Anything that has mass and occupies space is called matter. The matter is made up of atoms. Atomic structure is the structure of an atom that consists of a nucleus (the centre), protons (positively charged), and neutrons (neutral). The electrons are negatively charged particles that orbit the nucleus’s centre.

Democritus came up with the concept that matter is composed of atoms. John Dalton, in 1800 proposed the first scientific theory of atomic structure. In the article. We will learn the structure of an atom, subatomic particle, discovery, properties with some examples.

What is an Atom?

Atoms are the building blocks of matter. Therefore, the existence of different kinds of matter around us is due to atoms present. The idea of the relativity of matter was considered run back in India around \(500\,{\rm{BC}}\). The Indian philosopher Maharshi Kanad postulated that if we go on the dividing matter (padarth), we get smaller and smaller particles.

Ultimately, we will get the smallest particle, which cannot be divided further. He named these ultimate particles parmanu. The ancient Greek philosophers like Leucippus, Democritus and Epicurus suggested that subdivision of matter is possible. If we go on dividing the matter, a stage will come when particles cannot be further divided. They called these indivisible particles atoms. The word atom comes from a Greek word, something which cannot be split, i.e., indivisible.

Study of Structure of Matter

The first evidence-based theory on the structure of the atom was given by John Dalton, known as Dalton’s Atomic theory, in the year \(1808\). According to this theory, the smallest and the ultimate particle of matter is an atom. However, towards the end of the \({19^{{\rm{th}}}}\) century and at the beginning of the \(20{\rm{th}}\) century, scientists like J.J. Thomson, Goldstein, Rutherford, Chadwick, Bohr and many more, as a result of their researchers, established that the atom is not as simple as suggested by Dalton.

Atom is made up of \(36\) subatomic particles, out of which the most important are the electrons, protons, and neutrons. These three particles are called elementary fundamental particles of an atom because these are essential constituents of atoms.

The particles are held within the atom by one of the four fundamental forces- gravity, electromagnetic force, strong force, and weak force.

Parts of an Atom

An atom consists of two parts. These are the nucleus and extranuclear portions. The nucleus is present in the centre of the atom and is surrounded by the extranuclear portions. The radius of the nucleus of an atom is nearly \({10^{ – 15}}\;{\rm{m}}\), while that of the atom is \({10^{ – 10}}\;{\rm{m}}\).

The mass of the atom is mainly due to the nucleus, i.e., the atomic mass number is equal to the number of protons and neutrons present in the nucleus. Protons and neutrons together are called nucleons. The nucleus is positively charged since the protons are positively charged and the neutrons are neutral.

All the electrons are present in extranuclear space around the nucleus, revolve in well-defined circular paths known as orbits. The orbits are also called energy levels or energy shells, and these are designated as \({\rm{K}},\,{\rm{L}},\,{\rm{M}},\,{\rm{N}},\,{\rm{O}},\, \ldots \) The order of the energy of these energy shells is \({\rm{K}} < {\rm{L}} < {\rm{M}} < {\rm{N}} < {\rm{O}},\, \ldots \) Electrons when revolving around the nucleus do not lose or gain energy. Thus, the energy of electrons remains stationary.

The total positive charge of the nucleus is due to the presence of protons is the same as that of the negative charge of electrons present in the extranuclear space, therefore, the atom as a whole is electrically neutral.

Electrons

The smallest particle of an atom that has a negative charge on it is called electrons. It revolves around the nucleus in a circular path in an atom and is represented by \({{\rm{e}}^ – }\). In the \(1897\), the electron was discovered by J.J Thomson through his cathode ray experiment.

Characteristics of Electrons

1. The mass of an electron is \(\frac{1}{{1837}}\), the mass of a hydrogen atom or equal to \(9.1 \times {10^{ – 31}}\;{\rm{kg}}\).
2. An electron carries a unit negative charge with a magnitude of \(1.602 \times {10^{ – 19}}\) coulombs.
3. The radius of the electron is extremely small, i.e., less than \({10^{ – 15}}\;{\rm{m}}\).

Protons

The particles of an atom, which is present in the nucleus having a positive charge on them, are called protons. It is presented as \({{\rm{p}}^{\rm{ + }}}\). Goldstein discovered a positively charged particle, but the credit for the discovery of protons is given to Ernest Rutherford.

Characteristics of Protons

1. The mass of the proton is the same as that of a hydrogen atom, i.e., \(1837\) times the mass of an electron, i.e., \(1.672 \times {10^{ – 27}}\;{\rm{kg}}\).
2. A proton carries a unit positive charge with a magnitude of \(1.602 \times {10^{ – 19}}{\rm{C}}\).
3. The proton is present in the nucleus of an atom.

Charge on Neutrons

The particles of an atom without any charge are called neutrons, and it resides in the nucleus of an atom. The mass of the neutron is almost equal to the mass of the proton. It is usually represented by \({\rm{n}}\) or \({{\rm{n}}^{\rm{0}}}\).

