What Is An Atom?

The smallest particle of an element, which may or may not have an independent existence, is called an atom. For example He, Ne, H, O. Atoms are the building blocks of matter. Atoms of helium, neon exists independently but atoms of hydrogen, nitrogen and oxygen cannot exist independently. Atom is composed of more than 100 sub atomics particles like electron, proton, neutron, hydrogen, neutrino, and antineutrino etc. however electron, proton and neutron are fundamental particles of the atom. The word atom is derived from "atomos" means indivisible but now atom is divisible.

                    A clear and accurate image of an atom can be observed in an electronic microscope. It uses beams of electrons and wavelength of electron us much shorter than that of visible light. Electronic microscope photograph of a piece of a graphite magnified about 15 millions times. The bright band in the figure is layers of carbon atoms. X-rays work shows that diameter of atom is 0.2 nm. Masses of atoms range from 10-27 to 10-25 kg. The masses of atoms are generally expressed in atomic mass units (a.m.u.) and 1 a.m.u. = 1.661*10-27 kg. The size of an atom is very small and a full stop contains about two million atoms.

The smallest particle of a substance is an atom.