Class 9 Chemistry Atoms and Molecules Writing chemical formula

Writing chemical formula

  • RULE I: Cross multiply the valencies of the elements to form the formula of the respective compound.

In the above formulas Rule I is followed i.e. cross multiply the valencies of the elements to form the formula of the respective compound.

 

  • RULE II: If a compound consists of both metallic as well non-metallic elements then name or symbol of the metal is considered first.

Where Mg (magnesium) is a metal and Cl (chlorine) is a non-metal.

  • RULE III: In case compounds are formed from polyatomic ions then the ion is enclosed in a bracket before writing the number to indicate the ratio. But in case the number of polyatomic ion is one then there is no need for bracket.

Since the number of polyatomic ion is one therefore no brackets are required.

The formula for calcium hydroxide is Ca(OH)2. The brackets around oh with subscript 2 implies the presence of two hydroxyl group joined to one calcium atom.

 

Share these Notes with your friends  

< Prev Next >

You can check our 5-step learning process


.