Question

Both helium(He) and beryllium (Be) have two valence electrons. But helium is inert gas and zero valent whereas beryllium shows a valency of 2.

Answer 1

• The electronic configuration of Helium and Beryllium are as follows:
• He : K =2 Be : K=2, L=2.
• In the He atom, the two electrons are present in the K shell whose maximum capacity is 2 electrons. Therefore, the shell is completely filled. As a result, the shows no chemical activity and is, therefore, zero valency.
• In Be atom the outermost shell or the valence shell is the L shell. the It also has two electrons but it is partly filled because the maximum capacity of L shell is 8 electrons. As these two valence electrons take part in the bond formation. Therefore, the valency is Be is 2.