Neutrons - The Neutral Sub-Atomic Particle

What are Neutrons?

An atom is the smallest unit of matter. It is composed of sub-atomic particles, for example, neutrons, protons, and electrons. The entire mass of an atom is concentrated in the nucleus which is at the center of an atom. The nucleus contains protons and neutrons which are collectively known as nucleons. Electrons revolve around the nucleus of an atom in circular paths. Protons are positively charged particles and electrons are negatively charged particles. The magnitude of this charge is same for both electrons and protons. Neutrons carry no charge. Hence an atom is electrically neutral in nature.

Discovery of Neutron

Rutherford found that except the hydrogen atom, the atomic mass of other elements could not be explained on the basis of only electrons and protons. For instance, the atomic mass of a helium atom should be double that of a hydrogen atom. The e/m ratio (charge to mass ratio)  was calculated for helium atom. It was discovered that the mass of helium ion was four times the mass of hydrogen atom.

To explain this Rutherford predicted the presence of a particle other than electrons and protons in an atom. According to him such a particle should be electrically neutral and have the mass equal to that of a proton. Later, James Chadwick confirmed the presence of neutrons from his experiment based on the interaction of alpha particles with beryllium.

Properties of Neutrons

  • Mass of neutron – The mass of a neutron is equal to that of a proton. Electrons are considered to have negligible mass, the mass of an electron is 1/1840 times that of the proton. Thus,
    Mass of neutron = 1.676 × 10-27 kg = 1.676 × 10-24 g
  • The charge of a neutron – Neutrons do not carry any charge. Hence they are electrically neutral in nature.