Atoms are known as the building blocks of matter. It is the smallest constituent unit of matter that possesses the properties of the chemical element. Atoms do not live individually; instead, they form ions and molecules that further aggregate in vast quantities to form matter that we see, sense and touch.

Atoms are too rare to be seen; thus, studies to figure out their structure and behaviour have to be performed with many of them. From these experiments’ results, we may try to create a hypothetical model of an atom that behaves like an actual atom.

The Greek philosopher Democritus proposed the theory of the atom around 450 B.C. In essence, however, the approach has been overlooked for more than 2000 years.

John Dalton reintroduced the atom in 1800. He has provided proof for the atoms and has established atomic theory. His principle is fundamentally correct. However, he was incorrect to think that atoms are the smallest particles of matter.

J.J. Thomson discovered electrons in 1897. He suggested the atom’s plum pudding concept. In this model, negative electrons are dispersed throughout the “sea” of a positive charge.

The credit for the discovery of the nucleus goes to Ernest Rutherford, who found the nucleus in 1911. He is also credited with the discovery of protons. Rutherford assumed that electrons would spontaneously circle the nucleus.

The physicist James Chadwick experimented in 1932. The subsequent radiation revealed an intense penetration through the lead shell, which could not be explained by the particles understood at the time. To show that the particle was a neutron, Chadwick weighed its mass. Instead, he weighed everything else about the collision and used the knowledge to quantify the mass. Chadwick bombed boron with alpha particles to test its density. Boron released neutral rays like beryllium.

Neil Bohr introduced the Bohr atom model in 1915. Bohr changed this structure of the atom by demonstrating that electrons pass in fixed orbitals and not somewhere in between. He also showed that each orbit has a fixed energy level. Rutherford essentially clarified the atom’s nucleus, and Bohr changed the model into electrons and their energy levels. The Bohr model is a small nucleus (positively charged) with negative electrons passing around the nucleus in orbits. Bohr observed that the electron positioned further from the nucleus had more energy, and the electrons around the nucleus had less energy.

The overall number of protons in the nucleus of an atom gives us the atom’s atomic number, represented with the letter ‘Z.’ All the atoms of a given element have the same number of protons and the same atomic number. Atoms and different elements have different atomic numbers. For example, all carbon atoms have an atomic number of 6, while all Oxygen atoms have 8 protons in their nucleus.

• Valence Electrons: Electrons in the unfilled outer shells are valence electrons.
• Isotopes: Isotopes may be classified as varieties of chemical elements with the same number of protons and electrons but a different number of neutrons. In other words, isotopes are types of elements that vary in their nucleon numbers owing to the difference in the overall number of neutrons in their respective nucleons.

In this chapter, we learned about the basic concepts of atomic structure and chemical bonding. The chapter also gave an understanding of concepts like isotopes and ionic electrovalency.

1. What are subatomic particles?
2. Subatomic particles are the particles that make up an atom. Generally speaking, this word refers to protons, electrons, and neutrons.
3. How do isotope atomic structures vary?
4. They differ in terms of the overall number of neutrons found in the atom’s nucleus represented by their nucleon numbers.
5. What are the drawbacks of the Bohr atomic model?
6. According to this atomic model, the structure of the atom gives weak spectral estimates of larger atoms. It also failed to clarify the influence of Zeeman. Only the hydrogen continuum is explained effectively.
7. How did Bohr find the electrons?
8. Bohr was the first to discover that electrons travel around the nucleus in various orbits and that the properties of the element are dictated by the number of electrons in the outer orbit.
9. Who found electrons?
10. J.J. Thomson discovered the electron in 1897 when he studied the properties of the cathode ray.