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Structure of the Atom — Question 7

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Question 7

Define valency by taking examples of silicon and oxygen.

Answer

The definite combining capacity of the atoms of each element, wherein electrons are lost, gained or shared to make the octet of electrons present in the outermost shell, is defined as valency.

(i) The electronic configuration of silicon [14] is 2, 8, 4. It has 4 electrons in its outermost shell. So, the valency of silicon = 8 – the number of electrons in the outermost shell = 8 - 4 = 4.

Hence, valency of silicon = 4.

(ii) The electronic configuration of oxygen [8] is 2, 6. It has 6 (more than 4) electrons in its outermost shell. So, the valency of oxygen = 8 – the number of electrons in the outermost shell = 8 − 6 = 2.

Hence, valency of oxygen = 2.

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Science | Chapter 4: Structure of the AtomWeb Content — Quick Reference

Chapter 4: Structure of the Atom — Quick Reference

Thomson model Rutherford experiment Bohr model electron proton neutron isotopes isobars electronic configuration

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⁻
Exam Tips for Chapter 4
  • 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.
Related Resources
  • 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
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