Chapter 71 Periodic Properties of the Elements Chapter 7 2 Development of the Periodic Table -Mendeleev and Meyer arranged the elements in order of increasing atomic weight. -Arrange elements to reflect the trends in chemical and physical properties. -Modern periodic table: arrange elements in order of increasing atomic number. Chapter 73 Development of the Periodic Table Chapter 74 Electron Shells and the Sizes of Atoms -Elements in the same column have the same electron configuration. Consider:Ne: 1s 2 2s 2 2p 6 Ar: 1s 2 2s 2 2p 6 3s 2 3p 6 Both elements have the same electron configuration: [Element]ns 2 np 6 -Therefore, the elements in the periodic table should exhibit regular variations in there physical properties. Electron Shells in Atoms Chapter 75 Electron Shells and the Sizes of Atoms -Atomic size varies consistently through the periodic table. -As we move down a group, the atoms become larger. -As we move across (left to right) a period, atoms become smaller. -There are two factors at work: -principal quantum number, n -the effective nuclear charge, z eff Atomic Sizes Chapter 76 Electron Shells and the Sizes of Atoms -As the principle quantum number increases, the distance of the outermost electron from the nucleus becomes larger. Hence, the atomic radius increases. - As we move across the periodic table, there is an increased attraction between the nucleus and the outermost electrons. This attraction causes the atomic radius to decrease. Atomic Sizes Chapter 77 Electron Shells and the Sizes of Atoms Atomic Sizes Chapter 78 Ionization Energy First Ionization Energy - The first ionization energy, I 1, is the amount of energy required to remove an electron from a gaseous atom: Na(g) Na + (g) + e - -The larger ionization energy, the more difficult it is to remove the electron. -There is a sharp increase in ionization energy when a core electron is removed. Chapter 79 Ionization Energy Chapter 710 Ionization Energy -Ionization energy decreases down a group. -As the atom gets bigger, it becomes easier to remove an electron from the most spatially extended orbital. - Ionization energy generally increases across a period. -Two exceptions: removing the first p electron and removing the fourth p electron have a lower energies. -This indicates that half-filled and completely filled subshells are more stable. Periodic Trends in Ionization Energy Chapter 711 Ionization Energy -The s electrons are more effective at shielding than p electrons. Therefore, forming the s 2 p 0 becomes more favorable. -When a second electron is placed in a p orbital, the electron-electron repulsion increases. When this electron is removed, the resulting s 2 p 3 is more stable than the starting s 2 p 4 configuration. Periodic Trends in Ionization Energy Chapter 712 Ionization Energy Periodic Trends in Ionization Energy Chapter 713 Electron Affinities Electron affinity The energy required to add an electron to an atom in the gaseous state: Cl(g) + e - Cl - (g) -Electron affinity can either be exothermic (as the above example) or endothermic. -The added electron in Cl is placed in the 3p orbital to form the stable 3p 6 electron configuration. Chapter 714 Electron Affinities Chapter 715 Metals, Nonmetals, and Metalloids Metal character refers to the properties of metals - Shiny luster - Malleable - Ductile - Oxides form basic ionic solids - Tend to form cations in aqueous solution Metals Chapter 716 Metals, Nonmetals, and Metalloids Chapter 717 Metals, Nonmetals, and Metalloids -Metal character increases down a group. -Metal character decreases across a period. Metals Chapter 718 Metals, Nonmetals, and Metalloids -When metals are oxidized metals form cations. -All group 1A metals form M + ions. -All group 2A metals form M 2+ ions. -Most transition metals have variable charges. Metals Chapter 719 Metals, Nonmetals, and Metalloids Metals Chapter 720 Metals, Nonmetals, and Metalloids -Most metal oxides are basic: Metal oxide + water metal hydroxide Na 2 O(s) + H 2 O(l) 2NaOH(aq) Metals