Question

Phosphorus forms PCl5 but nitrogen doesnot form NCl5. why?

Answer 1

nitrogen has no free d-orbital in its valence cell elctron

Answer 2

Answer: Because nitrogen does not have d-orbital.

Explanation:

Nitrogen and phosphorous are the elements which belong to the same Group number which is 15 but to the different period number which are Period 2 and Period 3 respectively.

Electronic configuration of nitrogen atom: $1s^22s^22p^5$

Electronic configuration of phosphorous atom: $1s^22s^22p^63s^23p^5$

Phosphorus atom has d-orbital around it but nitrogen does not have.

To know the formation of compound of phosphorous pentachloride and nitrogen pentachloride, we need to find the stability around the central metal atom.

Formula used to calculate the number of atomic orbitals around central metal atom is:

• Hybridization of nitrogen in $NCl_5$

Number of bond pairs = 5

Number of lone pairs = 0

Number of atomic orbitals around Nitrogen atom = 5 + 0 = 5

So, hybridization will be $sp^3d$ . It is visible that the nitrogen atom does not have any d-orbitals, therefore this hybridization is not possible and hence, this compound is not possible. Thus, it is an unstable molecule.

• Hybridization of Phosphorous in $PCl_5$

Number of bond pairs = 5

Number of lone pairs = 0

Number of atomic orbitals around phosphorous atom = 5 + 0 = 5

So, hybridization will be $sp^3d$. It is visible that the phosphorous atom has d-orbitals, therefore this hybridization is possible and hence, this compound is possible. Thus, it is a stable molecule.

Therefore, Phosphorus forms $PCl_5$ but nitrogen does not form $NCl_5$.