Question

MO configuration of He₂⁻ is
(a) (σ 1s)², (σ* 1s)², (σ 2s)¹ (b) (σ 1s)², (σ* 1s)², (σ* 2s)¹
(c) (σ 1s)², (σ* 1s)¹, (σ 2s)² (d) (σ 1s)², (σ* 1s)¹, (σ* 2s)²

Answer 1

MO configuration of He₂⁻ is (σ 1s)², (σ* 1s)², (σ 2s)¹

Explanation:

$He_2^{-}$ ion is formed by 1 $He$ atom and 1 $He^{-}$ ion.

Atomic number of $He$ is 2. Hence number of electrons in $He$ atom =2

And number of electrons in $He^{-}$ ion = 2+1=3

Therefore, total number of electrons in $He_2^{-}$ ion = 2+3 =5

According to MOT, MO configuration of $He_2^{-}$ ion is $\sigma1s^2,\sigma^*1s^2,\sigma2s^1$

Therefore, the correct answer is option (a)

Answer 2

MO configuration of He₂⁻ is (σ 1s)², (σ* 1s)², (σ 2s)¹

He_2^{-}He

2

−

ion is formed by 1 HeHe atom and 1 He^{-}He

−

ion.

Atomic number of HeHe is 2. Hence number of electrons in HeHe atom =2

And number of electrons in He^{-}He

−

ion = 2+1=3

Therefore, total number of electrons in He_2^{-}He

2

−

ion = 2+3 =5

According to MOT, MO configuration of He_2^{-}He

2

−

ion is \sigma1s^2,\sigma^*1s^2,\sigma2s^1σ1s

2

,σ

∗

1s

2

,σ2s

1

Therefore, the correct answer is option (a)