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Atoms and Molecules

Tamil Nadu Board · Class 10 · Science

Quick revision notes for Atoms and Molecules — Tamil Nadu Board Class 10 Science. Key concepts, formulas, and definitions for last-minute revision.

44 questions36 flashcards5 concepts

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Key Topics to Revise

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.
3

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.
4

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.

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Full Notes

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

Frequently Asked Questions

What are the important topics in Atoms and Molecules for Tamil Nadu Board Class 10 Science?
Key topics in Atoms and Molecules include Atoms and Molecules – Complete Chapter Overview, Mind map showing all major applications of Avogadro's law in chemistry, Summary of key formulas organized by category: atomic, molecular, and mole formulas. These are the concepts Tamil Nadu Board Class 10 examiners draw on most — study them first, then practise related questions.
How to score full marks in Atoms and Molecules — Tamil Nadu Board Class 10 Science?
Understand the core concepts first, then work through the 44 practice questions available for this chapter. Revise formulas and definitions regularly, and use flashcards for quick recall before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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All 10 chapters — Tamil Nadu Board Class 10 Science Revision Notes

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