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Atoms and Molecules — Revision Notes

NIOS · Class 10 · Science & Tech

Atoms and Molecules revision notes for NIOS Class 10 Science & Tech: 4 topics in quick points. Part of the NIOS Class 10 Science & Tech syllabus.

93 questions42 flashcards3 formulas & key relations5 concepts

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An infographic comparing the ancient Indian (Maharishi Kanad, Pakudha Katyayan) and Greek (Democritus, Leucippus) philosophical ideas about the divisibility of matter and the concept of 'Parmanu' and
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Key Topics to Revise

1

1. Laws of Chemical Combination

  • The law of conservation of mass states that in every chemical reaction, total mass of reactants is equal to total mass of products.
  • Lavoisier proved this law using a chemical balance in an experiment involving mercury and oxygen.
  • When mercury was heated in air, mercury (II) oxide formed and the gas left behind did not support combustion or life; it was nitrogen.
2

2. Dalton’s Atomic Theory and Atom

  • John Dalton arranged earlier atomic ideas into a scientific theory and published it in 1803.
  • Dalton's atomic theory explained the laws of conservation of mass and constant proportions.
  • Dalton’s first postulate states that matter consists of indivisible atoms.
3

3. Size, Mass, Atomic Number, and Isotopes

  • Atoms are extremely small and cannot be seen with the naked eye.
  • Nanometer is used to express atomic size, and 1 nm = 10^-9 m.
  • One teaspoon of water contains about three times as many atoms as the Atlantic ocean contains teaspoons of water.
4

4. Molecule, Molecular Mass, and Formula Mass

  • A molecule is the smallest particle of an element or compound that can exist freely under ordinary conditions.
  • A molecule is an aggregate of two or more atoms held together by chemical bonds.
  • Oxygen molecule O2 is diatomic.

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Full Notes

Key Concepts

Ancient Indian and Greek thinkers proposedIn a chemical reactionA pure compound always containsDalton arranged earlier atomic ideas intoWhen two elements form more than

Frequently Asked Questions

What are the important topics in Atoms and Molecules for NIOS Class 10 Science & Tech?
Key topics in Atoms and Molecules include Laws of Chemical Combination, Dalton’s Atomic Theory and Atom, Size, Mass, Atomic Number, and Isotopes, Molecule, Molecular Mass, and Formula Mass. Study these first, then practise questions on each for the NIOS Class 10 board exam.
How should I revise Atoms and Molecules for the NIOS Class 10 board exam?
Learn the core ideas first, then work through the 93 practice questions on Atoms and Molecules. Revise 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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