How did Dalton Atomic Theory explain the law of definite proportions?

1 Answer
Apr 26, 2014

Dalton's atomic theory consisted of several postulates.


  • All matter consists of indivisible particles called atoms.

  • Atoms of the same element are similar in shape and mass, but differ from the atoms of other elements.

  • Atoms cannot be created or destroyed.

  • Atoms of different elements may combine with each other in a fixed, simple, whole number ratio to form compound atoms.

  • Atoms of same element can combine in more than one ratio to form two or more compounds.

  • Atoms are the smallest unit of matter that can take part in a chemical reaction.

The law of definite proportions states that a chemical compound always contains exactly the same proportion of elements by mass.

For example, all samples of the compound carbon monoxide contain 42.88 % carbon and 57.12 % oxygen by mass.

The atomic theory explains the law of definite proportions:

Dalton proposed that the smallest particle of carbon monoxide was a molecule. This molecule consisted of one carbon atom and one oxygen atom.

If all oxygen atoms had a mass about 1.33 times that of carbon atoms, carbon monoxide would have exactly the above composition.