Question

BeH2 is an odd compound for two reasons: even though it is made up of a metal and a nonmetal, it bonds covalently, and it violates the octet rule. Briefly explain how both of these oddities happen in BeH2. In this explanation, make sure to address electronegativity and the octet rule.

Answer 1

In BeH₂ molecule, the ₄Be atom is sp hybridised involving 2s and 2px atomic orbitals during hybridisation. There is one lone pair of electrons on Be. The sp hybridised Be orbitals will overlap with the s-orbital of H-atom giving a linear geometry to the molecule. It is an electron deficient molecule.

Ground state electronic configuration of Be is 1s² 2s²

Excited state electronic configuration of Be is 1s² 2s¹2p_x¹

Hybridised state Be is 1s² (sp)¹(sp)¹

@ BH (н. - Be - H)

In the Lewis dot structure, Be has 6 electrons around it, which is electron deficient molecule according to Lewis octet rule.

The octet rule refers to the tendency of atoms to prefer to have eight electrons in the valence shell. When atoms have fewer than eight electrons, they tend to react and form more stable compounds. Thus, an atom continues to form bonds until an octet of electrons is made. This is known as octet rule by Lewis.

BeH₂ is covalent hydride. Berylium has a rather high positive charge on it, and it is a fairly small cation, so according to Fajans' rules, we could predict it to be covalent.

Electronegativity of be on Pauling's scale is 1.57 and that of H is 2.1. The electronegativity difference between Be and H is 0.53 indicates partially ionic and partially covalent.It is a non-polar molecule, from dipole moment measurements.