In chemistry, an element is a pure substance which cannot be broken down by chemical means, consisting of atoms which have identical numbers of protons in their atomic nuclei. The number of protons in the nucleus is the defining property of an element, and is referred to as the atomic number. Example of and element would be Mercury.
A chemical compound is a chemical substance composed of many identical molecules composed of atoms from more than one element held together by chemical bonds. Two atoms of the same element bonded in a molecule do not form a chemical compound, since this would require two different elements. Example of a compound would be acids such as NITRIC HNO3)
A molecule is the smallest unit of a substance that has all the properties of that substance. For instance, a. water molecule is the smallest unit that is still water. A water molecule can be divided into tiny parts called atoms. This produces two hydrogen atoms and one oxygen atom.