78.CHEMICAL BONDING (25)- Covalent Bonding(24) – Problems(1).

Q: Why does PCl₅ exists but NCl₅ does not?
A. Ionization energy of N is very high
B.N does not have vacant d- orbitals
C.It does not have affinity for Cl
D. none of the above.

A: Nitrogen atom does not have vacant d – orbitals , and so it cannot have an expanded octet. So,NCl₅ molecule cannot be formed.

So, the correct answer is B.

Q:Explain  COCl₂ structure.
A: Phosgene (COCl₂) is poisonous gas. The structure of phosgene can be written as – 

Here the central carbon atom is sp² hybridised.  It forms three σ bonds with two chlorine and one oxygen atom and a π bond with oxygen atom.

Q:Predict the dot structure and geometry of iodine fluoride oxide (IOF₅).
A: Iodine and fluorine have 7 valence electrons and oxygen has 6 valence electrons.

∴Total no of valence electrons in IOF₅ molecule = 7 + 6 + 5(7) = 7 + 6 + 35 = 48 i.e 24 pairs of electrons.

If we arrange the atoms around iodine , and distribute the electrons we get the following structure – 

The bonds can be shown as follows – 

Iodine is attached to six substituents and so according to VSEPR it has octahedral geometry and sp³d² hybridised. Fluorine is more electronegative than oxygen.So, according to Bent’s rule oxygen should be at an equatorial position .However , oxygen is in the axial position.This is because the doubly bonded oxygen atom is more electronegative than fluorine. So, it occupies the axial position.

In the next post we shall try to solve more problems.Till then, 

Be a perpetual student of life and keep learning….

Happy Diwali !!