An atom is the smallest unit of matter that has the properties of a chemical element. The size of an atom is around 100 picometers.

The atom contains 3 subatomic particles, known as neutrons, protons, and electrons, neutrally, positively and negatively charged respectively. The neutrons and protons exist in the nucleus of the atom, and the electrons orbit around the nucleus. The nucleus is a small dense area in the center of the atom.

The number of protons represents the Atomic Number of an atom, and the sum of both neutrons and protons reflects theMass numberof an atom. Since protons and electrons have an opposite charge, the difference in their number reflects their charge. Charged atoms are calledions.

Figure 1The identity of an Atom