75.CHEMICAL BONDING (22)- Covalent Bonding(21)- Hybridization in solid state

How compounds exist in solid state ?

Compounds exist as ions in solid state. Consider the following example –  

PCl₅ molecule – This molecule has trigonal bipyramidal (TBP) geometry, which is a little less stable  as compared to octahedral or tetrahedral geometry.  As there are 5 substituents , this molecule is sp³d hybridized.Thus, in solid state , it splits into two ions as follows – 

[PCl₆] ^– ion has six substituents/ligands and so it has an octahedral geometry.

The central atom phosphorous is pentavalent i.e it has 5 valence electrons. In this ion it is attached to six chlorine atoms.This is possible as phosphorous atom can have an expanded octet i.e it has valence vacant d-orbitals where it can accommodate extra electrons from another chlorine atom.  One extra electron , which is accommodated in P atom’s d-orbital (which comes from another PCl₅ molecule)  gives this ion a negative charge.

[PCl₄] ⁺ ion has four substituents/ligands and so it has a tetrahedral geometry. It is sp³ hybridised.

Although phosphorous is pentavalent , in [PCl₄] ⁺ ion it is attached to only 4 substituents in this ion. The fifth valence electron is transferred to another PCl₅ molecule to form [PCl₆] ^– ion. As one electron is transferred to another species, the net charge on this ion is +1. 

The transfer can be shown as follows – 

Many compounds show this phenomenon.Some examples are –

1. PBr₅   →PBr₄⁺+ Br ^–…. Note that this molecule forms ions differently than PCl₅ as size of bromine atom is bigger than chlorine and so six bigger Br atoms do not sterically fit around P atom. 
2. PI₅   →PI₄⁺+ I ^–

3. Cl₂0₆ → Cl₂0₂⁺  + Cl₂0₄^–

In our next post we shall study another rule which is important in the hybridization series.Till then , 

Be a perpetual student of life and keep learning .. 

Good day !

References and Further Reading –

1. https://www.youtube.com/watch?v=6xBRMuqPoss