HOW TO WRITE CHEMICAL FORMULA ?

HOW TO WRITE CHEMICAL FORMULA ?

IT IS VERY EASY NOW.

CHEMICAL FORMULA:

It is the shorthand representation of name of a compound.

 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: