Two or more elements combine together chemically to form a new substance called compound. Compounds are commonly termed as chemical compounds, bed these are formed due to a chemical reaction between two or more elements. Thus, a compound is pure substance made up of two or more elements combined chemically in a definite proportion by mass (or by weight).
For example, water is a chemical compound made up of hydrogen and oxygen combined in the ratio 2:1by volume, or 1:8 by mass.
Characteristics of a chemical compound
A chemical compound has the following characteristics:
(i) A chemical compound is obtained by the chemical combination of two or more elements in a definite proportion by mass.
(ii) Compounds are homogeneous, i.e. their properties are the same throughout.
(iii) The chemical and physical properties of a compound are entirely different from those of the constituent elements. For example, hydrogen is a combustible gas, while oxygen is a supporter of combustion, but their compound, water is neither combustible nor a supporter of combustion.
(iv) During the formation of a compound from its elements, a certain amount of energy in the form of heat, light, electricity is either absorbed or evolved. For example, when carbon burns, it reacts with oxygen to form carbon dioxide is a chemical compound, and its formation from the elements involve the evolution of heat.