Chapter 721 Metals, Nonmetals, and Metalloids -When nonmetals react with metals, nonmetals tend to gain electrons: metal + nonmetal salt 2Al(s) + 3Br 2 (l) 2AlBr 3 (s) -Most nonmetal oxides are acidic: nonmetal oxide + water acid P 4 O 10 (s) + H 2 O(l) 4H 3 PO 4 (aq) Nonmetals Chapter 722 Metals, Nonmetals, and Metalloids -Metalloids have properties that are intermediate between metals and nonmetals. Metalloids Chapter 723 Metals, Nonmetals, and Metalloids -Metalloids have properties that are intermediate between metals and nonmetals. Example: Si has a metallic luster but it is brittle. Metalloids Chapter 724 Group Trends for the Active Metals -Alkali metals are all soft. -Chemistry dominated by the loss of their single s electron: M M + + e -Reactivity increases as we move down the group. -Alkali metals react with water to form MOH and hydrogen gas: 2M(s) + 2H 2 O(l) 2MOH(aq) + H 2 (g) Group 1A: The Alkali Metals Chapter 725 Group Trends for the Active Metals -Alkali metal produce different oxides when reacting with O 2 : 4Li(s) + O 2 (g) 2Li 2 O(s)(oxide) 2Na(s) + O 2 (g) Na 2 O 2 (s)(peroxide) K(s) + O 2 (g) KO 2 (s)(superoxide) Group 1A: The Alkali Metals Chapter 726 Group Trends for the Active Metals Group 1A: The Alkali Metals -Alkali metals emit characteristic colors when placed in a high temperature flame. Chapter 727 Group Trends for the Active Metals Group 1A: The Alkali Metals Na Li K -Alkali metals emit characteristic colors when placed in a high temperature flame. Chapter 728 Group Trends for the Active Metals -Alkaline earth metals are harder and more dense than the alkali metals. -The chemistry is dominated by the loss of two s electrons: M M e -. -Chemical reactivity increases as you move down the group. - Be does not react with water at any temperature. - Mg will only react with steam. - Ca onwards: Ca(s) + 2H 2 O(l) Ca(OH) 2 (aq) + H 2 (g) Group 2A: The Alkaline Earth Metals Chapter 729 Group Trends for Selected Nonmetals -Hydrogen is a unique element. -Most often occurs as a colorless diatomic gas, H 2. -It can either gain another electron to form the hydride ion, H , or lose its electron to become H + : 2Na(s) + H 2 (g) 2NaH(s) 2H 2 (g) + O 2 (g) 2H 2 O(g) -H + is also called a proton. -The aqueous chemistry of hydrogen is dominated by H + (aq). Hydrogen Chapter 730 Group Trends for Selected Nonmetals -As we move down the group the metallic character increases (O 2 is a nonmetal, Te is a metalloid, Po is a metal). -There are two important forms of oxygen: -O2-O2 -O 3, ozone. 3O 2 (g) 2O 3 (g) H = kJ. -Oxygen (or dioxygen, O 2 ) is a potent oxidizing agent. -There are two oxidation states for oxygen: -2 (H 2 O) and -1 (H 2 O 2 ). Group 6A: The Oxygen Group Chapter 731 Group Trends for Selected Nonmetals -Sulfur is another important member of this group. -Most common form of sulfur is yellow S 8. -Sulfur tends to form S 2- in compounds (sulfides). Group 6A: The Oxygen Group Chapter 732 Group Trends for Selected Nonmetals -The chemistry of the halogens is dominated by gaining an electron to form an anion: X 2 + 2e - 2X - -Fluorine is one of the most reactive substances known. -All halogens consists of diatomic molecules, X 2. Group 7A: The Halogens Chapter 733 Group Trends for Selected Nonmetals -Chlorine is the most industrially useful halogen. It is produced by the electrolysis of brine (NaCl): 2NaCl(aq) + 2H 2 O(l) 2NaOH(aq) + H 2 (g) + Cl 2 (g) -The reaction between chlorine and water produces hypochlorous acid (HOCl) which disinfects pool water: Cl 2 (g) + H 2 O(l) HCl(aq) + HOCl(aq) -Hydrogen compounds of the halogens are all strong acids with the exception of HF. Group 7A: The Halogens Chapter 734 Group Trends for Selected Nonmetals -These are all nonmetals and monatomic. -They are unreactive because they have completely filled s and p sub-shells. -In 1962 the first compound of the noble gases was prepared: XeF 2, XeF 4, and XeF 6. Group 8A: The Noble Gases Chapter 735 Homework: 7.8, 7.18, 7.30, 7.32, 7.42, 7.52, 7.60, 7.68, 7.70