What is a Molecule?

Molecule Definition

A molecule is defined as the smallest unit of a compound that contains the chemical properties of the compound.

Molecules are made up of groups of atoms. Describing the structure of an atom, an atom is also sub-divided into smaller units. Protons, electrons, and neutrons are sub-particles of an atom. The protons and neutrons are contained inside the nucleus of the atom and electrons revolve around the nucleus.

Protons are positively charged particles whereas electrons are negatively charged particles. Neutrons do not carry any charge. So we can say that the nucleus is positively charged due to the presence of protons. The nucleus is a bulk mass at the centre of an atom. Atoms are largely vacant.

Every element has a certain atomic number. The atomic number of an element is defined as the number of protons present in its nucleus. It is denoted by Z.

When we talk about the mass of atoms, the mass of their particles is taken into consideration. Electrons have negligible mass. Hence the mass of an atom is the sum of the mass of protons and neutrons. The mass number is denoted by A.

A molecule is the smallest unit (particle) of a compound having the physical and chemical properties of that compound. This does not mean that molecules can not be broken down into smaller parts, e.g. the atoms from which they are formed or the fragments of the molecule, each consisting of several atoms or parts of atoms.

A molecule is defined as the smallest unit of a compound that contains the chemical properties of the compound. Molecules are made up of groups of atoms. Describing the structure of an atom, an atom is also sub-divided into smaller units. Proton, electrons, and neutrons are sub-particles of an atom. The protons and neutrons are contained inside the nucleus of the atom and electrons revolve around the nucleus.

Examples of Molecules

A molecule is a collection of two or more atoms that make up the smallest recognisable unit into which a pure material may be split while maintaining its makeup and chemical characteristics. Some examples of molecules are

• H₂O (water)
• N₂ (nitrogen)
• O₃ (ozone)
• CaO (calcium oxide)
• C₆H₁₂O₆ (glucose, a type of sugar)
• NaCl (table salt)

Forces between Atoms and Molecules

The simplest forces between atoms are those which arise as a result of electron transfer. A simple example is that of say sodium fluoride. The sodium atom has a nuclear charge of +11, with 2 electrons in the K shell, 8 in the L shell and 1 in the M shell. The fluorine atom has a nuclear charge of 9 with 2 electrons in the K shell and 7 in the L shell.

The outermost electron in the sodium atom may transfer readily to the fluorine atom; both atoms then have a complete shell but the sodium now has a net charge of +1 and the fluorine a net charge of -1. These ions, therefore, attract one another by direct coulombic interaction. The force between them is strong it varies as x-2, where x is the distance between the ions, and it acts in the direction of the line joining the ions.