Page 87 - ICSE Chemistry 8

2–
• Oxygen (O) accepts 2 electrons to become oxygen ion (O ).
+2 electrons
2–
(8 electrons) O O (10 electrons)
Electronic confi gura on:
2–
0 2(K), 6(L) O 2(K), 8(L)
3–
• Nitrogen (N) accepts 3 electrons to become nitrogen ion (N ).
+3 electrons
3–
(7 electrons) N N (10 electrons)
Electronic confi gura on:
3–
N 2(K), 5(L) N 2(K), 8(L)
–
2–
Depending upon the number of electrons accepted, the elements are monovalent (Cl ), divalent (O ) or
3–
trivalent (N ).
Table 4.7: Valency and Symbol of Some Common Anions

Valency Symbol of ions Name

Monovalent Cl – Chloride
(1) Br – Bromide

I – Iodide
OH – Hydroxide
(NO ) – Nitrite
2
(NO ) – Nitrate
3
(HCO ) – Bicarbonate/Hydrogen carbonate
3
(HSO ) – Bisulphite/Hydrogen sulphite
3
(HSO ) – Bisulphate/Hydrogen sulphate
4
CH COO – Acetate
3
(MnO ) – Permanganate
4
Divalent O 2– Oxide
(2) S 2– Sulphide
(SO ) 2– Sulphite
3
(SO ) 2– Sulphate
4
(CO ) 2– Carbonate
3
(CrO ) 2– Chromate
4
(Cr O ) 2– Dichromate
2
7
(MnO ) 2– Manganate
4
Trivalent N 3– Nitride
(3) (PO ) 3– Phosphate
4

Variable Valency

Some elements show more than one valency. Such elements are said to have variable valency. For
example, copper, iron, silver, lead, n and mercury have variable valencies. Table 4.8 shows some metals
which have variable valencies.

73