Question
Use molecular orbital theory to explain why the Be2 molecule does not exist.
The molecular orbital electronic configuration for Be2 molecule can be written as:
$\sigma^2_\text{1s}\ \ \sigma^.2_\text{1s}\ \ \sigma^2_\text{2s}\ \ \sigma^.2_\text{2s}$
Hence, the bond order for Be2 is $\frac{1}{2}(\text{N}_\text{b}-\text{N}_\text{a}).$
Where
Nb = Number of electrons in bonding orbitals
Na = Number of electrons in anti-bonding orbitals
$\therefore$ Bond order of Be2 $= \frac{1}{2}(4-4)=0$
A negative or zero bond order means that the molecule is unstable. Hence, Be2 molecule does not exist.
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| | % Natural Abundance | Molar Mass |
| 35Cl | 75.77 | 34.9689 |
| 37Cl | 24.23 | 36.9659 |
$\text{CH}_3\text{CHCH}\equiv\text{CH}\\\ \ \ \ \ \ \ \ \ |\\ \ \ \ \ \ \ \ \ \text{CH}=\text{CH}_2$
$\Delta\text{H} = 400\text{kJ} \ \text{mol}^{–1} \text{and} \Delta\text{S} = 0.2\text{kJ} \ \text{K}^{–1} \ \text{mol}^{–1} $
At what temperature will the reaction become spontaneous considering $\Delta\text{H}$ and $\Delta\text{S}$ to be constant over the temperature range.