NCERT Question 4 - Chapter 3 Class 9 - Atoms And Molecules

Write the chemical formulae of the following.

(a) Magnesium Chloride

(b) Calcium Oxide

(c) Copper Nitrate

(d) Aluminium Chloride

(e) Calcium Carbonate.

Answer

(a) Magnesium Chloride

It contains 2 elements Magnesium(Mg) and Chlorine(Cl)

Valency of Magnesium (Mg) is 2

Valency of Chlorine (Cl) is 1

These valencies interchange while writing formula as shown below

Hence, the formula becomes MgCl ₂

(b) Calcium Oxide

It contains 2 elements Calcium(Ca) and Oxygen(O)

Valency of Calcium (Ca) is 2

Valency of Oxygen (O) is 2

These valencies interchange while writing formula as shown below

Hence, the formula becomes CaO

(c) Copper Nitrate

It contains 2 elements Copper(Cu) and Nitrate(NO 3 )

Valency of Copper(Cu) is 2

Valency of Nitrate(NO ₃ ) is 1

These valencies interchange while writing formula as shown below

Hence, the formula becomes Cu(NO ₃ ) ₂

(d) 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

(e) Calcium Carbonate

It contains 2 elements Calcium(Ca) and Carbonate(CO 3 )

Valency of Calcium (Ca) is 2

Valency of Chlorine (CO ₃ ) is 2

These valencies interchange while writing formula as shown below

Hence, the formula becomes CaCO ₃