2.1.4. Discovery of Protons and Neutrons

Electrical discharge carried out in the modified cathode ray tube led to the discovery of canal rays carrying positively charged particles.

Canal rays were discovered when scientists conducted experiments using modified cathode ray tubes. Unlike cathode rays, which are negatively charged, canal rays consist of positively charged particles. This discovery was crucial in identifying the existence of protons, as canal rays are identified as positively charged gaseous ions.

Imagine you have a magnet and you notice that one side attracts metal while the other side repels it. Canal rays act like the attracting side of the magnet, highlighting the presence of positively charged particles in atoms.

The characteristics of these positively charged particles are listed below: (i) Unlike cathode rays, mass of positively charged particles depends upon the nature of gas present in the cathode ray tube. These are simply the positively charged gaseous ions. (ii) The charge to mass ratio of the particles depends on the gas from which these originate. (iii) Some of the positively charged particles carry a multiple of the fundamental unit of electrical charge. (iv) The behaviour of these particles in the magnetic or electrical field is opposite to that observed for electron or cathode rays.

The positively charged particles, known as protons, display unique characteristics compared to electrons (which make up cathode rays). The mass of these protons varies depending on the type of gas used in the cathode ray tube experiment. Additionally, some protons have a charge that is a multiple of the basic charge unit, and they behave differently than electrons when subject to magnetic or electrical fields.

Think of different types of balls; a soccer ball may weigh different amounts when inflated with different levels of air. Similarly, the mass and behavior of protons can vary based on the gases used in the experiments.

The smallest and lightest positive ion was obtained from hydrogen and was called proton. This positively charged particle was characterised in 1919.

The proton was identified as the smallest and lightest positively charged ion, and its discovery was a significant milestone in understanding atomic structure. This identification, finalized in 1919, confirmed that hydrogen consists of one proton, thus establishing protons as fundamental constituents of atomic nuclei.

Consider a Lego block set where one special block represents a proton. Just as every building starts with a single foundational block, every hydrogen atom starts with one proton as its basic unit.

Later, a need was felt for the presence of electrically neutral particle as one of the constituents of atom. These particles were discovered by Chadwick (1932) by bombarding a thin sheet of beryllium by α-particles. When electrically neutral particles having a mass slightly greater than that of protons were emitted. He named these particles as neutrons.

The discovery of neutrons was prompted by the understanding that atomic structure needed an electrically neutral particle to balance the positive charges of protons. Chadwick's 1932 experiments revealed neutrons as neutral particles slightly heavier than protons, which added stability to atomic nuclei by preventing protons from repelling each other due to their like charges.

Imagine a seesaw where one side is heavier due to several people balancing on it. Neutrons act like extra weight that keeps protons (the lighter side) from moving apart, ultimately stabilizing the atomic structure.

Thus, we can conclude that electrons are basic constituents of all the atoms.

In summary, various experiments conducted led to the understanding of atoms being made up of fundamental particles: electrons, protons, and neutrons. This discovery reshaped the early atomic theory, which depicted atoms as indivisible, by introducing a more complex structure of atomic components.

Think of atoms as buildings; while the outside might look like a single structure, if you look closer, you'll find many essential components like windows, doors, and rooms, analogous to how atoms consist of multiple fundamental particles.

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