Is there any relationship between the valency of an element and the number of electrons its atom has in its outermost shell?
Before knowing the relation let's take a quick peek into their definitions
Valency
It is the combining capacity of an element with the atoms of another element to form a chemical compound.
And who combines?
They are the electrons.
Valence Electrons
These are the electrons that combine with other atoms to form a chemical compound.These electrons are the ones that are present in outermost shell of an element , and they only take part in forming new compounds not all the electrons.
So, the valency of an element is the number of valence electrons lost,gained or shared when forming a compound.An atom loses,gains or shares electrons so as to achieve the noble gas configuration.
For, example Na (sodium) , Cl (Chlorine)
Na has the electronic configuration --> 2,8,1
It has once valence electron, so this 1 electron takes part in reactions,hence this the valency of Na (+1).
Cl has the electronic configuration --> 2,8,7
It has 7 valence electrons, but it can't lose so many because it would involve a lot of energy, so it gains an electron.So, its valency is - 1.
Predict the valencies of helium (He), phosphorus (P), sulphur (S) and neon (Ne). The atomic numbers of these elements are, 2, 15, 16 and 10, respectively.
helium = 0
phosphorus = 3
sulphur = 2
neon = 0
