Thomson Atomic Models and their Limitations

Introduction

J.J. Thomson was a British physicist who was born on December 18, 1856, in Cheetham Hill, a Manchester suburb. In 1906, he was awarded the Nobel Prize in Physics for his contribution on the discovery of electrons. J.J. Thomson discovered the electron, a negatively charged particle, during a cathode ray tube experiment. A vacuum tube is a cathode ray tube. An electron was the name given to the negative particle. This experiment was carried out in the year 1897. Thomson compared the model of an atom he proposed to a Christmas pudding. The electrons in a positively charged sphere were like currants (dry fruits) in a spherical Christmas pudding. We may also conceive of this as a watermelon, with the positive charge in the atom scattered all over like the red edible portion of the watermelon, and the electrons lodged in the positively charged sphere like the seeds. He thought an atom was made up of thousands of electrons and that an electron was two thousand times lighter than a proton. In his atomic structure model, atoms were surrounded by a cloud with both positive and negative charges. Thomson was successful in describing an atom’s total neutrality.

Atomic Theory of Plum Pudding

Thomson claimed that the form of an atom is similar to that of a sphere with a radius of 10-10 m. The positively charged particles are dispersed equally, while the electrons are placed in such a way that the atom is electrostatically stable. Thomson’s atomic model was sometimes referred to as the plum pudding or watermelon model. The implanted electrons resembled the seed of a watermelon, and the red bulk of the watermelon reflected the positive charge distribution. The plum pudding atomic theory assumed that an atom’s mass is equally distributed across the atom.

Failure of Dalton’s Atomic Theory

According to Dalton’s atomic hypothesis, the atom is indivisible and indestructible. However, the atom’s discovery of electrons and protons caused this idea to collapse. The question of how these particles are organized within an atom arises. As a result, several scientists presented different atomic models. The first person to do so was J. J. Thomson. Atomic Structure: The finding of two basic particles (electrons and protons) inside the atom caused Dalton’s atomic theory to collapse. It was thought vital to understand how electrons and protons are ordered within an atom. Many scientists developed numerous atomic theories to explain this. J.J. Thomson was the first to suggest an atomic structure model.

Structure of Atom: The discovery of two basic particles (electrons and protons) inside the atom caused Dalton’s atomic theory to collapse. It was thought vital at the time to understand how electrons and protons are ordered within an atom. Many scientists developed numerous atomic theories to explain this. J.J. Thomson was the first to suggest an atomic structure model.

Thomson’s Atomic Model

Thomson proposed in 1897 that the fundamental body of an atom is spherical in form, with electrons (small particles within the atom that have a negative charge) and a positively charged “jelly” surrounding the electrons that neutralizes the charge of the electrons. The first portion of John Dalton’s theory is contradicted here since it claims that atoms are indivisible in nature, but Thomson discovered that there are other pieces to atoms, which he discovered to be electrons. So, in 1897, J.J. Thomson identified the first subatomic particle, the electron, as well as his new model. Thomson also helped to the discovery of isotopes and atoms having varied atomic weights of the same element.

Several scientists proposed many theories and explanations for the structure of an atom. J. J. Thomson, a scientist, developed the most basic model. Theoretically, this model described the description of the interior structure of the atom. Thomson’s model was not an accurate model for accounting for atomic structure, but it served as the foundation for the creation of alternative atomic models.

Thomson proposed that atoms are homogeneous spheres of positively charged substance embedded with electrons. The raisin pudding model, often known as the raisin pudding model, was abandoned (1911) for both theoretical and experimental grounds in favor of the Rutherford Atomic Model, in which electrons describe orbits around a tiny positive nucleus. Thomson’s atomic model, William Thomson (also known as Lord Kelvin) envisaged the atom as a sphere with an equally distributed positive charge and enough electrons embedded in it to neutralize positive charge.

The atom is structurally similar to a plum pudding, according to Thomson’s model. He envisioned electrons as dry fruits in a positive-charged sphere that represented the pudding. We may also relate this to a watermelon, with the positive charge dispersed throughout the edible area of the watermelon and electrons scattered in that sphere like seeds.

It is also possible to say that the electrons were randomly placed in a positively charged sphere. According to Thomas, the positive and negative charges were of equivalent magnitude, canceling each other out and neutralizing the atom.

Thomson’s Postulates 

• The atom is neutrally charged
• There is a source of positive charge that cancels out electron’s negative charge
• This positive charge is distributed evenly across the atom
• According to Thomson, “negatively electrified corpuscles,” or electrons, are trapped inside the homogeneous bulk of positive charge
• Electrons could freely move throughout the atom
• The electrons possessed stable orbits, according to Gaussian Law
• If the electrons went through the positive “mass,” their internal forces were balanced by the positive charge that was formed naturally around the orbit

J.J. Thomson’s atomic model was generally known as a plum pudding model in England because the electron distribution predicted by Thomson was comparable to the arrangement of plums in that delicacy

Thomson’s Atomic Model’s Limitations 

• This model was the most fundamental of all the others. It had many flaws, but it piqued the interest of other scientists and opened the path for additional important discoveries in the subject

• The presence of a nucleus in the atom was not mentioned in the model. It did not explain how the positive charge might contain the positively charged electrons

• In other words, it couldn’t account for the atom’s stability. It could not explain Rutherford’s scattering experiment and the scattering of alpha particles when projected on gold foils

• Thomson’s approach was a significant advance in the science of atomic chemistry. Despite major flaws, it served as a motivation for other researchers in the field to explore and come up with their conclusions and interpretations

Conclusion

Though obsolete by current standards, the Plum Pudding Model marks an essential milestone in the development of atomic theory. It included new findings, like the discovery of the electron, but it also established the atom as a non-inert, divisible mass.