Reason for ion formation –

Atoms either loose or gain electrons to achieve stable octet

Atoms with 1/2/3 electrons easily loose these to gain stability since the inner shell is filled and has an octet of electrons.

Atoms which contain 5/6/7 electrons in outermost shell easily gain 3/2/1 electron to complete the octet.

H (1) has 1 e in its outermost shell which is easily lost to form H⁺

Li (2,1) has 1 e in its outermost shell which is easily lost to form Li⁺

Be (2,2) has 2 electrons in outermost shell which are easily lost to form Be ⁺²

B (2,3) has 3 electrons in outermost shell which are easily lost to form B ⁺³

C (2,4)  has 4 electrons in outermost shell which are easily lost to form C ⁺⁴

N (2,5) has 5 electrons in outermost shell hence easily gains 3 more electrons to form N^-3

O ( 2,6)  has 6 electrons in outermost shell hence easily gains 2 more electrons to form O ^-2

F ( 2,7)  has 7 electrons in outermost shell hence easily gains 1 more electron to form F ^–

Na ( 2,8,1) has 1 electron in outermost shell which is easily lost to for Na ⁺

Mg ( 2,8,2) has 2 electrons in outermost shell which are easily lost to form Mg ⁺²

Al ( 2,8,3)  has 3 electrons in outermost shell which are easily lost to form Al ⁺³

Si ( 2,8,4)  has 4 electrons in outermost shell which are easily lost to form Si ⁺⁴

P ( 2,8,5)  has 5 electrons in outermost shell hence easily gains 3 more electrons to form P ^-3

S ( 2,8,6)  has 6 electrons in outermost shell hence easily gains 2 more electrons to form S ^-2

Cl ( 2,8,7)  has 7 electrons in outermost shell hence easily gains 1 more electron to form Cl ^–

K ( 2,8,8,1)  has 1 electrons in outermost shell which is easily lost to form K ⁺

Ca ( 2,8,8,2)  has 2 electrons in outermost shell which are easily lost to form to form Ca ⁺²