You are here
💡 One theory to explain both laws
Why is mass conserved, and why are proportions fixed? Dalton answered both with a single bold idea — atoms simply rearrange; they are never made or destroyed.
What are the main postulates of Dalton’s atomic theory?
- All matter is made of tiny particles called atoms .
- Atoms are indivisible — not created or destroyed in a reaction.
- Atoms of a given element are identical in mass and properties.
- Atoms of different elements differ in mass and properties.
- Atoms combine in simple whole-number ratios to form compounds.
👤 Meet a Scientist — John Dalton
- Born in England; moved to Manchester in 1793 to teach mathematics, physics and chemistry.
- Presented his atomic theory in 1808 , a turning point in the study of matter.
A postulate is a basic assumption accepted as true without formal proof, from which further ideas are developed. Dalton’s postulates explain why substances combine in fixed proportions and why mass is conserved — atoms merely rearrange.
⏸▶ Pause and Ponder
- 7. Assertion (A): 2 g of hydrogen combines with 16 g of oxygen to form 18 g of water. Reason (R): By Dalton’s theory, atoms combine in a simple whole-number ratio by mass. Answer: (i) Both A and R are true and R is the correct explanation of A.
Important Definitions
- Postulate — a basic assumption accepted as true without formal proof.
- Dalton’s Atomic Theory — a set of postulates explaining conservation of mass and fixed proportions using indivisible atoms.
