Question 1

Which subatomic particle was discovered by J.J. Thomson using the cathode ray tube experiment?

Accepted Answer

Electron. The electron was identified by J.J. Thomson through his work with cathode rays. This discovery proved that atoms contain negatively charged particles. He later proposed the 'Plum Pudding' model to describe atomic structure.

Question 2

What is the primary reason an atom is electrically neutral under normal conditions?

Accepted Answer

Equal number of protons and electrons. The positive charge of protons is exactly balanced by the negative charge of electrons. In a neutral atom, these two types of particles must be present in equal numbers. This balance ensures the net charge of the entire atom remains zero.

Question 3

Which component of the atom contains almost all of its mass but occupies very little space?

Accepted Answer

Nucleus. The nucleus houses the protons and neutrons which contribute nearly all atomic mass. It is located at the center and is extremely dense compared to the rest of the atom. Rutherford's gold foil experiment was instrumental in identifying this central core.

Question 4

What name is given to atoms of the same element that have different numbers of neutrons?

Accepted Answer

Isotopes. Isotopes are variants of a chemical element which differ in neutron count. They possess the same atomic number but different mass numbers. Most elements found in nature exist as a mixture of various isotopes.

Question 5

Which quantum number determines the primary energy level or shell of an electron?

Accepted Answer

Principal quantum number. The principal quantum number (n) defines the main energy level of an electron. It relates to the average distance of the electron from the nucleus. Higher values of 'n' indicate shells that are further away from the center.

Atomic Structure — Set 1