Question

The coordination number of Al in the crystalline state of $AlC{{l}_{3}}$ is:

Answer 1

The number of atoms surrounded around the metal atom is called coordination number. Coordination number of some metals is going to change with the physical state of the compound. The coordination number of the central metal in liquid state is different from the coordination of the central metal atom in solid state.

Complete Solution :
- In the question it is given the coordination number of aluminium in the crystalline state of aluminum chloride.
- We have to know the structure of the crystalline aluminium chloride to know about the coordination number of aluminum.
- The structure of the aluminum chloride in liquid state is different from the structure of the aluminium chloride in crystalline state.
- The structure of the aluminium chloride in liquid state is as follows.

- In liquid state aluminium chloride exists as dimer and from the above structure the coordination number of aluminium is 4 in aluminium chloride.
- Coming to the structure of the aluminium chloride in crystalline state and it as follows.

- From the above structure we can say that the coordination number of aluminium in aluminium chloride is 6.
- Therefore the coordination of aluminium in crystalline aluminium chloride is 6.

Note: In solid state or crystalline state the chloride ions form a space lattice with aluminium ions by occupying the octahedral voids. Therefore the coordination number of aluminium in crystalline aluminium chloride is 6.