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.


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[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 PClas 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. Cl20→ 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

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