Page 104 - ICSE Chemistry 8

Example 2: A molecule of carbon dioxide is formed by combining the atoms of elements carbon and
oxygen.
Carbon: C Oxygen: O

C O
4 –2

C O 4
2
Simplify the formula by dividing the valencies by common factor 2.
CO 2

Therefore, the chemical formula of carbon dioxide is CO .
2
Example 3: Sodium chloride is formed by combining the atoms of elements sodium and chlorine.

Sodium: Na Chlorine: Cl
Na Cl

1 –1

NaCl is the chemical formula.

Example 4: Calcium hydroxide is formed by combining calcium and hydroxide (a radical).

Calcium: Ca Hydroxide: OH
Ca OH

2 –1

Ca(OH) is the chemical formula.
2
Example 5: Sodium carbonate is formed by combining sodium and carbonate (a radical).

Sodium: Na Carbonate: CO 3
Na CO 3

1 –2

Na CO is the chemical formula.
2
3
Significance of a Chemical Formula

The chemical formula of a compound indicates the following informa on.

• The name of the compound.
• The names of the cons tuent elements.

• The number of atoms of various elements or ions present in one molecule of the compound.

Table 5.8 shows us the chemical or molecular formulae of some common compounds.

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