What is the difference between an atom and a molecule?

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An atom is the smallest constituent of matter that still retains the properties of a pure substance. Atoms make up elements. For example, iron metal is made up of iron atoms. A molecule, on the other hand, is made up of atoms of 2 or more different elements, combined in...

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An atom is the smallest constituent of matter that still retains the properties of a pure substance. Atoms make up elements. For example, iron metal is made up of iron atoms. A molecule, on the other hand, is made up of atoms of 2 or more different elements, combined in a certain fixed ratio. Atoms are single, pure forms of elements. Molecules are two or more atoms, and can be the same atom (H2, O2). Molecules can also be made of two or more different atoms, in which case they are also called a compound (H2O, CO2). Water is a molecule, made by combining 2 hydrogen atoms for every oxygen atom, thus ensuring a 2:1 ratio.

Molecules are made up of atoms joined together by bonding (ionic or covalent), whereas, in the case of an atom, the binding energy is more important and there is no bonding between the constituents of an atom (neutrons, protons and electrons).

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