Structure of Atom

The structure of atom is a complex arrangement of negatively charged electrons organized in defined shells around a positively charged nucleus. The image of the electrons is shown below showing positively charged nuclei and negatively charged electrons revolving about the nucleus in their fixed orbit.

This nucleus, which is made up of protons and neutrons, contains the majority of the atom’s mass (except for common hydrogen which has only one proton). Every atom is roughly the same size. The Angstrom (Å), defined as 1 x 10^-10 m, is a useful unit of length for measuring atomic sizes. An atom has a diameter of about 2-3 Å.

Protons

A proton is a stable subatomic particle with a positive electric charge. Protons reside in the nucleus of every atom, determining its atomic number. This number also dictates the count of atomic electrons and the element’s chemical properties.

Comparatively, protons are slightly less massive than neutrons but 1,836 times more massive than electrons. Protons and neutrons together form nucleons.

The term “proton” originates from the Greek word meaning “first”. Ernest Rutherford coined the term “proton” for the hydrogen nucleus in 1920.

Positively charged, protons are particles of matter used in radiation treatment. Specially designed equipment can generate streams of protons for this purpose.

Neutrons

Neutrons are subatomic particles present in the nucleus of every atom, except hydrogen. Electrically neutral, they carry no charge and have a mass slightly greater than a proton.

When bound in an atomic nucleus, neutrons remain stable. However, as free particles, they have an average lifetime of approximately 1,000 seconds.

Neutrons, alongside protons and electrons, constitute the trio of subatomic particles within an atom. While protons bear a positive charge and electrons a negative one, neutrons maintain neutrality.

Isotopes refer to atoms of the same chemical element differing only in neutron number. For instance, carbon-12 contains 6 neutrons, whereas carbon-13 contains 7.

James Chadwick discovered neutrons in 1932.

Electrons

Electrons are negatively charged subatomic particles and belong to the first generation of the lepton particle family. They are considered elementary particles, lacking any known substructure or components.

Electrons can exist either bound to an atom or in a free state. When bound, they constitute one of the three primary particle types within the atom, alongside protons and neutrons, forming the atom’s nucleus.

Compared to other components of an atom, electrons are extremely small. While the charge of an electron equals that of a proton in magnitude, it bears the opposite sign. Therefore, electrically neutral atoms and molecules possess an equal count of electrons and protons.

Due to opposite charges, electrons are attracted to protons. Collectively, the electrons in an atom create a negative charge that offsets the positive charge of the protons in the atomic nucleus.

Joseph John Thomson discovered the electron in 1897.

The nucleus of an atom is a small, dense, round region located in the centre of an atom. It has two subatomic particles, protons and neutrons. Protons are electrically positively charged ions having a mass of approximately one atomic mass unit (amu). Neutrons are electrically neutral.

The atomic nucleus is bonded together by the strong force (also known as nuclear force), the most powerful known fundamental force in nature. The atomic nuclei have more than 99.9% of the atomic mass and are 10,000 times smaller. In 1911, Ernest Rutherford discovered the nucleus of an atom.

Before learning about the Nucleus we first need to learn about the Structure of atoms in brief so let’s start with that.