What is special about valence electrons?

the valence electron(s) are the one(s) which an atom gains
or loses or shares during the chemical reaction.

An element
gains or loses electrons according to:1- being metal so it loses electrons (like the
sodium atom which has 1 electron in the outer shell , magnesium atom which has 2
electrons in the outer shell) 2- being non-metal so it gains electrons (like flourine
atom which has 7 electrons in the outer shell , nitrogen which has 5 electrons in the
outer shell) 3- being inert gas (but these type of atoms don't share in chemical
reactions under ordinary conditions)

Metals always tend to
lose their valency electron(s) and these electrons in the outer level (shell)  vary from
: 1 to 3 electrons so it's easier for the matals to lose them because gaining 5,6 or 7
electrons  will be harder .

Non-metals always tend to gain
or share electrons ,,,,, gain electrons in ionic bonds : NaCl where sodium loses an
electron and gives it to a chlorine atom so Cl puts in its  outer level. The
non-metals share electrons in covalent bonds which arises between 2 non-metals : like :
nitrogen + nitrogen= nitrogen molecule  where each nitrogen atom shares by 3 electrons
with the other nitrogen and they form one nitrogen molecule together
 ,,,,,

Why do elements share, lose or gain their valency
electrons? in order to be in a stabled state and each atom has 8 electrons in its outer
level and that's why the inert gases don't enter chemical reactions since they already
have outer levels completely filled with electrons.