Question 14
For the following statements, write T for True and F for False.
(a) J.J. Thomson proposed that the nucleus of an atom contains only nucleons.
(b) A neutron is formed by an electron and a proton combining together. Therefore, it is neutral.
(c) The mass of an electron is about times that of a proton.
(d) An isotope of iodine is used for making tincture iodine, which is used as a medicine.
(a) False.
Reason — Thomson proposed that:
- An atom consists of a positively charged sphere and the electrons are embedded in it.
- The negative and positive charges are equal in magnitude. So, the atom as a whole is electrically neutral.
(b) False.
Reason — Neutron is not formed by an electron and a proton combining together. It is present in the nucleus of an atom alongside protons.
(c) True.
Reason — The mass of an electron is about times that of a proton.
(d) False.
Reason — Tincture iodine is an antiseptic that usually contains 2-7% elemental I-127 dissolved in a mixture of ethanol and water. Normal iodine is used in its preparation, not its isotope.
Chapter 4: Structure of the Atom — Quick Reference
Quick Revision Points
- Thomson: positive sphere with embedded electrons (plum pudding)
- Rutherford: nucleus (dense, positive) + electrons in orbits. Limitation: electron should spiral in
- Bohr: electrons in fixed energy levels (shells K, L, M, N)
- Max electrons per shell: 2n² (K=2, L=8, M=18, N=32); outermost max 8
- Z = protons = electrons; A = protons + neutrons; neutrons = A − Z
- Isotopes: same Z, different A. Isobars: different Z, same A
- Valency: ≤ 4 → valency = outermost e⁻; > 4 → valency = 8 − outermost e⁻
- Read the detailed chapter notes for complete coverage of all NCERT topics.
- Practice all NCERT in-text and back exercise questions — they are frequently asked in exams.
- Focus on comparison tables, diagrams, and definitions — these are high-scoring areas.
- For numericals (if applicable), practice at least 20 problems of varying difficulty.
- Refer to the practice question bank (200+ questions) for thorough preparation.
- Detailed Notes: ch04-structure-of-the-atom.html
- Practice Questions: 100+ questions with answers in 05-practice-questions/
- Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
- Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html