Periodic Table and Valency of Elements

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a) Group IA, IIA and IIIA consists of metals of normal elements. They have 1, 2, or 3 valence electrons which they can easily donate to acquire the configuration of nearest noble gas. They become positively charged i.e., cations.

b) Group IVA, VA, VIA and VIIA consist of non-metals of normal elements. They have four, five, six and seven valence electrons. The elements of group VA, VIA and VIIA can accept 3, 2 or 1 electrons in their valence shell to attain the configuration of nearest noble gas. They become negatively charged i.e. Anions.

It is important to note the valency of an ion is always equal to charge on the ion.

For example: An ion with one positive charge such as Na¹⁺ has 1 electropositive valency. Similarly an ion with two positive charges such as Ca²⁺ has 2 electropositive valency. In the same way, ions having three or four positive charges on them will have 3 or 4 electropositive valency.

Similarly, those with one, two, three and four negative charges, will have monovalent, bivalent, trivalent and tetravalent electronegative valency.

Radical

A group of two or more different atoms having a net negative or positive charge such that it retains its identity in a series of chemical reactions is called a radical.

Example: SO₄^2-_, OH^1-_, NH₄¹⁺_.

List of common electropositive ions/radicals and electronegative ions/radicals.

01. Monovalent Cations (Cations having a valency of 1+)

i) Hydrogen ion, H⁺

ii) Lithium ion, Li⁺

iii) Sodium ion, Na⁺

iv) Potassium ion, K⁺

v) Ammonium ion, NH₄⁺

vi) Silver ion, Ag⁺

vii) Cuprous ion, Cu⁺

[Copper (I) ion]

viii) Mercurous ion, Hg⁺

[Mercury (I) ion]

02. Divalent Cations (Cations having a valency of 2+)

(i) Magnesium ion, Mg²⁺

(ii) Calcium ion Ca²⁺

(iii) Zinc ion Zn²⁺

(iv) Ferrous ion, Fe²⁺

[Iron (II) ion]

(v) Barium ion, Ba²⁺

(vi) Cupric ion, Cu²⁺

[Copper (II) ion]

(vii) Mercuric ion, Hg²⁺

[mercury (II) ion]

3. Trivalent Cations (Cations having a valency of 3+)

(i) Aluminium ion, Al³⁺

(ii) Chromium ion, Cr³⁺

(iii) Ferric ion, Fe³⁺

[Iron (III) ion]

4. Monovalent Anions (Anions having a valency of 1-)

(i) Fluoride ion, F^-

(ii) Chloride ion, Cl

(iii) Bromide ion, Br^-

(iv) Iodide ion, I^-

(v) Nitrite ion, NO2^-

(vi) Nitrate ion, NO3^-

(viii) Hydroxide ion, OH^-

(viii) Bicarbonate ion, HCO3^-

[Hydrogen carbonate ion]

(ix) Bisulphate ion, HSO4^-

[Hydrogen sulphate ion]

(x) Permanganate ion, MnO4^-

5. Divalent Anions (Anions having a valency of 2-)

(i) Oxide ion, O^2-

(ii) Sulphide ion, S^2-

(iii) Sulphite ion, SO₃^2-

(iv) Sulphate ion, SO₄^2-

(v) Carbonate ion, CO₃^2-

(vi) Chromate ion, CrO₄^2-

(vii) Dichromate ion, Cr₂O₇^2-

6. Trivalent Anions (Anions having a valency of 3-)

(i) Nitride ion, N^3-

(ii) Phosphide ion, P^3-

(iii) Phosphate ion, PO₄^3-

(iv) Borate ion, BO₃^3-