electron configurations nuclear charge Periodic Properties properties electron configurations nuclear charge hydrogen atom 1 electron 1s1 Z = 1 1 1 to remove e- nf = ∞ E = - RH Z2 - nf2 ni2 from ground state ni = 1 E = 2.178 x 10-18 J x 6.022 x 1023 atoms = 1311 kJ atom mol mol Ionization Energy, I

systems with more than 1 electron Z = +1 E = 1311 kJ/mol He+ 1s1 Z = +2 E = 5250 kJ/mol - - + 2+ 1 1 = 5250 kJ/mol E = - RH Z2 - nf2 ni2 higher nuclear charge lowers orbital energy stabilizes system systems with more than 1 electron studied experimentally ionization reactions

Effect of 2 electrons in same orbital 1. Effect of 2 electrons in same orbital He+ 1s1 E = 5250 kJ/mol He 1s2 E = 2372 kJ/mol Z = +2 same nuclear charge orbital energy higher - 2+ - e- e- repulsion 2+ - less stable easier to remove e-

Effect of electrons in different orbital 2. Effect of electrons in different orbital Li ground state 1s2 2s1 E = 520 kJ/mol Li2+ excited state 2s1 E = 2954 kJ/mol Z = +3 same nuclear charge 2s 2s 1s 1s - - - 3+ 3+ - Zeff < Z inner electrons shielding charge

Effect of orbital shape 3. Effect of orbital shape Li ground state 1s2 2s1 E = 520 kJ/mol Li excited state 1s2 2p1 E = 341 kJ/mol Z = +3 same nuclear charge 2s 2p 1s 1s - - - - 3+ 3+ - - s orbitals penetrating lower energy

Electrostatic interactions determine orbital energies 1. Greater nuclear charge (Z) lowers energy electrons more difficult to remove 2. Electron-electron repulsion raise energy electrons easier to remove electrons shield Z inner electrons shield better 3. Orbitals with more penetration lower 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+(g) + e- first ionization energy I1 X+ (g)  X2+(g) + e- second ionization energy I2 lowest I1 Cs n = 6 highest I1 He n = 1

I1 increase Z increases shielding stays same adding valence e- core e- unchanged I1 decrease Zeff decreases more shielding e- core e-

2p 2p - - 2s 2s 1s 1s - - - - - - - 5+ 10+ - - - - - - B Ne

2p - 2s 2s 1s 1s - - - - - 4+ 5+ - - - B Be N O e- e- repulsion

Second Ionization Energy Na 495 4560 Mg 735 1445 7730 Al 580 1815 11,600 Si 780 1575 16,100 P 1060 1890 21,200 S 1005 2260 27,000 very difficult to remove Cl 1255 2295 core electrons Ar 1527 2665

Atomic Radius metallic radius Al 143 pm Cl 100 pm covalent radius C-Cl 177 pm Cl 100 pm 77 pm C

Atomic Radius increase in size n dominates decrease in size Zeff dominates

Ionic sizes isoelectronic series same # electrons 46 e- + isoelectronic series same # electrons 46 e- +49 +50 +51 ions get smaller