Question

Which of the following observations match with Thomson's plum-pudding model of the atom?

• A. Elements are electrically neutral as a whole.
• B. Some elements, mostly metals, eject negative charges on heating.
• C. There exist heavy positively charged particles called protons.
• D. There are particles more fundamental than the atom itself.

Answer 1

Answer: (A), (B), (D)

The correct options are
A Elements are electrically neutral as a whole.
B Some elements, mostly metals, eject negative charges on heating.
D There are particles more fundamental than the atom itself.

J. J. Thomson's plum-pudding model proposes that the atom is a uniform distribution of positive charge, with the negative charged subatomic particles, or electrons embedded in the positively charged cloud, at points of stable equilibrium.

It explains -
a. Atoms are electrically neutral - the total number of negatively charged electrons exactly balance the positive charge of the cloud.
b.Elements on heating gets ionized when they receive sufficient energy and eject out their outermost electron in a process called Thermionic emission
c.Thomson didn't know about the existence of positively charged particles. He considered positive charges to be spread as a cloud instead of particles
d.Thomson's discovery of negatively charged particles coming out of electrically neutral atoms immediately suggested that atoms must be composed of negative and positive subatomic constituents.

So observations a, b, d are explained by Thomson's Plum Pudding Model. Only in hindsight of our deeper knowledge of atoms do we know that the model is not correct, but at that point, in the early 20th century, it seemed to many as a good model to explain a lot of observations, as we just saw.