Question

Which one of the following species is not likely to exist? $H_{2}^{+}$, HeH, $He_{2}$.

Answer 1

$\sf{He_2}$ doesn't exist. This is because He ( Helium ) is a noble gas and it's octet is fully complete. So, He doesn't react with anyone.

Answer 2

Answer:

For H

2

−

, 1s

2

∗1s

1

Bond Order =

2

2−1

=0.5

For He

2

−2

, 1s

2

∗1s

2

2s

2

Bond Order =

2

4−2

=1

For He

2

, 1s

2

∗1s

2

Bond Order =

2

2−2

=0

For H

2

+2

, 1s

0

Bond Order =

2

0−0

=0

For H

2

−

, 1s

2

∗1s

1

Bond Order =

2

2−1

=0.5

For He

2

+2

, 1s

2

Bond Order =

2

2−0

=1

For H

2

+

, 1s

1

Bond Order =

2

1−0

=0.5

The bond order of H

2

2+

and He

2

is zero, thus their existence is not possible.

Hence, option B is correct.