and of hydrogen does it contain? Strategy: Using the law of definite proportions, the ratios of the weights of the elements in chloroform are constant. Therefore, we have to find the ratio of carbon and the factor must hold true for chlorine and hydrogen. Solution: a. Finding the ratio for carbon: 30.0 g/12.0 g = 2.5. The 2.5 means that carbon is increased by a factor of 2.5. Thus, it will hold true for Cl and H. b. Finding the mass for chlorine in sample 2: 106.4 (2.5) = 266 g Cl c. Finding the mass for hydrogen in sample 2: 1.01 (2.5) = 2.53 g H This law can be applied when doing chemical reactions. When there is 30.0 g ofcarbon, 300 g of Chlorine, and 3.00 g of Hydrogen to form chloroform, only 266 g of chlorineand 2.53 g of hydrogen are used up in the reaction. What you will do Activity 2.1Solve the following problems.1. A compound is composed of 23.0 g sodium and 35.0 g chlorine. If 105.0 g of chlorine is available for reaction, what mass of sodium is needed to complete the salt reaction?2. The ratio of hydrogen to chlorine is 1:35. What mass of chlorine is needed when there are 25 g of chlorine available to produce hydrochloric acid?3. Proust discovered that the substance copper carbonate is always 5.3 parts copper to 4 parts oxygen to 1 part carbon. When 60 g of copper is present in the compound, what are the masses of oxygen and carbon? Key to answers on page 22. Were you able to answer the questions in Activity 2.1? You are now ready to takethe test for this lesson. -9-

What you will do Self-Test 2.1Provide the needed answer for the following questions:1. Which statement conforms with the law of definite proportions? a. The mass of hydrogen is twice that of oxygen in a water molecule. b. When mixtures of gaseous H2 and gaseous Cl2 react, a product forms that has the same properties regardless of the relative amounts of H2 and Cl2 used. c. Several compounds have the same composition as long as they have the same ratios. d. Compounds have similar proportions as long as they are solid.2. A reaction of 1 L of chlorine gas (Cl2) with 3 L of fluorine gas (F2) yields 2 L of a gaseous product. All gas volumes are at the same temperature and pressure. What is the formula of the gaseous product?3. Sulfur and oxygen can react to form sulfur dioxide. In sample 1, there are 32.06 g of sulfur and 32.00 g of oxygen. In sample 2, there are 16.03 g of sulfur. What is the mass of oxygen in sample 2? If the sulfur in sample 1 is increased by a factor of three, what mass of oxygen is needed to complete the reaction? Key to answers on page 22.Lesson 3. The Law of Multiple Proportions Proust’s discovery inspired John Dalton, an English school teacher, to think aboutatoms. The Law of Definite Proportions explained why the same relative masses ofelements were always found in a given compound. Dalton discovered another principle. Henoted that carbon and oxygen form two different compounds that contain different relativeamounts of carbon and oxygen as shown by the following data:Compound no. 1 Mass of oxygen that combines with 1 gCompound no. 2 of carbon 1.33 g 2.66 g Dalton noted that compound 2 contained twice as much oxygen per gram of carbonas compound 1. Compound 1 might be a CO and compound 2 might be CO2. Thisphenomenon can be further explained in a backyard grilling activity. - 10 -

Imagine you are preparing grilled fish for supper. The fish is sizzling over hotcharcoal. The glowing charcoal that cooks the fish consists mostly of the element carbon. Itburns slowly with oxygen of the evening air. In the overall reaction, one atom of carboncombines with a diatomic molecule of oxygen to produce one molecule of carbon dioxide.When plenty of oxygen is available, the following reaction occurs in the grill.C(s) + O2(g) → CO2(g) When charcoal burns in an enclosed space, such as a closed room where there isn’tenough oxygen to convert all the carbon to carbon dioxide, lethal carbon monoxide, CO,forms. When there is insufficient oxygen, the reaction becomes2C(s) + O2(g) → 2CO(g) This principle, which was found by Dalton to apply to compounds of other elementsas well, became known as the law of multiple proportions. When two elements form aseries of compounds, the ratios of the masses of the second element that combine with 1gram of the first element can always be reduced to small whole numbers. These ideas are illustrated by the compounds of nitrogen and oxygen, as shown bythe following data:Compound 1 Mass of nitrogen that combines with 1 gCompound 2 of oxygenCompound 3 1.750 g 0.8750 g 0.4375 gwhich yields the following ratios:1 = 1. 750 = 22 0.8750 11 = 1.750 = 43 0.4375 1 2 = 0.8750 = 2 3 0.4375 1 The significance of these data is that compound 1 contains twice as much nitrogenper gram of oxygen as does compound 2 and that compound 1 contains four times as muchas in compound 3. Compound 2 contains twice as much as compound 3. In terms of thenumber of atoms combining, these are some of the possible sets of formulas: - 11 -

Compound 1 First Series Second Series Third SeriesCompound 2 N2O NO N4O2Compound 3 NO NO2 N2O2 NO2 NO4 N2O4Your Turn1. Sulfur and oxygen can react to form both sulfur dioxide and sulfur trioxide. In sulfur dioxide, there are 32.06 g of sulfur and 32.00 g of oxygen. In sulfur trioxide, 32.06 g of sulfur are combined with 48.00 g of oxygen. a. What is the ratio of the weights of oxygen that combine with 32.06 g of sulfur? b. How do these data illustrate the law of multiple proportions?2. Several compounds containing only sulfur (S) and fluorine (F) are known. Two of them have the following compositions: i. 1.188 g of F for every 1.000 g of S ii. 2.375 g of F for every 1.000 g of S a. What is the ratio of the two Fluorine samples? b. What are the possible formulas for the two compounds?Solution: 1. a. The ratio is 1.5 to 1 or 3 to 2. b. The ratios are two whole numbers. 2. a. The ratio is 1 is to 2. b. F2S, F2S2What you will doSelf-Test 3.1Answer the following questions.1. Which set of compounds illustrates the law of multiple proportions?a. CH4, CO, CCl4 c. NaCl, NaBr, NaIb. N2O, NO, NO2 d. HF, F2S, FCl3 - 12 -