What are the main ideas of Dalton's atomic theory?

Answer 1

The ancient Greek philosophers had talked about atoms, but Dalton's theory was different in that it had the weight of careful chemical measurements behind it. It wasn't just a philosophical statement that there are atoms because there must be atoms. His atomic theory had these fundamental points :

• Elements consist of tiny particles called atoms.
• Elements are pure because all atoms of an element are identical and that in particular they have the same mass.
• Elements differ from one another because atoms of each element are different from one another; in particular, they have different masses.
• Compounds consist of atoms of different elements combined together. Compounds are pure substances (remember they cannot be separated into elements by phase changes) because the atoms of the different elements are bonded to one another somehow, perhaps by hooks, and are not easily separated from one another.
• Compounds have constant composition because they contain a fixed ratio of atoms and each atom has its own characteristic weight, thus fixing the weight ratio of one element to the other.
• Chemical reactions involved the rearrangement of combinations of the atoms in a substance.

Dalton's Atomic Theory had several main points, which are variously grouped into five statements :

1) All matter is made of atoms.

2) Atoms of a given element are identical in size, mass and chemical properties.

3) Atoms of different elements have different masses and properties.

4) Compounds are formed by a combination of two or more different kinds of atoms. The elements combine in simple, whole-number ratios.

5) Atoms cannot be subdivided, created, or destroyed, but merely rearranged in their compounds with other elements. They can be combined, separated, or changed in the way in which they are arranged.

Answer 2

Just like Democritus, Dalton proposed that atoms cannot be divided. According to Dalton, all atoms of a givin element were exactly alike.