Question

Helium and beryllium both have the same number of valence electrons. Then why is helium inert?

Answer 1

The electronic configuration of Helium is 2
The electronic configuration of Beryllium is 2,2
Helium is inert because it's outer electron orbit has 2 electrons, the maximum it can hold.
Beryllium has four electrons. The first two are in the inner orbit (same as He) and the other two are in the outer orbit that can hold eight electrons. Therefore, Be can either donate these two electrons, or accept 6 electrons from another element to achieve stable configuration. Hence it is not inert and will be reactive element due to which it is not stable like He.