When two or more elements combine to form a new substance, it is called a compound. ... The smallest part of a compound is a molecule. A compound is made when atoms of two or more elements bond in a chemical reaction. Two hydrogen atoms and one oxygen atom bond to form a molecule of water (H2O).
Elements can be chemically combined into compounds, therefore, a compound consists of two or more elements combined, in definite proportions, by chemical means. Compounds may be formed by combining atoms of their constituent elements by ionic bonds or by covalent bonds.
