2 size increases down a group increasing principal

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2 Size increases down a group. Increasing principal quantum number, n , of valence orbitals means larger orbitals and an increase in atom size. P. J. Grandinetti (Chem. 4300) Multi-electron Atoms Nov 20, 2017 17 / 39
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Ionization Energy Amount of energy required to remove an e - from gaseous atom or ion is called ionization energy . First ionization energy, I 1 , is energy required to remove highest energy e - from neutral gaseous atom. Na(g) Na + (g) + e - I 1 = 496 kJ/mol . Ionization energy is positive because it requires energy to remove e - . Second ionization energy, I 2 , is energy required to remove 2nd e - from singly charged gaseous cation. Na + (g) Na 2 + (g) + e - I 2 = 4560 kJ/mol . Second ionization energy is almost 10 times that of 1st because number of e - s causing repulsions is reduced. Third ionization energy, I 3 , is energy required to remove 3rd electron from doubly charged gaseous cation. Na 2 + (g) Na 3 + (g) + e - I 3 = 6913 kJ/mol . P. J. Grandinetti (Chem. 4300) Multi-electron Atoms Nov 20, 2017 18 / 39
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Ionization Energy 3rd ionization energy is even higher than 2nd. Successive ionization energies increase in magnitude because number of e - s, which cause repulsion, steadily decrease. Not a smooth curve. Big jump in ionization energy after atom has lost valence electrons. Atom that has same electronic configuration as noble gas is really going to hold on to its e - s. Amount of energy needed to remove e - s beyond valence electrons is significantly greater than energy of chemical reactions and bonding. Only valence electrons (i.e., e - s outside of noble gas core) are involved in chemical reactions. P. J. Grandinetti (Chem. 4300) Multi-electron Atoms Nov 20, 2017 19 / 39
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1st ionization energy 10 0 20 30 40 50 500 0 1000 1500 2000 2500 atomic number first ionization energy / kJ/mol Period 1 Period 2 Period 3 Period 5 Period 6 Li Be Be B C O F Cl Ne Kr Na Mg Mg Al Si P S He He H N N Ar 1st ionization energies generally increase as atomic radius decreases. Two clear behaviors are observed: 1st ionization energy increases across period. The first ionization energy decreases down a group. P. J. Grandinetti (Chem. 4300) Multi-electron Atoms Nov 20, 2017 20 / 39
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1st ionization energy 1st ionization energy increases across period. Because e - in same principal quantum shell do not completely shield increasing nuclear charge of protons. e - s are held more tightly and require more energy to be ionized. e.g., I 1 ( Cl ) > I 1 ( Na ) and I 1 ( S ) > I 1 ( Mg ) . Plot of ionization energy versus atomic number is not perfect line as there are easily explained exceptions to rules. Filled and half-filled subshells show small increase in stability in same way that filled shells show increased stability. When trying to remove e - from one of these filled or half-filled subshells, slightly higher ionization energy is found. e.g., I 1 ( Be ) > I 1 ( B ) . It is harder to ionize e - from Be than B because Be has filled s sub-shell. e.g., I 1 ( N ) > I 1 ( O ) . N has half-filled 2p sub-shell so it is harder to ionize e - from N than O.
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