Ionization Energy and Electron Affinity Section

Objectives Examine periodic trends in ionization energy Examine periodic trends in electron affinity

Key Terms Ionization energy Electron Affinity

Ionization Energy Ease at which electrons can be removed from an atom or ion First ionization energy, I 1, is the energy required to remove the first electron from neutral atom Second ionization energy, I 2, is the energy required to remove the second electron from a +1 ion Greater the I, the more difficult to remove the electron

Trends of Ionization Energy I 1 < I 2 < I 3 < I 4 With each removal, the ion becomes more positive Strengthens nucleus’s hold on its electrons Sharp increase in I when inner-shell electrons are removed Table 7.2 on page 271

Periodic Trends in I 1 Within rows, I 1 increases with atomic number Slight irregularities Within columns, I 1 decreases with increasing atomic number Representative elements show larger range of I 1 values than transition metals Transitions slowly increase across rows

Factors Affecting Trends More energy is needed to remove an electron as: Effective Nuclear Charge increases Atomic Radius decreases

Irregularities I does not always increases across rows Decrease from Be to B Be: [He] 2s 2 B: [He]2s 2 2p 1 The most easily removed electron in B is that in the 2p orbital, higher in energy than the 2s electrons in Be 2p electron of B needs less energy for total removal than does the 2s electron of Be

Irregularities O is lower than N N: [He]2s2 2p3 O: [He]2s2 2p4 Important difference in the way electrons are distributed Hund’s rule: 3 e- in the 2p orbitals of a nitrogen atom all have the same spin, but e- are paired in one of the 2p orbitals of oxygen Electrons try to stay as far apart as possible to minimize repulsion Force of repulsion between these electrons is minimized to some extent by pairing electrons Slightly easier to remove an electron

Electron Affinities Energy change that occurs when electron are added to a gaseous atom Measure of the attraction of an atom to an electron Negative values (energy is released during process) kJ/mol More negative affinity = greater attraction

Trends in Affinities Not as evident as that of ionization energy Halogens have the greatest affinities (1 e- shy of a filled p subshell) Noble gases have affinities of 0 Group 2A and 5A have very little affinity

Electron Affinities (kJ/mol)

Putting it all together

Homework 7.35, 7.42, 7.44, and 7.46 on page 294