Trends in chemical reactivity of group 13 elements

The important trends observed in the chemical behavior of group 13 elements are

1. Group 13 elements form hydrides of the type MH3. Thermal stability of hydrides decreases as we move down the group. Hydrides act as weak lewis acids. Boron forms a number of hydrides known as boranes. The important series among boranes are nido-boranes (BnHn+4) and arachno-boranes (BnHn+6). Aluminium and Galium can form tetra hydrido anions (MH4-).[LiAlH4] is an example for this and is a good reducing agent used in organic synthesis.

2. The elements of group 13 form trihalides of the type MX3. The trihalides are strong Lewis acids. The flurides are ionic and have high melting points. The chlorides, bromides and iodides are covalent compounds with low melting points. Halides can exist in dimeric form with halogen bridges.

3. All the elements of group 13 form oxides with formula M2O3 and hydroxides of the type M(OH)3. Basic character of oxides and hydroxides increases as we move down the group.

4. Due to the presence of d-orbitals Aluminum, Gallium, Indium and Thallium can form octahedral complexes (eg: [AlF3]3-) and octahedral aqua ions, [M(OH2)6]3+. Because of small size and increased nuclear charge, many salts like halides, sulphates, nitrates and perchlorates exist as hydrates. Aluminum sulphate forms double salts with other sulphates of monovalent metals and are called alums, having general formula MAl(SO4)2.12H2O, where M is univalent cation like Na+ or K+. Alums are used for softening hard water and used as mordant.

Group 13 elements and their nature

1. Boron

Oxide - B2O3
Hydroxide - B(OH)3
Nature - Weakly acidic

2. Aluminum

Oxide - Al2O3
Hydroxide - Al(OH)3
Nature - Amphoteric

3. Gallium

Oxide - Ga2O3
Hydroxide - Ga(OH)3
Nature - Amphoteric

4. Indium

Oxide - In2O3
Hydroxide - In(OH)3
Nature - Basic

Related chemistry article Trends in chemical properties of group 17 elements

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