Question

Which one is not stable and why?NF3, NF5, HNO3, NO, N2O5

Answer 1

Nf 5 is unstable because octet rule is not followed by nitrogen.

Answer 2

Answer: From the given molecules, the unstable molecule is $NF_5$

Explanation:

Nitrogen belongs to the Group 15 of the periodic table and its electronic configuration is $1s^22s^22p^3$ This element has 5 valence electrons.

To check the stability of the molecules, we first need to find out the hybridization of the molecules and it is calculated by using the Lewis dot structures of all the compounds.

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

Number of atomic orbitals around central metal atom = Number of bond pairs + Number of lone pairs

Bond pairs for a double bond and triple bond is taken as 1 only.

• Hybridization of nitrogen in $NF_3$

Number of bond pairs = 3

Number of lone pairs = 1

Number of atomic orbitals around Nitrogen atom = 3 + 1 = 4

So, hybridization will be $sp^3$

• Hybridization of nitrogen in $NF_5$

Number of bond pairs = 5

Number of lone pairs = 0

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

So, hybridization will be $sp^3d$. As, nitrogen does not have any d-orbitals, therefore this hybridization is not possible and hence, this compound is not possible. Therefore, it is an unstable molecule.

• Hybridization of nitrogen in $HNO_3$

Number of bond pairs = 3

Number of lone pairs = 0

Number of atomic orbitals around Nitrogen atom = 3 + 0 = 3

So, hybridization will be $sp^2$

• Hybridization of nitrogen in $NO$

Number of bond pairs = 1

Number of lone pairs = 0

Number of atomic orbitals around Nitrogen atom = 1 + 0 = 1

So, hybridization will be $sp$

• Hybridization of nitrogen in $N_2O_5$

Number of bond pairs = 3

Number of lone pairs = 0

Number of atomic orbitals around Nitrogen atom = 3 + 0 = 3

So, hybridization will be $sp^2$ and it will be same for both the nitrogen atoms.

Lewis dot structures of all the molecules are attached in the image below.

Thus, the unstable molecule is $NF_5$