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

Q: Why does PCL5 exist 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 an 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, the NCl5 molecule cannot be formed.

So, the correct answer is B.

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

782.jpg

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

783.jpg

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.

784.jpg

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

785.jpg

Iodine is attached to six substituents and so according to VSEPR, it has octahedral geometry and sp3d2 hybridized. 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…

Good Day!

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