Question

8. Write the chemical formula: (i) Aluminium oxide (ii)Calcium
carbonate (ii) Magnesium hydroxide (iv) Sodium sulphide​

Answer 1

(1) Aluminium Chloride : AlCl

3

(4) Sodium sulfide : Na

2

S

(2) Magnesium Hydroxide : Mg(OH

Answer 2

(i) ALUMINUM OXIDE                     -  $Al_{2} O_{3}$

(ii) CALCIUM CARBONATE            -$CaCO_{3}$

(iii) MAGNESIUM HYDROXIDE      -$Mg(OH)_{2}$

(iv) SODIUM SULPHIDE                 -$Na_{2}S$

Explanation:

• The chemical formula of a compound is the symbolic representation of the elements which are undergoing bonding.
• While writing the chemical formula we use criss-cross method. In this method the valency of anion and cation are cross multiplied.
• The valency is the number of electrons gained or loosed by an atom to complete its octet.
• The valency of cations and anions are:

        Aluminum(Al)=+3

        Calcium(Ca)=+2

        Magnesium(Mg)=+2

        Sodium(Na)=+1

        Oxide(O)=-2

        Carbonate($CO_{3}$)=-2

        Hydroxide(OH)=-1

        Sulphide(S)=-2

• The chemical formulas will be: