Difference between Atom and Molecule

Atom vs. Molecule

What is difference between atom and molecule? The concepts “atom” and “molecule” are part of the terminology that must be mastered when an introduction to Chemistry is made and for this very reason it is important that we know the differences between atom and molecule.

Difference between Atom and Molecule


On the one hand, atoms are part of the constituents of matter and range from 0.1 to 0.5 nanometers wide. They are so small that they cannot even be seen through a common microscope. There are many types of atoms and each has a unique number, mass and size. Clusters of atoms of the same type constitute the chemical elements.

An element is a pure chemical substance that has atoms of the same class and is distinguished by its atomic number. The atomic number derives from the quantity of protons present in the nucleus of the atoms of the element.

To date, 118 elements have been discovered and have been divided into: metals, metalloids and nonmetals. Each element has its own set of properties and most are found on earth; while a few have developed from nuclear reactions . All elements can be found in the periodic table, listed according to their atomic number.

The atoms of each element are composed of protons, neutrons and electrons. Protons and neutrons are found in the nucleus, located in the center of atoms. While the electrons that spin around, they are attached to the nucleus thanks to the electromagnetic force. The electrons have a negative electric charge and this is why they are attracted to the nucleus, since the protons have a positive electric charge. On the other hand, the neutrons have no electric charge.

The atoms of different elements unite and form molecules. This happens through chemical reactions. For example: two atoms of hydrogen and one of oxygen, combine to make a molecule of water.


A molecule is the smallest amount that can exist of a substance. It is constituted by atoms that are different from each other and for this reason, each of them can be separated. However, such atoms cannot be separated further without provoking a nuclear reaction. The molecules can have properties very different from those that have the elements that compose it. For example, water behaves very differently than oxygen and hydrogen.

On the other hand, a single atom cannot exist independently in nature (without joining something). For example, we will never find a single atom of oxygen, it is always attached to something (oxygen = O2). When molecules are formed, they can exist independently in nature; so we can always find a molecule of oxygen, carbon or water. The atoms of the molecules are adhered to each other in a particular way, depending on the amount of bonds that the atom can make. Because of this the molecules can have hexagonal, pentagonal forms.

Finally, molecules tend to cluster and their formation depends on their state. For example, in a gaseous state, molecules usually fly around. In the liquid state, the molecules tend to be loosely grouped; reason why they can move. While in solid state, the molecules are tighter or close together and can only vibrate.

Generally, molecules are represented in a molecular formula. For example: C6H12O6 (sugar). This molecular formula is nothing more than the name of the element, followed by the number of atoms of that element in the molecule.

Key differences between Atom and Molecule

  • Atoms are constituents of matter, while molecules are made up of atoms different from each other.
  • Atoms are not independently in nature, but molecules can be.