Test: Atomic Structure - UPSC MCQ

Thomson's model of the atom, also known as the plum pudding model or Christmas pudding model, was proposed by J.J. Thomson in 1904. According to this model, the atom is composed of a positively charged "pudding" or sphere, with negatively charged electrons embedded within it like "plums" in a Christmas pudding. This model was later disproven by Rutherford's gold foil experiment, which led to the development of the modern atomic model known as the Rutherford model

Hydrogen is the only atom among the options listed that does not have any neutrons in its nucleus. The nucleus of a hydrogen atom consists of a single proton, which is positively charged, and it does not contain any neutrons. Neutrons are subatomic particles with no charge and are found in the nuclei of most other atoms.

According to Goldstein's experiment, which was conducted in the late 19th century, the discovery made was actually related to the existence of positively charged particles in a gas discharge tube. Wilhelm Wien later named these particles "protons."

In 1932, James Chadwick, an English physicist, discovered the neutron. He conducted a series of experiments involving the bombardment of beryllium with alpha particles, which led to the discovery of a neutral particle with a mass similar to that of a proton. This discovery provided crucial evidence for the existence of a neutral subatomic particle, the neutron, and contributed significantly to our understanding of atomic structure and nuclear reactions.

The correct electronic configuration of sodium is 2,8,1 (option A).

This means that sodium has 11 electrons. The first energy level can hold a maximum of 2 electrons, the second energy level can hold a maximum of 8 electrons, and the third energy level can hold a maximum of 8 electrons as well.

Therefore, the electronic configuration of sodium is 2 electrons in the first energy level (written as 2), 8 electrons in the second energy level (written as 8), and 1 electron in the third energy level (written as 1).

J.J. Thomson proposed the model of an atom in 1903, which helped in the understanding of electrons and protons. His model, known as the "plum pudding model," suggested that atoms were made up of a positively charged mass with negatively charged electrons embedded within it. This model was based on Thomson's discovery of electrons and his experiments with cathode rays. Thomson's work laid the foundation for further discoveries about the structure of the atom, leading to the later experiments conducted by Ernest Rutherford and his colleagues.

The present concept of the structure of an atom is given by Niels Bohr, not Goldstein. Niels Bohr proposed the Bohr model of the atom in 1913, which described electrons orbiting around a central nucleus in discrete energy levels or shells. This model accounted for the stability of atoms and explained phenomena such as the emission and absorption of light. On the other hand, Goldstein's contributions to atomic theory were related to the discovery of the proton and the canal rays, but his work did not provide the current understanding of the structure of an atom. Therefore, the correct answer is C: Niels Bohr.

Rutherford's Model is the model that does not explain the stability of an atom. Rutherford's model was proposed in 1911 and described the atom as a small, dense, positively charged nucleus surrounded by orbiting electrons. However, this model failed to explain why the negatively charged electrons did not simply fall into the positively charged nucleus due to the attractive electrostatic force between them. It was later modified by Niels Bohr with his Bohr's Model, which introduced the concept of quantized energy levels and explained the stability of atoms.

Thomson conducted a series of experiments in which he used a cathode ray tube to study 'cathode rays'. He discovered that these rays were composed of negatively charged particles, which were later named electrons. His work marked the discovery of the first subatomic particle, revolutionizing the study of atomic structure.

Bohr’s model describes that there is no change in the energy of electrons as long as they keep revolving in the same energy level and atoms remain stable. This model was proposed by Niels Bohr in 1913. According to his model, electrons revolve in certain stable orbits around the nucleus without the emission of radiant energy. These orbits or shells are associated with definite energies and are also called energy levels. Hence, as long as an electron remains in the same energy level, its energy remains constant and the atom remains stable.