Trends of P.T.

Atomic radius: measured as ½ distance betw. 2 nuclei of like atoms in molecule or crystal (T-46)

Two factors affect:   Z_eff (= Z – avg. e^-)

n (energy level)

       Z_eff ↑ size¯                       n ↑ size ↑

                                                        (Greater effect)

· ¯ as move left to rt across period (increased Z_eff)

· as move down column of table (increased n)

The experimental As-I bond length in arsenic Triiodide, AsI₃, is 2.55 Ǻ.  How close is this value to the one predicted by using the atomic radii of the elements?

Ionization energy: min. energy required to REMOVE e- from atom (T-47, 48, 49)

I₁ = Mg  à                               E = 738 kJ/mol

I₂ =                                          E = 1450 kJ/mol

I₃ =                                          E = 7730 kJ/mol

· as move left to rt across period (increased Z_eff)

· ¯ as move down column (increased n)

Electron Affinity: energy change when e- added to gaseous atom (measure of attraction for e-)

+ energy (add energy to gain e-, low attraction)

       (noble gases, Be, Mg, N)

Ar(g)    +      e^- à   Ar^- (g)           Δ E > 0

- energy (release energy to gain e-, high attract)

       (most atoms)

Cl (g)     +     e^- à     Cl^- (g)           Δ E -349 kJ/mol

Generally, (T-50)

· Nonmetals greater affinity (more negative)

· Metals: less affinity (less negative)