Chemistry 101; The Periodic Table

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About Us Welcome to Chemistry 101's Periodic Table Series, wherein we explore the various aspects of one of the most significant resources in all of science; The Periodic Table.Today we will examine the four trends that co-exist in the periodic table; reactivity, ionization energy, electronaffinity and electronegativity. However, before we embarkupon this intriguing journey, it essential that we review the basic concepts of the periodic table.PeriodicTable CheatSheet > The periodic table was published by Dmitri Mendeleev in February of 1869 > After discovering that the chemical and physical properties of elements were related to their atomic mass, Mendeleev arranged the 63 known elements in such a way that elements with similar properties would fit into columns > Today the periodic table contains approximately 108-109 elements > These elements are now arranged based on both their atomic number and mass ImportantTerms~PERIOD -- Row on the periodic table~GROUP -- Column on the periodic table~ATOMIC MASS-- Sum of protons and neutrons in anatom~ATOMIC NUMBER -- Number of protons in an atom~ TREND -- Specific pattern present in the periodic table

REACTIVITYThe tendency of a substance to undergo a chemical change. Metals A substance which readily loses electrons to form positive ions (cations). DOWN A GROUP; -- The reactivity increases -- The electrons move further away from the nucleus due to the increase in the number of energy levels-- Thus, electrons are weakly held, and easier to remove ACROSS A PERIOD; -- The reactivity decreases -- The electrons are held tightly by the nucleus due to the increase in the number of protons -- Thus, making it harder for the element to remove electrons Non-Metals A substance which wants to gain electrons to form negative ions (anions) DOWN A GROUP; -- The reactivity decreases -- The electrons move further away from the nucleus due to the increase in the number of energy levels -- Thus, making it harder for the elements to hold onto and gain electrons ACROSS A PERIOD; -- The reactivity increases -- The electrons are held tightly by the nucleus due to the increase in the number of protons -- Thus, making it easier for elements to engage in a vigorous exchange of electrons

IonizationEnergy The amount of energy required to remove an electron. DOWN A GROUP; - The ionization energy decreases - Electrons move further away from the nucleus due to an increase in the number of energy levels - As more electrons are between the nucleus and valence electrons, there is a surge in the shielding effect - Thus, less energy is required to remove electrons ACROSS A PERIOD; -- The ionization energy increases -- The electrons are held tightly by the nucleus due to the increase in the number of protons -- Elements are also closer to attaining a stable outer shell configuration, and are unwilling to lose an electron -- Thus, more energy is needed to remove an electron Electron AffinityThe measure of energy released when an electron is added to a neutral atom. DOWN A GROUP; - The electron affinity decreases - Electrons move further away from the nucleus due to an increase in the number of energy levels - As more electrons are between the nucleus and valence electrons, there is a surge in the shielding effect - Thus, less energy is released when an electron is added as the nucleus is not heavily attracted to it ACROSS A PERIOD; -- The ionization energy increases

-- The electrons are held tightly by the nucleus due to an increase in the number of protons -- As you move across the periodic table, the elements are eager to gain an electron, in order to obtain a stable outer shell configuration -- Thus, more energy is released when an electron is added ElectronegativityMeasure of an atom's tendency to attract and form bonds with electrons. DOWN A GROUP; - The electronegativity decreases - Electrons move further away from the nucleus due to an increase in the number of energy levels - As more electrons are between the nucleus and valence electrons, there is a surge in the shielding effect - The decrease in attraction is why the elements do not engage in a vigorous exchange of electrons ACROSS A PERIOD; -- The electronegativity increases -- Added electrons can be held more tightly by the nucleus due to the increasing number of protons and decreasing atomic size -- Thus, allowing the elements on the right side of the periodic table to engage in a vigorous exchange of electrons

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