In the year (1932), Chadwick discovered new particles without any charge, on bombarding light nuclei atom-beryllium with alpha particles and were thus named neutrons.

Characteristics of Neutrons

1. These do not have any charge on them and are thus named neutrons.
2. Neutrons are neutral molecules, hence does not deflected by an electric or magnetic field.
3. Its mass is equal to \(1.675 \times {10^{ – 27}}\;{\rm{kg}}\).

Atomic Structure of Nitrogen

The nitrogen \(\left( {\rm{N}} \right)\) is made of \(7\) protons, \(7\) electrons and \(7\) neutrons. Electrons are revolving around the central nucleus in the circular path. Since the number of protons is equal to the number of neutrons, the nitrogen atom is electrically neutral.

Atomic Structure of Hydrogen, Oxygen, and Carbon

The hydrogen \(\left( {\rm{H}} \right)\) is made of \(1\) proton and \(1\) electron. Electrons revolve around the central nucleus in the circular path.

The oxygen \(\left( {\rm{O}} \right)\) is made of \(8\) protons, \(8\) electrons and \(8\) neutrons. Electrons are revolving around the central nucleus in the circular path. Since the number of protons is equal to the number of neutrons, the oxygen atom is electrically neutral.  

The carbon \(\left( {\rm{C}} \right)\) is made of \(6\) protons, \(6\) electrons and \(6\) neutrons. Electrons are revolving around the central nucleus in the circular path. Since the number of protons is equal to the number of neutrons, the carbon atom is electrically neutral.  

The atomic structure of hydrogen, oxygen and nitrogen are represented as follows:

Types of Atoms

Following are the different types of atoms.

1. Stable: Atoms with protons, electrons, and neutrons in balance are stable atoms.
2. Isotopes: Elements with the same number of protons but different neutrons are called isotopes. It is also defined as elements with the same atomic number but with different mass numbers.
   Example: Isotopes of hydrogen are protium \(\left( {_1^1{\rm{H}}} \right)\), deuterium \(\left( {_1^2{\rm{H}}} \right)\), and tritium \(\left( {_1^3{\rm{H}}} \right)\).
3. Radioactive: An atom is unstable due to too many neutrons, and is radioactive in nature.
   Example: Uranium
4. Antimatter: These are atoms with a twin anti-particle with an opposite electric charge. It is very rare and fragile.
5. Ions: Atoms with less or a greater number of electrons than that of protons, forms ions.

Summary

In this article, the structure of an atom, you have understood what an atom is, the parts of a bit, the properties of the fundamental particles of an atom, i.e., protons, electrons, and neutrons. With examples of carbon-nitrogen provided on this page, you can explain the structure of an atom. This article is also helping in recollecting the different types of atoms and their meaning.

FAQs

Q.1. What do you mean by the structure of an atom?
Ans: An atom consists of two parts: the nucleus and extranuclear portions. The nucleus is present in the centre of the atom and is surrounded by the extranuclear portions. Protons and neutrons reside in the nucleus and are together called nucleons. The nucleus is positively charged since the proton is positively charged and the neutron is neutral. The electrons are negatively charged and present in extranuclear space around the nucleus. Electrons revolve in well-defined circular paths known as orbits.  

Q.2. What are the structures and properties of an atom?
Ans: Structure of atom: An atom consists of two parts. These are the nucleus and extranuclear portions. The nucleus is present in the centre of the atom and is surrounded by the extranuclear portions. Protons and neutrons reside in the nucleus. The electrons are present in extranuclear space around the nucleus. Electrons revolve in well-defined circular paths known as orbits.  
Properties of Atom:
1. An atom consists of three elementary subatomic particles, i.e., protons, electrons, and neutrons.
2. Protons and neutrons reside in the nucleus and are together called nucleons.
3. The nucleus is positively charged since the proton is positively charged and the neutron is neutral.
4. The electrons are negatively charged.
5. Atoms are neutral as a whole.

Q.3. How do you know the structure of an atom?
Ans: The structure of an atom can be known by the atomic number and mass number. The atomic number is equal to the number of protons, and the number of protons is equal to the number of electrons in a neutral atom. The mass number gives the number of neutrons and protons in an atom. The mass number is equal to the sum of the number of protons and neutrons.

Q.4. What are the two parts of an atom?
Ans: An atom consists of the following parts, i.e., nucleus, extranuclear portions. The nucleus consists of protons and neutrons. All the electrons are present in extranuclear space around the nucleus, revolve in well-defined circular paths known as orbits.

Q.5. What are the four types of atoms?
Ans: The four types of atoms are stable atoms, isotopes, radioactive atoms and antimatter.

We hope this article on the structure of an atom has helped you. If you have any queries, drop a comment below and we will get back to you.