Group IV Tetrahalides

Group IV Tetrahalides

1. Covalent molecular compounds with a tetrahedral shape.

Only PbF4 and SnF4 are appreciably ionic. Most compounds will therefore have low melting and boiling points.

CF4, SiF4 and GeF4 are all gases. Most chlorides and bromides are liquids and most iodides are solids.

2. Thermal stability decreases down the group. This results in weaker and longer M-X bonds.

3. Hydrolysis: they are all hydrolysed by water except for CCl4. Hydrolysis results in the evolution of HCl .

SnCl4(l) + 2H2O(l) → Sn(OH)4(aq)

PbCl4 is very rapidly hydrolysed. A stepwise mechanism is proposed for the hydrolysis. H2O molecules donate their lone pair of electrons to vacant d orbitals on the central atom causing the stepwise displacement of Cl- ions.

Mechanism:

Why is CCl4 not hydrolysed?

All but carbon are able to use vacant d orbitals to allow the water ligands to donate their lone pairs required for hydrolysis to take place.

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