Question

Why does phosphorus show two valencies (3 and 5) ? Wouldn't it be easier to gain 3 electrons rather than losing 5 electrons? I mean if phosphorus loses five electrons, it'll have a 5+ charge, which is quite unstable, as explained in this video for carbon: https://youtu.be/4E8ShsaWssA .

Answer 1

Both the valencies of phosphorus (3 and 5) are due to sharing of electrons only. Phosphorus never loses or gains electrons as the condition given for carbon is applicable to phosphorus also. (Losing 5 electrons as well as gaining 3 electrons are difficult). Phosphorus is having 5 electrons in the valence shell. If it is written in orbital pattern (in higher level studies) it will be written as 2s2, 2p3. If phosphorus is using only electrons from p then the valence will be 3. If both the electrons from "s" as well as "p" are used the valence will be five. Both are due to sharing of electrons and both will form covalent compounds.