Lesson 6 of 12 · 7 min
Dalton's atomic theory
NCERT § "Dalton's Atomic Theory"
Why should hydrogen and oxygen always meet 1 : 8 by mass, never 1 : 7 or 1 : 9? Dalton's answer was that both are made of tiny particles that cannot be cut.
The lesson in notes
In short
Dalton proposed that matter is made of indivisible atoms.
Every atom of one element is the same as every other, mass included, while atoms of two different elements have different masses.
A compound arises when atoms of two or more elements join in a set, unchanging ratio.
A reaction only reshuffles atoms into new partners; no atom is made or lost.
The theory explained the laws of conservation of mass, definite proportions and multiple proportions.
It could not explain the law of gaseous volumes, and it gave no reason why atoms combine at all.