Ncert Exercises & Solutions

The species that does not have unpaired electrons is:

1.	\(N^+_2\)	2.	\(O_2\)
3.	\(O^{2-}_2\)	4.	\(B_2\)

HINT: MOT diagram will tell about unpaired electron.

Explanation:

Step 1:

Draw the MOT diagram of the given species and find the number of unpaired electrons.

The electronic configuration of the given molecules are :

1.)

N_{2}^{+}

= σ_{1 s^{2}},

σ_{1 s^{2}}^{*},

σ_{2 s^{2}},

σ_{2 s^{2}}^{*},

π_{2 {p_{x}}^{2}} \approx π_{2 {p_{y}}^{2}},

σ_{2 {p_{z}}^{1}}

It has one unpaired electron.

2.)

O_{2}

= σ_{1 s^{2}},

σ_{1 s^{2}}^{*},

σ_{2 s^{2}},

σ_{2 s^{2}}^{*},

σ_{2 {p_{z}}^{2}}, π_{2 {p_{x}}^{2}} \approx π_{2 {p_{y}}^{2}},

π_{2 {p_{x}}^{1}}^{*} \approx π_{2 {p_{y}}^{1}}^{*}

O_{2}

has two unpaired electrons.

3.)

O_{2}^{2 -}

= σ_{1 s^{2}},

σ_{1 s^{2}}^{*},

σ_{2 s^{2}},

σ_{2 s^{2}}^{*},

σ_{2 {p_{z}}^{2}}, π_{2 {p_{x}}^{2}} \approx π_{2 {p_{y}}^{2}},

π_{2 {p_{x}}^{2}}^{*} \approx π_{2 {p_{y}}^{2}}^{*}

Thus,

O_{2}^{2 -}

has no unpaired electrons.

4.)

B_{2}

= σ_{1 s^{2}},

σ_{1 s^{2}}^{*},

σ_{2 s^{2}},

σ_{2 s^{2}}^{*},

π_{2 {p_{x}}^{1}} \approx π_{2 {p_{y}}^{1}}

Thus,

B_{2}

has two unpaired electrons.

Step 2:

O_{2}^{2 -}

ion does not contain unpaired electrons.