`=>` We have seen that `1s` atomic orbitals on two atoms form two molecular orbitals designated as `σ1s` and `σ^(ast)1s`.
● In the same manner, the 2s and 2p atomic orbitals (eight atomic orbitals on two atoms) give rise to the following eight molecular orbitals :
`tt ( ( text{Antibonding} , MOs , σ^(ast)2s , σ^(ast)2p_z , π^(ast)2p_x , π^(ast)2p_y ) , ( text{Bonding} , MOs , σ2s , σ2p_z , π2p_x , π2p_y ))`
`=>` The energy levels of these molecular orbitals have been determined experimentally from spectroscopic data for homonuclear diatomic molecules of second row elements of the periodic table.
● The increasing order of energies of various molecular orbitals for `O_2` and `F_2` is given below :
`σ1s < σ^(ast)1s < σ2s < σ^(ast)2s < σ2p_z < (π 2p_x = π 2p_y) < (π^(ast)2p_x= π^(ast)2p_y) < σ^(ast)2p_z`
`=>` But, this sequence of energy levels of molecular orbitals is not correct for the remaining molecules `Li_2`, `Be_2`, `B_2`, `C_2`, `N_2`.
`=>` For instance, it has been observed experimentally that for molecules such as `B_2`, `C_2`, `N_2` etc. the increasing order of energies of various molecular orbitals is
`σ1s < σ^(ast)1s < σ2s < σ^(ast)2s < (π 2p_x = π 2p_y) < σ2p_z < (π^(ast)2p_x= π^(ast)2p_y) < σ^(ast)2p_z`
`=>` The important characteristic feature of this order is that the energy of `σ2p_z` molecular orbital is higher than that of `π 2p_x` and `π 2p_y` molecular orbitals.
`=>` We have seen that `1s` atomic orbitals on two atoms form two molecular orbitals designated as `σ1s` and `σ^(ast)1s`.
● In the same manner, the 2s and 2p atomic orbitals (eight atomic orbitals on two atoms) give rise to the following eight molecular orbitals :
`tt ( ( text{Antibonding} , MOs , σ^(ast)2s , σ^(ast)2p_z , π^(ast)2p_x , π^(ast)2p_y ) , ( text{Bonding} , MOs , σ2s , σ2p_z , π2p_x , π2p_y ))`
`=>` The energy levels of these molecular orbitals have been determined experimentally from spectroscopic data for homonuclear diatomic molecules of second row elements of the periodic table.
● The increasing order of energies of various molecular orbitals for `O_2` and `F_2` is given below :
`σ1s < σ^(ast)1s < σ2s < σ^(ast)2s < σ2p_z < (π 2p_x = π 2p_y) < (π^(ast)2p_x= π^(ast)2p_y) < σ^(ast)2p_z`
`=>` But, this sequence of energy levels of molecular orbitals is not correct for the remaining molecules `Li_2`, `Be_2`, `B_2`, `C_2`, `N_2`.
`=>` For instance, it has been observed experimentally that for molecules such as `B_2`, `C_2`, `N_2` etc. the increasing order of energies of various molecular orbitals is
`σ1s < σ^(ast)1s < σ2s < σ^(ast)2s < (π 2p_x = π 2p_y) < σ2p_z < (π^(ast)2p_x= π^(ast)2p_y) < σ^(ast)2p_z`
`=>` The important characteristic feature of this order is that the energy of `σ2p_z` molecular orbital is higher than that of `π 2p_x` and `π 2p_y` molecular orbitals.