Atomic Structure

How to calculate electron,proton & neutron?

Atom is the smallest particle of an element.It represents the properties of that element.

In beginning, scientist proposed that atoms(from the Greek word “atomos” means indivisible) are the fundamental building blocks of matter. According to them, atom can not be further divisible. Everything in the universe is made of matter, and, so, everything in the universe is made of atoms.

Atoms of the same element are identical. Atoms of any one element are different from those of any other element.In a chemical reactions, atoms are combined or  separated but not changed into atoms of another element.

Atomic Structure

Subatomic Particle

An atom is made up of particles called subatomic particles: protons, neutrons, and electrons. The protons and the neutrons reside in the nucleus and the electrons revolve around above the nucleus in a small cloud . The electrons carry a negative charge and the protons carry a positive charge. In a neutral condition, atom carry the equal number of protons and electrons.


It contains positive charge.Mass of the atom was densely concentrated in extremely small region. This very small portion of the atom was called nucleus.Nucleus contains protons and neutron (collectively known as nucleon).

Orbit / Shell

Electrons move around the nucleus with a very high speed in circular paths called shell / orbit.

It is the virtual path followed by the electrons around the nucleus.

valence shell

Outermost shell is called valence shell.

electrons in the outermost shell determine the chemical properties of the atom.


The number of electrons that must be lost or gained by an atom to obtain a stable electron configuration.

It is the capacity of an atom of a single element to react and combine with particular numbers of atoms of another element. The valence electrons take part in any chemical reaction.


Ion is a charged atom. When the number of electrons are equal to the number of protons,that atom is called ion. An atom can acquire a positive charge or a negative charge depending on whether the number of electrons in an atom is decreased or increase.

Negatively charged ions are called anions, and positively charged ions are called cations.

Atomic Number

The number of protons / Electron present in atom is equal to atomic number (Z ). For example, the number of protons in the hydrogen nucleus is 1, in sodium atom is 11.

Atomic number (Z) = Number of protons in the nucleus of an atom or number of electrons in shells of a neutral atom.

Mass Number

The total number of nucleons (Proton and Neutron) is termed as mass number (A) of the atom.

mass number (A) = number of protons (Z) + number of neutrons (n)

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