WBJEE 2025 Physics and Chemistry Papers

To determine the bond order of HeH+, we can use the bond order formula:
Bond Order =‌

Nb−Na

2

where:
Nb is the number of electrons in bonding molecular orbitals.
Na is the number of electrons in antibonding molecular orbitals.
Here's how we can break it down:
Count the electrons:
Helium (He) normally has 2 electrons.
Hydrogen (H) has 1 electron.
Since the molecule is HeH+, one electron is removed from the total count.
Total electrons =2+1−1=2 electrons.
Form the molecular orbitals:
When the 1 s orbitals of He and H combine, they form a bonding orbital (σ1s) and an antibonding orbital (σ1s*).
With only 2 electrons available, both electrons will occupy the lower-energy bonding orbital ( σ1s), leaving the antibonding orbital empty.
Calculate the bond order:
Number of electrons in bonding orbitals, Nb=2.
Number of electrons in antibonding orbitals, Na=0.
Plugging into the formula:
Bond Order =‌

2−0

2

=1
Therefore, the bond order of HeH+is 1.
The correct answer is Option A: 1.