What is Atom? Definition | Examples | Subatomic Particles

Definition of Atom:

“Atom is the smallest particle of an element, which can take part in a chemical reaction.”

The term “atom” comes from the Greek word “atomos” which means indivisible because it was once thought that atoms were the smallest things in the universe and could not be divided.
Atoms consist of a nucleus made of protons and neutrons orbited by electrons.


  • Here are some examples of atoms:
  • Neon (Ne)
  • Hydrogen (H)
  • Oxygen (O)
  • Nitrogen(N)
  • Uranium(U)

Sub-atomic Particles:

  • Modern researches have clearly shown that an atom is further composed of sub-atomic particles. “An atom itself is made up of three tiny kinds of particles called subatomic particles: protons, neutrons, and electrons”. More than 100 such particles are thought to exist in an atom. However, electrons, protons, and neutrons are regarded as the fundamental particles of atoms. Sub-atomic particles are:
  • Electron negatively charged particle.
  • Proton positively charged particle.
  • Neutron neutral particle..
  • Hyperion.
  • Neutrino.
  • Anti-Neutrino etc.


The protons and the neutrons make up the centre of the atom called the nucleus and the electrons fly around above the nucleus in a small cloud. The electrons carry a negative charge and the protons carry a positive charge. In a normal (neutral) atom the number of protons and the number of electrons are equal. Often, but not always, the number of neutrons is the same, too.

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