Chemistry - CHEMICAL BONDING Question with Solution | TestHub

The existence of a species is determined by its bond order. A species exists if its bond order is greater than zero.

1. For ${\mathrm{He}}_2^{+2}$: Total electrons = $2+2-2=2$. Configuration: $(\sigma 1s{)}^2$. Bond order = $\frac{1}{2}(2-0)=1$. Exists.

2. For ${\mathrm{He}}_2$: Total electrons = $2+2=4$. Configuration: $(\sigma 1s{)}^2({\sigma }^{\ast }1s{)}^2$. Bond order = $\frac{1}{2}(2-2)=0$. Does not exist.

3. For ${\mathrm{He}}_2^{+}$: Total electrons = $2+2-1=3$. Configuration: $(\sigma 1s{)}^2({\sigma }^{\ast }1s{)}^1$. Bond order = $\frac{1}{2}(2-1)=0.5$. Exists.

Therefore, ${\mathrm{He}}_2$ does not exist.

The final answer is $\boxed{H{e}_2}$.