Dalton created the atomic theory in 1803, which states:
1. All matter is made of small particles called atoms.
2. Atoms are indivisible. During a chemical reaction, atoms can be rearranged. However, they are never created nor distroyed.
3. All atoms of a given element are identicle in mass and size.
4. Atoms of different elements differ in mass and size.
5. A compound always contains the same ratio of the atoms that make it.
6. An atom is the smallest particle of an element.
Dalton's theory became widely accepted because it was based on quantitative experimental data, rather than pure qualitative observations.
Point number two of his theory above accounts for chemical reactions and the creation of compounds and hints towards the law of constant proportions. Point two also hints towards the law of conservation of mass.
Most of Dalton's ideas withstood the test of time, even as new data was derived. However, the following points had to be slightly altered:
- Atoms are made of subatomic particles (protons, electrons, and neutrons).
- The concept of isotopes: not all atoms of the same element have the same mass.
- Atoms may undergo nuclear fusion and decompose.