Group 13: The Boron Family

ns2np1

Atomic properties

• All have +3 oxidation state except Tl

• +1 state becomes more common down the group

• Smaller atomic size than Group 2

• Lower IE than Group 2

• Higher EN than Group 2

  • because it is easier to remove an electron from the higher energy p sublevel

• Atomic size, EN, and IE do not change as expected down the group because there are intervening transition and inner transition elements

Physical properties

• Bonding changes from network covalent in B to metallic in the rest of the group

  • Thus, B has a higher melting point

• Boiling points decrease down the group

• Densities increase down the group

Boron

• Metalloid, usually forms compounds that are electron deficient

• Much less reactive at room temp than other members and forms covalent bonds exclusively

Aluminum

• Most abundant metal in the Earth’s crust, elemental form does not occur in nature

• Can only be obtained through the Hall-Heroult process, an industrial process used to produce aluminum

  • Involves electrolyzing molten salt bath of Cryolite to alumina then extracting pure aluminum from the alumina

• Aluminum oxides are amphoteric (both acidic and basic)

Reactions

• All members react with O2 (g) to make oxides
• Oxide acidity decreases down the group
• All members reduce halogens

Acidity vs Basicity of the Oxides

• B: B2O3 (s) + 6 NaOH (aq) → 2 Na3BO3 (aq) + 3 H2O (l)
  (cf. HCl (g) + NaOH (aq) → NaCl (aq) + H2O(l) )
  in water, forms B(OH)3 (or H3BO3), known as boric acid.
  B(OH)3 + 2 H2O ⇌ B(OH)4- + H3O+ pKa = 9.25

• Al, Ga: oxides react with bases as above, but also with acids. They are “amphoteric” (= can behave as both acids or bases)

  Al2O3 (s) + 6 NaOH → 2 Na3AlO3 (aq) + 3 H2O (l)

  Al2O3 (s) + 3 H2SO4 (l) → Al2(SO4)3 (s) + 3 H2O (l)

• In, Tl: oxides are basic and react only with acids.
  In2O3 (s) + 3 H2SO4 (l) → In2(SO4)3 (s) + 3 H2O (l)