Valency And Ions

Radical or Ion :
When an atom looses or gains electrons it converts into Radical or Ion. (or) An atom or group of atoms with charge on them is called Radical or ion
(ii) Classification of ions: Ions can be classified as follows into two types of based on the type of atoms involved in ion formation.
(a) Simple ion : It is an ion which contains one or more atoms of the same element.
Ex : S^2-, O^2-etc,.
(b) Compound ion : It consists of  two or more atoms of different elements forming a single unit.
    Ex: \(S{O_4}^{2 - },N{O_3}^ - \), etc,.
Positive valency (Cation) : 
If the atom donates or looses its electrons from its outermost orbit to get stability, the valency is called as positive valency and the that ion is called as cation or Electropositive ion. (or) Radical or ion having positive charge on them is called Cation and shows positive valency. Cations are also called Basic Radicals.
Example: Na⁺, Ca²⁺, Al³⁺, 
Negative valency (Anion) : 
When an atom gain one or more electrons to get stability, The number of electrons  accepted by an atom of an element is its negative valency and the ion is called Anion or  Electronegative ion. (or)Radical or ion having negative charge on them is called anion.Anions are also called Acidic Radicals
Example: \(C{l^ - },\,{O^{2 - }},\,{N^{3 - }}\,,SO_4^{2 - },\,O_2^{2 - }\)
Discriptive Examples
i) Consider Sodium atom  (Na)
The atomic number of sodium (Na) is 11. 
Its electronic configuration is 2, 8, 1. 
The number of electrons present in outermost shell (Valence electrons) is 1.
Sodium looses 1 electron and attains the stable configuration of 2,8 i.e., Neon which is a noble gas element
So, valency of Sodium is taken as 1
Ion Formation
    After loosing one electron Sodium converts into Sodium ion. As it looses electron it converts to positive ion (generally called Cation).
\(\begin{gathered} \,\,\,\,\,Na\,\,\,\,\,\,\,\,\,\,\, \to \,\,\,\,\,\,\,N{a^ + }\,\, + \,\,1{e^ - } \hfill \\ 2,8,1\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,2,8 \hfill \\ \end{gathered} \)
ii) Consider Calcium atom (Ca)
The atomic number of Calcium (Ca) is 20. 
 Its electronic configuration is 2, 8, 8, 2. 
The number of electrons present in outermost shell (Valence electrons) is 2.
Calcium looses 2 electron and attains the stable configuration of 2,8,8 i.e., Argon which is a noble gas element
 So, valency of Calcium is taken as 2
Ion Formation
After loosing two electron Calcium converts into Calcium ion. 
\(\begin{gathered} \,\,\,\,\,\,\,\,Ca\,\,\,\,\,\,\,\,\,\,\, \to \,\,\,\,\,\,\,\,\,\,\,\,\,\,C{a^{2 + }}\,\, + \,2{e^ - } \hfill \\ 2,8,8,2\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,2,8,8 \hfill \\ \end{gathered} \)
iii) Consider Chlorine atom  (Cl)
The atomic number of Chlorine (Cl) is 17. 
Its electronic configuration is 2, 8, 7. 
The number of electrons present in outermost shell (Valence electrons) is 7.
Chlorine gaines 1 electron and attains the stable configuration of 2,8,8 i.e., Argon which is a noble gas element
So, valency of Chlorine is taken as 1
Ion Formation
After gaining one electron Chorine converts into Chloride ion. As it gains one electron it converts to negative ion (generally called Anion).
\(\begin{gathered} \,\,\,\,\,\,\,\,Cl\,\,\,\,\,\, + \,\,\,\,\,1{e^ - }\,\,\, \to \,\,\,\,\,\,\,\,\,\,C{l^ - }\,\, \hfill \\ 2,8,7\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,2,8,8 \hfill \\ \end{gathered} \)
Relation between valence electron and metallic and nonmetallic nature of Elements
(1) Elements having 1, 2 or 3 valency electrons are metals (except hydrogen).
    ₃Li (2, 1), ₁₁Na (2, 8, 1), ₁₉K (2, 8, 8, 1)   Valency electron 1 = Alkali metals
    ₁₂Mg (2, 8, 2), ₂₀Ca (2, 8, 8, 2)    Valency electrons are 2 = Alkaline earth metal
    ₁₃Al (2, 8, 3) Valency electrons are 3 = metal
(2) Elements having 5, 6, 7 valency electrons are nonmetals
    ₇N (2, 5), ₁₅P (2, 8, 5), ₃₃Sb (2, 8, 18, 5) Valency electrons are 5 = nonmetals
    ₈O (2, 6), ₁₆S (2, 8, 6), ₃₄Se (2, 8, 18, 6) Valency electrons are 6 = nonmetal
Halogens
    ₉F (2, 7), ₁₇Cl (2, 8, 7), ₃₅Br (2, 8, 18, 7), ₅₃lodine (2, 8, 18,18, 7) 
    Valency electrons are 7 = nonmetal
(3) Inert gases
    ₂He (2), ₁₀Ne (2, 8), ₁₈Ar (2, 8, 8) ₃₆Kr (2, 8, 18, 8), ₅₄Xe (2, 8, 18,18, 8)
    Valency electrons are 8 = non-metal