Question 1 Page 39 - Chapter 3 Class 9 - Atoms And Molecules

Write down the formulae of (i) Sodium Oxide (ii) Aluminium Chloride (iii) Sodium Sulphide (iv) Magnesium Hydroxide

Answer

(i) Sodium Oxide

It contains 2 elements Sodium(Na) and Oxygen(O)

• Valency of Sodium (Na) is 1

• Valency of Oxygen (O) is 2

These valencies interchange while writing formula as shown below

(ii) Aluminium Chloride 

It contains 2 elements Aluminium(Al) and Chlorine(Cl)

• Valency of Aluminum (Al) is 3

• Valency of Chlorine (Cl) is 1

These valencies interchange while writing formula as shown below

Hence, the formula becomes AlCl ₃

(iii) Sodium Sulphide

It contains 2 elements Sodium(Na) and Sulphur(S) 

Valency of Sodium (Na) is 1

Valency of Sulphur (S) is 2

These valencies interchange while writing formula as shown below

Hence, the formula becomes Na ₂ S

(iv) Magnesium Hydroxide

It contains 2 elements Magnesium(Mg) and Hydroxide(OH)

Valency of Magnesium (Mg) is 2

Valency of Hydroxide (OH) is 1

These valencies interchange while writing formula as shown below

Hence, the formula becomes Mg(OH) ₂