Molecule vs. Atom

Difference Between Molecule and Atom

Matter is made up of atoms and molecules. So, they are the building blocks of all things in the world. Even we are made up of atoms and molecules. In simple terms, the basic and the smallest unit of any element is atom. An atom exhibits all the properties of that element. For instance, the smallest unit of oxygen gas is the atom of oxygen represented as O. This atom of oxygen does not exist independently.  It combines chemically with another atom of oxygen so as to become stable forming a molecule represented by O2.

Molecules of a substance may not necessarily be made up of the same atoms. Most common example of the molecule is the molecule of water which is made up of 2 atoms of Hydrogen and one atom of Oxygen represented as H2O.


The smallest particle of an element which cannot exist freely of its own, and take part in a chemical reaction is called. An atom cannot be observed with a naked eye. Electron microscope magnifies an atom up to 200,000 times to make it for us to see.  Atoms are made up of sub atomic particles named electrons, protons, and neutrons. Protons have positive charge and electrons have negative charge. There is no charge in neutrons. Protons and neutrons exist inside a nucleus. Electrons revolve around the nucleus in orbits. Each orbit of electrons has certain level of energy. Every atom has the same number of electrons and protons. Therefore atoms are electrically neutral. Atoms of most elements except the inert gases are unstable. Therefore, their outermost shell is consisted of less than 8 electrons. The outermost shell of an atom of metallic elements is consisted of 1, 2, 3 electrons.  In the non-metallic elements 5, 6, 7 valence electrons are present in the outer shell.


The smallest particle of an element that exists independently is called molecule. An electrostatic force holds the Molecules together. The total of the mass of all the atoms present in a molecule is called molecular mass. Molecules exhibit a definite set of properties. They are stable in nature. Molecule takes part in a chemical reaction. 2 atoms of oxygen are combined together to form one molecule of oxygen. It then becomes the gas. But 3 atoms of oxygen also combined together form one molecule of ozone gas.

Above analysis shows that atoms and molecules are found in all non- living things and living things in the universe. The arrangement of atoms and molecules determines the physical and chemical properties of a substance. For example, molecules in liquid are slightly compact while in gases they are loosely held together. In solid they are very compact.


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