CHEMICAL FORMULA

CHEMICAL FORMULA

The shorthand representation of compound. name of a

Eg:Sodium chloride-Nacl

Eg:Sodium hydroxide-NaOH

Eg:Sodium Carbonate- Na₂CO₃ etc.

Ionic Compounds:

The compounds which are having ions in them. (Or)

The compounds which are made up of ions

Eg: sodium chloride - sodium and chloride ions in it.

Eg:Calcium carbonate - calcium and Carbonate ions in it.

To write chemical formula of ionic compound,we use "Criss-Cross method" (or) " ionic formula method".

Criss-Cross Method:

It is used to compounds. write chemical formulae of ionic compounds.

Rules:-

1) Write down the cation symbol/formula at L.H.S,& Anion symbol/formula of at R.H.S.

2) Remove the Sign (+/-) from the charge on it. (& The remaining numbers are called as valencies).

3) Cancel the valencies if possible,

4) Now criss-cross the valencies 

Cation valency given to Anion.

Anion Valenicy given to Cation.

5)Write down the numbers at R.H.S bottom to the symbols or formulae after criss-crossing the valencies.

6) Use bracket for compound ions which are getting more than I number (after criss Cross).

7) Don't mention 1 number for simple & compound ions(do not use bracket)

8) Do not disturb the formula of cation & Anion (Except sign or +/- charges ).

9.Do not mention.1 number in chemical formula.

Examples: