Question

What is the valency of phosphorus atoms in an excited state?

Answer 1

In excited state, electrons from an orbit having two electrons in valence shell are moved to the vacant orbit with lower energy. And valency of an atom is a tendency to make bonds with other atoms. Valency is also equal to the number of electrons shared by an atom in bonds formed by it.

Complete step by step answer:
We know that the atomic number of phosphorus is 15 and its electronic configuration in ground state is $\left[ {Ne} \right]3{s^2}3{p^3}$. We know that phosphorus also has a vacant 3d-orbital.
In an excited state, electrons are excited from lower energy level to higher energy level. Here in phosphorus in an excited state an electron is excited from 3s to 3d orbit. Now, the electronic configuration of phosphorus in excited state is $\left[ {Ne} \right]3{s^1}3{p^3}3{d^1}$.
In the electronic configuration of the excited state of phosphorus, we can see that there are five unpaired electrons in it.
Valency of an atom is its tendency to make bonds with other atoms. Here in an excited state phosphorus has five unpaired electrons means it can form five bonds with some other atoms.
Then the valency of phosphorus in excited state is 5 and the correct answer is option C.

Note: Phosphorus belongs to the nitrogen family and it can form five bonds or its valency is five in an excited state. But nitrogen forms maximum four bonds that are in $N{H_4}^ +$. This is because nitrogen belongs to the second period and it does not have vacant d-orbital in its valence shell.