Thomson discovered the first subatomic particle, the electron, while researching cathode rays. To explain the neutrality of atoms, Thomson proposed a model of the atom in which negative electrons are scattered throughout a sphere of positive charge. He called his atom the plum pudding model.

Thomson’s Plum Pudding Model Explained

The Thomson’s plum pudding model was proposed by J.J. Thomson in 1904 as an atomic model to explain the structure of an atom. This model was proposed before the discovery of protons and neutrons, so it was based on the knowledge available at that time. The model consisted of a positively charged sphere with negatively charged electrons embedded in it, much like plums in a pudding.

Existence of Protons

The existence of protons can be inferred from the results of the experiments conducted by Ernest Rutherford in 1911, known as the gold foil experiment. In this experiment, a beam of alpha particles was directed towards a thin gold foil. According to Thomson's plum pudding model, the positive charge was expected to be evenly distributed throughout the atom. However, Rutherford observed that some alpha particles were deflected at large angles, and a few even bounced back. This led to the conclusion that there must be a small, dense, positively charged nucleus at the center of the atom. This nucleus was later identified as protons.

Electrical Neutrality of an Atom

The electrical neutrality of an atom refers to the equal balance of positive and negative charges within the atom. According to Thomson's plum pudding model, the positive charge was assumed to be uniformly distributed throughout the atom, while the negatively charged electrons were embedded within it. This distribution of charges resulted in an overall neutral atom, as the positive and negative charges canceled each other out.

Existence of Electrons

Thomson's plum pudding model proposed the existence of electrons within the atom. These negatively charged particles were embedded within the positively charged sphere, much like plums in a pudding. The model suggested that electrons were distributed throughout the atom, providing the negative charge necessary to balance the positive charge.

Electrons Move in Fixed Circular Orbits

Contrary to the statement given, Thomson's plum pudding model did not propose that electrons move in fixed circular orbits. It was Niels Bohr who later proposed the concept of electrons moving in fixed energy levels or shells around the nucleus, which was an advancement from Thomson's model.

In conclusion, the Thomson's plum pudding model explained the existence of protons, the electrical neutrality of an atom, and the existence of electrons. However, it did not propose that electrons move in fixed circular orbits.

An atom consists of a positively charged sphere with electrons filled into it. The negative and positive charges present inside an atom are equal and as a whole, an atom is electrically neutral.

Thomson’s model of the atom as compared to plum pudding and watermelon.

He compared the red edible part of the watermelon to a positively charged sphere whereas the seeds of watermelon to negatively charged particles.