J J Thomson's Atomic Model and Its Limitations

Introduction

British researcher J.J. Thomson revealed that the atom was made up of many tiny components designed to transport electrical charge. During Thomson's study, scientists believed that atoms were fundamentally neutral. Thomson claimed that atoms included microscopic -ve particles floating over a +ve charged fluid. The plum pudding model is another name for this model.

What do we understand by an Atomic Model?

The atomic model is the framework that describes the composition & structure of the atom, and it has evolved over the years. The atom has been extensively studied as a constituent of the cosmos to comprehend how atoms comprise the universe. Throughout time, five main models of the atom have been presented, each of which is tied to the study of the atom over the period. Bohr's atomic model, the Quantum atomic model, Thomson's atomic model (also known as the plum pudding model), Dalton's atomic model, as well as Rutherford's atomic model are the five models of the atom.

Plum Pudding Model

J. J. Thomson, who developed the e^- in the year 1897, suggested the plum pudding model of the atom for incorporating the e^- in the atomic model in the year 1904. In this idea, electrons were supposed to be arranged in circular rings all around the atom to form a "cloud" of +ve charge. An atom was believed to be composed of a +ve charge sphere with an e^- embedded within it. The -ve, as well as +ve charges, were identical in size. The atom as a whole was electrically neutral. However, while Thomson's hypothesis acknowledged why atoms are electrically neutral, it did not clarify the observations undertaken by other researchers.

What are the postulates of JJ Thomson?

• The atom is neutrally charged.

• There is a supply of +ve charge which cancels out electrons' -ve charge.

• This +ve charge is spread equally across the atom.

• According to Thomson, "negatively electrified corpuscles," or even electrons, are trapped inside the homogeneous bulk of +ve charge.

• Electrons can travel freely throughout the atom.

• The electrons possessed stable orbits, according to Gaussian Law. If the e^- travelled through the +ve "mass," the +ve charge that spontaneously generated around the orbit neutralised their internal forces. In the UK, the atomic model was widely termed as a plum pudding model since the pattern anticipated by Thomson was closely similar to the packing of plums.

Limitations of JJ Thomson Model of Atom (Plum Pudding Model)

• It didn't address atomic stability since his atomic model couldn't justify how a +ve charge could keep -ve charge e^- in an atom. As a consequence, this concept also did not demonstrate the location of an atom's nucleus.

• His model fails to clarify how thin metal foils might generate alpha particle dispersion.

• There is no experimental data to back up the claim.

• His model served as the foundation for the creation of subsequent atomic models, even though it is not a realistic model for accounting for atomic structure. The research of the atom and its structure set the door for countless subsequent breakthroughs that have played an important part in the progress of science.

How did J.J Thomson change Dalton’s atomic theory?

All elements in the universe, as per Dalton's atomic theory, is made up of tiny substances that are not visible to the human eye. These substances were thought to be atoms.

• It was incorrect to state that atoms are indivisible. The atom can be split more into protons, electrons, as well as neutrons.

• As per Dalton's hypothesis, atoms of the same element are identical in every way, while atoms of other elements differ in their weights but also densities.

• The occurrence of allotropes is not explained by the hypothesis. Thomson updated the atomic hypothesis, defining atoms as evenly packed spheres holding positively charged substances loaded with negatively charged electrons.

Conclusion

This tutorial focuses on the atomic model given by the scientist J.J Thomson commonly referred to as the plum pudding model as well as the restrictions it faces. J.J Thomson related his design to a watermelon. His model couldn't justify how +ve charge maintains the -ve charge electrons in the atom, hence he couldn't explain atomic stability. He doesn't clarify how thin metal foils scattered alpha particles.

FAQs

1.Illustrate how an atom is neutral as a whole using the plum pudding model.

According to the plum pudding model, an atom is essentially a +ve charged sphere into which -ve charged e_- are inserted. Because the charges are of similar size, they balance each other out as well as neutralise the atom.

2.Describe the main disadvantage of the plum pudding model.

Although this model was acknowledged at the moment, it was quickly abandoned since it could not achieve atomic stability as it cannot justify how the -ve charged e_- is confined within the +ve sphere. In other terms, it could not account for the existence of a nucleus in an atom.

3.Describe the chemical combination laws.

As per the Law of Conservation of Mass, no mass can be generated or dissipated in a chemical reaction if the chemical system is separated from all outside forms of energy as well as heat. As a result, the amount of mass is preserved over the years.

As per the Law of Constant Proportions, the constituents of a chemical complex are always existing in the fixed ratio by mass. It indicates that every pure complex will always have similar components in the same proportion by mass.

4.The scientist J.J. Thomson, did he discover the atomic nucleus?

He discovered the e_- in the year 1897 as well as presented the plum pudding model in the year 1904 before discovering the nucleus to incorporate the e_- in the atomic model. He was not the first to identify the atomic nucleus. Ernest Rutherford, another scientist, found it throughout his tin foil study.

5.How can it be demonstrated that matter is composed of electrically charged particles?

• Brush your hair and lay the hairbrush near some little scraps of paper. Papers particle adheres to the hairbrush. Brushing the hair transfers some of the hair's subatomic components termed e_- to the brush. Because an e_- has a -ve charge, the hairbrush will also acquire the charge of an e_- (that is -ve). Lastly, bringing the hairbrush close to the scraps of paper will attract the scraps of paper to the brush.

• Place a glass rod near an enlarged balloon after rubbing it with a silk cloth. Electrons go from the glass rod to the silk cloth. Therefore, the glass rod now has a +ve charge. The +ve charged glass rod is pulled to the enlarged balloon when it is introduced near to it.