Atoms are composed of subatomic particles, namely protons, neutrons, and electrons.
Protons are positively charged particles located in the nucleus, which is the central region of an atom. Each proton has a relative charge of +1 and a mass of approximately 1 atomic mass unit (amu).
Neutrons, on the other hand, are uncharged particles also located in the nucleus. They have a mass similar to that of a proton (approximately 1 amu), but they carry no electrical charge.
Electrons are negatively charged particles that orbit around the nucleus in specific energy levels called electron shells or orbitals. Electrons have a negligible mass compared to protons and neutrons. Each electron has a relative charge of -1 and contributes to the overall charge balance of the atom.
The number of protons determines the atomic number of an atom, which defines its elemental identity. For example, an atom with one proton is hydrogen, while an atom with six protons is carbon. Neutrons and electrons can vary in number within an atom of a given element without changing its identity. Atoms with the same number of protons but different numbers of neutrons are called isotopes.
The overall structure of an atom can be visualized as a tiny, dense nucleus at the center, consisting of protons and neutrons, surrounded by one or more electron shells, where the electrons reside. The electrons occupy specific energy levels based on their distance from the nucleus and follow certain rules and principles governed by quantum mechanics.