Compounds are pure substances formed by the chemical combination of two or more elements in a definite proportion by mass.
The four Important characteristics of compounds are:
1. A compound is made up of one or more atoms of the same or different elements.
2. A compound has properties entirely different from the properties of its constituents.
3. Components of a compound are present in a definite proportion.
4. The components cannot be separated into its constituents by simple physical means.