A compound is a chemical combination of two or more chemical elements in a fixed ratio.
When elements come together, they react with each other and form chemical bonds that are difficult to break. These bonds are formed as a result of sharing or exchanging electrons between atoms. The individual constituents of a compound do not retain their individual properties and they cannot be separated by physical means. Compounds are represented using a chemical formula.

Compounds can be classified based on the following:

• Nature
  • Organic compounds:
    An organic compound is defined as
    any compound whose molecules contain carbon and hydrogen(carbon-hydrogen bond). They
    are usually present in living matter.
    Examples are proteins, amino acids, ethanol, carbohydrates, etc
  
  
  • Inorganic compounds:
    These are compounds that do not possess carbon-hydrogen bonds. Examples are sulphuric acid, water, carbon dioxide, sodium chloride,etc


• Bonding
  • Ionic compounds
    These are compounds that are formed from the combination of metallic ions and non metallic ions. In this type of combination, there is transfer of electrons between the metal to the non-metal. Examples are sodium chloride, calcium carbonate, etc
  
  
  • Covalent compounds
    These are compounds that are formed by the sharing of electrons between non-metallic ions. Examples are chlorine gas, hydrogen chloride, Ammonia, etc