Chemical Formula - Class 7 PDF Download

Chemical Formula

As already stated, a chemical formula is a symbolic expression signifying the number of atoms present in a molecular substance. We determine the type of atom by referring to its symbol, so for Hydrogen, we will use H. The number of atoms is determined by the subscript attached to the symbol.  So a chemical formula of water, i.e H₂O has two atoms of hydrogen and a single atom of oxygen.

Steps to write a chemical formula

Step 1: First, you have to decide the type of the bond.

If the prefixes are used, then it is a covalent bond. In case there are no prefixes, it is an ionic bond. After that is decided move to Step number 2.

Step 2: Now, write down the symbol of the polyatomic ion or the element.

Step 3: Now, if the prefix was used, you’ll have to add a subscript. You’ll also have to add a subscript in order to balance the charge.

Solved Example For You

Q. Write the chemical formulae for

1. Hexane
2. Sodium Chloride

Ans. C₆H₁₄ – this has 6 atoms of carbon and 14 atoms of Hydrogen and is collectively called Hexane. NaCl- also known as Sodium Chloride or common salt, this formula has a single atom of Sodium and a single atom of Chloride. Always remember that in places where there is no subscript, like in the example above, the value of atom is presumed to be 1.