Structure of The Atom in Science

All matter is made up of tiny particles called atoms. Earlier, it was believed that atoms could not be divided further, but later it was discovered that atoms are made up of three smaller particles — electrons, protons, and neutrons.

Electrons are negatively charged particles discovered by J.J. Thomson through the cathode ray experiment.
Protons are positively charged particles discovered by E. Goldstein through the canal ray experiment.
Neutrons are neutral particles discovered by James Chadwick.

Several models were proposed to explain the structure of the atom.

Thomson’s model suggested that an atom is a positively charged sphere in which electrons are embedded like plums in a pudding. This model could not explain how atoms show stability.

Rutherford’s model  was based on the alpha particle scattering experiment. He concluded that an atom has a small, dense, positively charged nucleus at its center and that electrons revolve around the nucleus. However, this model could not explain why electrons do not fall into the nucleus.

Bohr’s model explained that electrons revolve around the nucleus in fixed paths or orbits called energy levels or shells. Each shell has a fixed energy, and electrons can move from one shell to another by gaining or losing energy.

The atomic number (Z) is the number of protons in an atom. The mass number (A) is the sum of protons and neutrons.
A = Z + Number of neutrons.

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons, for example, ¹H, ²H, and ³H.
Isobars are atoms of different elements that have the same mass number but different atomic numbers, such as ⁴⁰Ar and ⁴⁰Ca.

According to the Bohr–Bury rule, the maximum number of electrons that can be present in a shell is 2n², where n is the shell number.
K shell can have 2 electrons, L shell 8, and M shell 18 electrons. The outermost shell can have a maximum of 8 electrons.

Valency is the combining capacity of an atom and is determined by the number of electrons in the outermost shell. For example, hydrogen has a valency of 1, oxygen 2, and carbon 4.

The electronic configuration shows how electrons are arranged in different shells. For example:
Hydrogen – 1; Helium – 2; Carbon – 2,4; Oxygen – 2,6; Sodium – 2,8,1.

In conclusion, an atom consists of a nucleus containing protons and neutrons, with electrons revolving around it in fixed energy levels. Atoms are electrically neutral because the number of protons equals the number of electrons.