Question

Use Molecular Orbital Theory to describe bonding in the following. Also find the bond order and decide if stable or not. Is species dia or paramagnetic?

i. C₂⁺   ii. Be₂⁺   iii. Ne₂

Answer 1

1) C₂⁺ ---> total electrons = 11

sigma 1s² < sigma* 1s² < sigma 2s² < sigma* 2s² < (pi 2p_x² = pi 2p_y¹)

Bond order = (1/2)*[number of electrons in bonding orbitals - number of electrons in non-bonding orbitals]

or, Bond order = (1/2)*[7 - 4] = 1.5

Sice, there is one unpaired electron in the orbital pi 2p_y , hence the substance is paramagnetic

Since, Bond Order > 0 , hence stable

2) Be₂⁺ ----> total electrons = 7

sigma 1s² < sigma* 1s² < sigma 2s² < sigma* 2s¹

Bond order = (1/2)*[number of electrons in bonding orbitals - number of electrons in non-bonding orbitals]

or, Bond order = (1/2)*[4 - 3] = 0.5

Since, there is one unpaired electron in the orbital in sigma* 2s, hence the substance is paramagnetic

Since, Bond order > 0 , hence stable

3) Ne₂ -----------> Total electrons = 20

sigma 1s² < sigma* 1s² < sigma 2s² < sigma* 2s² < (pi 2p_x² = pi 2p_y²) < sigma 2p_z² < (pi* 2p_x² = pi* 2p_y²) < sigma* 2p_z²

Bond order = (1/2)*[number of electrons in bonding orbitals - number of electrons in non-bonding orbitals]

or, Bond order = (1/2)*[10 - 10] = 0

Sice, there is no unpaired electron , hence the substance is diamagnetic

Since Bond order = 0, hence the substance is unstable