An atom is the smallest particle of an element that cannot be broken down by normal chemical methods. Every atom has two main parts — the nucleus and the electron shells.

The nucleus is at the center and contains protons (positive charge) and neutrons (no charge). Together, they make the nucleus heavy.

Electrons (negative charge) move around the nucleus in fixed paths called shells or energy levels. Each shell can hold a certain number of electrons.

This whole arrangement of protons, neutrons, and electrons is called the structure of an atom.