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Chemistry Question on Chemical bonding and molecular structure

Amongst the following, the total number of species NOT having eight electrons around central atom in its outer most shell, is NH3, AICI3, BeCl2, CCl4, PCI5 :

A

2

B

4

C

1

D

3

Answer

3

Explanation

Solution

Let's analyze each species:

NH 3 (Ammonia): Nitrogen (N) has 5 valence electrons. In NH3, there are three shared electron pairs around nitrogen (one from each hydrogen atom). The total number of electrons around the central nitrogen atom is 3 x 2 (shared pairs) + 2 (non-bonding pair) = 8. So, NH3 has eight electrons around the central atom.
AlCl 3 (Aluminum trichloride): Aluminum (Al) has 3 valence electrons, and chlorine (Cl) has 7 valence electrons each. In AlCl3, aluminum forms three bonds with chlorine, and each chlorine atom has 3 lone pairs. The total number of electrons around the central aluminum atom is 3 x 2 (shared pairs) + 6 (non-bonding pairs) = 12. So, AlCl3 does not have eight electrons around the central atom.
BeCl 2 (Beryllium dichloride): Beryllium (Be) has 2 valence electrons, and chlorine (Cl) has 7 valence electrons each. In BeCl2, beryllium forms two bonds with chlorine, and each chlorine atom has 3 lone pairs. The total number of electrons around the central beryllium atom is 2 x 2 (shared pairs) + 6 (non-bonding pairs) = 10. So, BeCl2 does not have eight electrons around the central atom.
CCl 4 (Carbon tetrachloride): Carbon (C) has 4 valence electrons, and chlorine (Cl) has 7 valence electrons each. In CCl4, carbon forms four bonds with chlorine. The total number of electrons around the central carbon atom is 4 x 2 (shared pairs) = 8. So, CCl4 has eight electrons around the central atom.
**PCl 5 (Phosphorus pentachloride): **Phosphorus (P) has 5 valence electrons, and chlorine (Cl) has 7 valence electrons each. In PCl5, phosphorus forms five bonds with chlorine. The total number of electrons around the central phosphorus atom is 5 x 2 (shared pairs) = 10. So, PCl5 does not have eight electrons around the central atom.

Now, let's count the species that do not have eight electrons around the central atom:

AlCl3, BeCl2, PCl5 (3 species)

The correct answer is (D): 3.