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Chemistry Unit 4: The Periodic Table and Periodic Trends (Periodicity) Background on the Periodic Table Dmitri Mendeleev: given credit for Periodic Table (~1870) -- organized Table by increasing atomic mass -- left spaces and predicted properties of undiscovered elements • put elements in order of increasing atomic number ______________. Mendeleev Regions of the Table metals: left side of Table(1-3 valence e-); form cations properties: •lustrous (shiny) •ductile (can pull into wire) •good conductors (heat and electricity) •hard •malleable (can hammer into shape) Regions of the Table (cont.) nonmetals: right side of Table(5-7 valence e; form anions by gaining electrons properties: good insulators, poor conductors gases or brittle solids dull neon sulfur iodine bromine Ne S8 I2 Br2 Regions of the Table (cont.) metalloids (semimetals): “stair” between metals and nonmetals (B, Si, Ge, As, Sb, Te, At) metals computer chips properties: (intermediate)in-between those of metals and nonmetals; “semiconductors” Si and Ge computer chips Periodicity there are trends in properties of elements -- left-right AND up-down trends atomic radius: the size of a neutral atom …increases as we go WHY? add a new energy level each time …decreases as we go WHY? it has to do with… Increase in nuclear charge Atomic Radii IA IIA IIIA IVA VA VIA VIIA Li Be B C N O F 1.52 1.11 0.88 0.77 0.70 0.66 0.64 Na Mg Al Si P S Cl 1.86 1.60 1.43 1.17 1.10 1.04 0.99 K Ca Ga Ge As Se Br 2.31 1.97 1.22 1.22 1.21 1.17 1.14 Rb Sr In Sn Sb Te I 2.44 2.15 1.62 1.40 1.41 1.37 1.33 Cs Ba Tl Pb Bi 2.62 2.17 1.71 1.75 1.46 = 1 Angstrom ionic radius: the size of an ion cations Ca atom anions Ca2+ ion Cl atom Cl1– ion 20 p+ 20 p+ 17 p+ 17 p+ 20 e– 18 e– 17 e– 18 e– Cl Cl1– Ca Ca2+ cations lose electronssmaller Anions gain electrons larger IA Atomic Radii Li 1.52 Na 1.86 K 2.31 Rb 2.44 Cs Ionic Radii IIIA IVA Be B C 0.88 0.77 Al Si 1.60 1.43 1.17 Ca 1.97 Ga Ge 1.22 Sr 1.11 Mg VA VIA VIIA N O F 0.70 P 0.66 S 0.64 Cl 1.10 1.04 0.99 As Se Br 1.22 1.21 1.17 1.14 In Sn Sb Te 2.15 1.62 1.40 1.41 I 1.33 Ba Tl Pb Bi 1.71 1.75 1.46 2.62 2.17 Li1+ Be2+ 0.60 Na1+ 0.31 0.95 0.65 K1+ Cations: smaller than parent atoms IIA Mg2+ Ca2+ N31.71 Al3+ 0.50 Ga3+ 1.33 Rb1+ 0.99 Sr2+ 0.62 1.48 Cs1+ 1.13 Ba2+ 0.81 Tl3+ 1.69 1.35 0.95 In3+ 1.37 O21.40 F11.36 S21.84 Cl11.81 Se2- Br1- 1.98 1.85 Te2- I1- 2.21 2.16 = 1 Angstrom Anions: LARGER than parent atoms ionization energy: the energy required to remove an e– from an atom Each successive ionization requires more energy than the previous one. As we go , 1st I.E…. decreases. (due to the shielding effectincrease in the number of energy levels) As we go , 1st I.E…. increases. •Nonmetals tend to gain therefore having a high first ionization energy. •Metals tend to lose-low first ionization energy electronegativity: the tendency for a bonded atom to attract e– to itself As we go , electronegativity… decreases. As we go , electronegativity… increases. •Nonmetals tend to gain therefore having a high electronegativity. •Metals tend to lose-low electronegativity Reactivity of Metals • Increases down a column – Reasons: Size (value of n), low ionization energy, and the shielding effect • Decreases left to right across a period – Reasons: Stronger nuclear charge and Increase in ionization energy Reactivity of Nonmetals • Increases left to right across a period – Why? • Smaller in size • Stronger nuclear charge • Increased ionization energy • Decreases down a column – Why? • Decreased electronegativity • Larger in size Reactivity Overview • Fr-most reactive metal • F-most reactive nonmetal • Exception: Elements with halffilled sublevels are more stable than those with empty orbitals