Introduction

Atomic structure is the structure of an atom that consists of a nucleus (the center), protons (positively charged) and neutrons (neutral). The electrons, which are negatively charged particles, circle around the nucleus’s center.

The origins of atomic structure and quantum mechanics can be traced back to Democritus, the first person to postulate that matter is made up of atoms. Studying an atom’s structure provides a wealth of information on chemical processes, bonds, and physical properties. In the 1800s, John Dalton proposed the first scientific theory of atomic structure.

What is Atomic Structure?

The atomic structure of an element refers to the nucleus’ composition and the arrangement of electrons around it. The building components of matter’s atomic structure are protons, electrons, and neutrons.

The atom’s nucleus comprises protons and neutrons, and electrons surround it. The atomic number describes the total number of protons in its nucleus.

Neutral atoms have an equal number of protons and electrons. Atoms, on the other hand, can gain or lose electrons to improve their stability, resulting in a charged object known as an ion.

The atomic structures of different elements differ because they have different numbers of protons and electrons. This is why different elements have different properties.

Basic Properties

Here are the basic properties of the structure of the atom;

• Atomic number

The atomic number (typically denoted by the letter Z) is defined as the number of units of positive charge (protons) in the nucleus. It is the single most essential feature of an atom.

• Atomic Mass And Isotopes

The mass of an atom is affected by the number of neutrons in its nucleus, but not its chemical characteristics. As a result, a nucleus with six protons and six neutrons will have the same chemical characteristics as a nucleus with six protons and eight neutrons, despite their different masses.

• The Electron

The mass of an electron is approximately 9.109382911 1028 grams. A proton or neutron has a mass of about 1,836 times an electron. This explains why the mass of the protons and neutrons in the nucleus determines the mass of an atom.

Atomic Models

Many scientists attempted to describe the structure of the atom using atomic models in the 18th and 19th centuries. Each of these models had its advantages and disadvantages, and they were all important in creating the present atomic model. Scientists including John Dalton, J.J. Thomson, Ernest Rutherford, and Niels Bohr made significant contributions to the discipline. This section delves into their theories about the structure of the atom.

Dalton’s Atomic Theory

All matter, according to English chemist John Dalton, is made up of indivisible and indestructible atoms. He also claimed that all atoms of a given element were the same but that the size and mass of atoms of different elements differed.

According to Dalton’s atomic theory, chemical reactions require the rearrangement of atoms to generate products. The atomic structure, according to Dalton’s postulates, was made up of atoms, the smallest particles responsible for chemical reactions.

The following are his theory’s postulates:

• Atoms are the building blocks of all matter.
• Atoms are unbreakable.
• Certain elements have only one sort of atom.
• Each atom has a constant mass, which varies depending on the element.
• During a chemical reaction, atoms rearrange themselves.

Demerits of Dalton’s Atomic Theory

The idea did not explain the occurrence of isotopes.

Nothing concerning the atom’s structure was adequately explained.

Scientists later identified particles inside the atom, proving that atoms are divisible.

The discovery of subatomic particles inside atoms led to a better understanding of chemical species. The following is a list of subatomic particles that have been discovered:

Thomson Atomic Model

In the early 1900s, English chemist Sir Joseph John Thomson proposed his model for defining atomic structure.

For the discovery of “electrons,” he was later awarded the Nobel Prize. His research is based on a technique known as the cathode ray experiment. 

Limitations 

• Thomson’s atomic model did not explain how the positive charge holds on the electrons in  the atom.
• The theory did not tell anything about the nucleus of an atom. It did not explain the scattering experiment of Rutherford.

Cathode Ray Experiment

It features a glass tube with two openings: one for the vacuum pump and the gas input.

Observations:

Rays emerged from the cathode towards the anode when a high voltage power supply was turned on. The ‘Fluorescent dots’ on the ZnS screen demonstrated this. “Cathode Rays” were the name given to these rays.

The cathode rays are bent towards the positive electrode when an external electric field is introduced, but they move straight when there is no electric field.

Rotor Blades appear to rotate when they are put in the path of the cathode rays. This demonstrates that cathode rays are composed of particles of a specific mass, and so have energy.

Rutherford’s Structure of Atom

Rutherford postulated in 1911, the following structure of the atom based on the previous observations and conclusions.

• The nucleus is the center of an atom, containing most of the charge and mass.
• Spherical atomic structure.
• Electrons have a circular orbit around the nucleus, similar to how planets circle the sun.

Limitations of Rutherford Atomic Model

If electrons must revolve around the nucleus, they will expend energy, which will be wasted against the vital force of attraction from the nucleus. Electrons will finally lose all of their energy and fall into the nucleus, leaving the atom’s stability unaffected.

The type of spectrum expected is a continuous spectrum if electrons continue to spin around the nucleus. However, what we see is a line spectrum.

Conclusion 

The atomic structure of an element refers to the nucleus’ composition and the arrangement of electrons around it. The building components of matter’s atomic structure are protons, electrons, and neutrons.  Scientists including John Dalton, J.J. Thomson, Ernest Rutherford, and Niels Bohr made significant contributions to the discipline. The type of spectrum expected is a continuous spectrum if electrons continue to spin around the nucleus. However, what we see is a line spectrum.