Answer: d) [tex]Mg_2[/tex] is not stable
Explanation: Magnesium is an element with atomic number of 12, that is there are 12 electrons. So [tex]Mg_2[/tex] has 24 electrons which are arranged as follows according to molecular orbital theory.
[tex]Mg_2:\sigma1s^2\sigma^*1s^2\sigma2s^2\sigma^*2s^2\sigma2p_z^2 \pi2p_x^2=\pi2p_y^2\pi^*2p_x^2=\pi^*2p_y^2\sigma^*2p_z^2\sigma3s^2\sigma^*3s^2[/tex]
[tex]\text{bond order} =\frac{\text{no of bonding electrons - no of antibonding electrons}}{2}[/tex]
[tex]\text{bond order} =\frac{ 12-12}{2}[/tex]
[tex]\text{bond order}=0[/tex]
As the bond order is zero, that means there is no bond, thus [tex]Mg_2[/tex] is not stable and do not exist.
Mg2 does not exist because the molecule is unstable and has a bond order of zero.
The bond order of a molecule is obtained as half of the difference between the number of bonding and the antibonding electrons. Magnesium atom has 12 electrons so Mg2 molecule will have 24 electrons which are filled into molecular orbitals as follows;
σ1s2 σ*1s2 σ2s2 σ*2s2 σ2px2 π2py2 π2pz2 π*2py2 π*2pz2 σ*2px2 σ3s2 σ*3s2
The bond order in the molecule is; 1/2(12 - 12) = 0. A bond order of zero means that the molecule does not exist because it is unstable.
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