Chapter 7 of 10
Syllabus
Atoms and Molecules — Syllabus
Tamil Nadu Board · Class 10 · Science
What Atoms and Molecules covers in Tamil Nadu Board Class 10 Science: 4 topics, for the 2026-27 session. Topics include Modern Atomic Theory – Key.
44 questions36 flashcards5 concepts
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4 Topics · Tamil Nadu Board Class 10 Science · 2026-27
Topics in Atoms and Molecules
1
1. Modern Atomic Theory – Key Postulates
- The original Dalton's atomic theory had several limitations that were corrected by later discoveries, leading to the Modern Atomic Theory.
- An atom is NO longer indivisible — it contains subatomic particles: protons, neutrons, and electrons.
- Atoms of the SAME element can have DIFFERENT atomic masses — these are called ISOTOPES (e.g., Cl-35 and Cl-37, both have atomic number 17).
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2. Atom and Atomic Mass
- The mass of an atom is mainly due to protons and neutrons (electrons have negligible mass).
- Mass number = Number of protons + Number of neutrons.
- Atomic mass is measured in atomic mass units (amu), also written as 'U' (unified atomic mass unit) in the modern system.
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3. Molecules, Molecular Mass, and Atomicity
- A molecule is a combination of two or more atoms held together by chemical bonds.
- Most atoms (except noble gases) exist in the combined form as molecules.
- Atomicity = the number of atoms present in one molecule of an element or compound.
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4. Mole Concept
- The mole (mol) is the SI unit for the amount of a substance.
- 1 mole of any substance contains exactly 6.023 × 10²³ entities (atoms, molecules, ions, etc.).
- This number (6.023 × 10²³) is called Avogadro's Number (Nₐ), named after Amedeo Avogadro.
Key Concepts
An atom is the smallest particleRelative Atomic Mass is the ratioA molecule is a combinationRelative Molecular Mass is the sumThe mole is a unit
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What are the important topics in Atoms and Molecules for Tamil Nadu Board Class 10 Science?
Key topics in Atoms and Molecules include Modern Atomic Theory – Key Postulates, Atom and Atomic Mass, Molecules, Molecular Mass, and Atomicity, Mole Concept. Study these first, then practise questions on each for the Tamil Nadu Board Class 10 board exam.
How should I revise Atoms and Molecules for the Tamil Nadu Board Class 10 board exam?
Learn the core ideas first, then work through the 44 practice questions on Atoms and Molecules. Revise definitions regularly and use flashcards for quick recall before the exam.
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Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.
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