Question

please answer question 9 using the attached figure

%. Refer to Figure 5.17 in the textbook. Read the discussion on bonding in BH, in section 2.0. (a) Why does the 2p, atomic orbital become a non-bonding M.O. in BH, but is involved in bonding in NH? (consider what is required for an orbital on one atom to bond with an orbital on another atom or an LGO; consider the differences between the MO diagram for BH: in Fig 5.17 and that of NH3 in Fig 5.19)

Answer 1

No of the outer electron in the case of Boron is 3, whereas no of unpaired electron in the case of Nitrogen is 5. When Boron reacts with hydrogen and formed BH3 molecules then they first interact with each other and generate the new molecular orbital. The electrons are filled up in the molecular orbital according to the energy level of the molecular orbital. Because of the energy level and the different no of the unpaired electron, the 2pz atomic orbital became nonbonding for the BH3 and for bonding in the case of NH3.

In the case of BH3, the non-bonding orbital is vacant in the MO. But if we see the MO of NH3 then we found that the non-bonding orbital contains a lone pair of electron and which is higher in energy. Because of the difference in the nonbonding orbital BH3 acts as lewis acid whereas NH acts as a Lewis base.