Class 9 Science — Chapter 3: ATOMS AND MOLECULES

What you'll learn

• ▸Law of Conservation of Mass
• ▸Law of Constant Proportions
• ▸Dalton's Atomic Theory
• ▸The Concept of an Atom
• ▸Chemical Symbols of Elements
• ▸Early Ideas of the Atom

Chapter Summary

--- PAGE 1 --- 0964CH03 Chapter 3 ATOMS AND MOLECULES Ancient Indian and Greek philosophers have always wondered about the unknown and unseen form of matter. The idea of divisibility of matter was considered long back in India, around 500 BC. An Indian philosopher Maharishi Kanad, postulated that if we go on dividing matter (padarth), we shall get smaller and smaller particles. Ultimately, a stage will come when we shall come across the smallest particles beyond which further division will not be possible. He named these particles Parmanu. Another Indian philosopher, Pakudha Katyayama, elaborated this doctrine and said that these particles normally exist in a combined form which gives us various forms of matter. Around the same era, ancient Greek philosophers – Democritus and Leucippus suggested that if we go on dividing matter, a stage will come when particles obtained cannot be divided further. Democritus called these indivisible particles atoms (meaning indivisible). All this was…

Practice Questions from this Chapter

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1. Describe atoms' secret world. Get Solution →
2. Explain chemical reactions simply. Get Solution →
3. Illustrate constant proportion examples. Get Solution →
4. Who laid the foundation of chemical sciences by establishing the two important laws of chemical combination? Get Solution →
5. What did the ancient Greek philosopher Democritus call the smallest indivisible particles of matter? Get Solution →
6. What is the modern standard reference used for measuring atomic masses? Get Solution →
7. The law stating that 'in a chemical substance the elements are always present in definite proportions by mass' is known as: Get Solution →
8. According to modern IUPAC conventions, what is the correct chemical symbol for Potassium? Get Solution →

Did you know?

• 💡 All the atoms in your body are billions of years old, born in exploding stars.
• 💡 If an atom were the size of a stadium, its nucleus would be a tiny pea.
• 💡 Diamonds and graphite are both made from only carbon atoms, yet look different.
• 💡 There are more atoms in a single breath than breaths in Earth's atmosphere.
• 💡 The Law of Conservation of Mass was first described by a French noble.

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