1 CHEMISTRY 161 Chapter 8 Periodic Relationships Among the Elements

2 MAIN GROUPS ATOMIC RADIUS REVISION ATOMIC RADIUS

3 PERIODIC TRENDS 3. IONIZATION ENERGIES 4. ELECTRON AFFINITIES 1. ATOMIC RADIUS 2. IONIC RADIUS

4 3. IONIZATION ENERGIES M(g)  M + (g) + e - energy required to remove an electron from a gas phase atom in its electronic ground state I 1 > 0 first ionization energy (photon)

5 M + (g)  M 2+ (g) + e - M 2+ (g)  M 3+ (g) + e - second ionization energy third ionization energy I 2 > 0 I 3 > 0 I 1 > I 2 > I 3

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7 Why? electrons closer to nucleus more tightly held Z eff DECREASES IONIZATION ENERGY first ionization energies decrease d shell insertion

8 Z eff INCREASES IONIZATION ENERGY

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10 1. closed shells are energetically most stable 2. half-filled shells are energetically very stable DERIVATION OF IONIZATION ENERGIES

11 noble gases have the highest ionization energy

12 4. ELECTRON AFFINITIES the energy change associated with the addition of an electron to a gaseous atom X(g) + e –  X – (g) electron affinity can be positive or negative

13 Why? ELECTRON AFFINITY general trend

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15 1. closed shells are energetically most stable 2. half-filled shells are energetically very stable DERIVATION OF ELECTRON AFFINITIES

16 SUMMARY

17 Homework Chapter 8 pages , problem sets