Periodic Properties electron configurations properties hydrogen atom1 electron to remove e - n f = ∞  E = x x atoms atommol = 1311 kJ mol Z = 1 from ground staten i = x J  E = 1 nf2nf2 - 1 ni2ni2 - R H Z2Z2 nuclear charge 1s11s1 Ionization Energy, I

He + Z = +2  E = 1 nf2nf2 - 1 ni2ni2 - R H Z2Z2 = 5250 kJ/mol 1s11s1  E = 5250 kJ/mol systems with more than 1 electron studied experimentallyionization reactions higher nuclear chargelowers orbital energy stabilizes system H1s11s1 Z = +1  E = 1311 kJ/mol

1.Effect of 2 electrons in same orbital He 1s21s2 Z = +2  E = 2372 kJ/mol same nuclear charge orbital energy higher e - e - repulsion less stable easier to remove e - He + 1s11s1  E = 5250 kJ/mol

2.Effect of electrons in different orbital Li Li 2+ 1s21s2 2s12s1 Z = +3  E = 2954 kJ/mol  E = 520 kJ/mol same nuclear charge 3+ ground state2s12s1 excited state 1s1s 1s1s 2s2s2s2s inner electrons shielding charge Z eff < Z

3.Effect of orbital shape Li 1s21s2 1s21s2 Z = +3  E = 341 kJ/mol  E = 520 kJ/mol same nuclear charge ground state2s12s1 excited state2p12p1 3+ 1s1s 2s2s 1s1s 2p2p s orbitals penetratinglower energy

determine orbital energiesElectrostatic interactions 1. Greater nuclear charge (Z) lowers energy 2.Electron-electron repulsionraise energy electrons more difficult to remove electrons easier to remove electrons shield Z inner electrons shield better 3.Orbitals with more penetrationlower energy electrons more difficult to remove s < p < d < f

Ionization Energy energy required to remove an e - from gas phase atoms X + (g)  X 2+ (g) + e - first ionization energy I 1 X (g)  X + (g) + e - second ionization energy I 2 lowest I 1 Cs n = 6 highest I 1 He n = 1

I 1 decreaseZ eff decreasesmore shielding e - I 1 increaseZ increases shielding stays same core e - adding valence e - core e - unchanged

5+ 1s1s 2s2s 2p2p s1s 2s2s 2p2p BNe

4+ 1s1s 2s2s Be B 5+ 1s1s 2s2s 2p2p - - N O e - e - repulsion

Second Ionization Energy I2I2 Na I1I1 I2I2 I3I3 I4I4 I5I5 I6I6 I7I7 Mg Al Si P S Cl Ar ,600 16,100 21,200 27,000 very difficult to remove core electrons

Atomic Radius metallic radius Al 143 pm covalent radius Cl 100 pm C-Cl177 pm Cl100 pm C 77 pm

Atomic Radius increase in size n dominates decrease in size Z eff dominates

Ionic sizes e-e- + - isoelectronic series 46 e ions get smaller same # electrons