John Dalton's atomic theory, which was proposed in the early 19th century, included five major points:
1. **Elements are composed of indivisible particles:** Dalton's theory suggested that all matter is made up of tiny, indivisible particles called atoms. These atoms are the fundamental building blocks of matter.
2. **All atoms of a given element are identical:** Dalton proposed that all atoms of the same element are identical in size, mass, and chemical properties. However, atoms of different elements have different properties.
3. **Atoms combine to form compounds:** According to Dalton, atoms combine in simple, whole-number ratios to form compounds. This means that the ratio of atoms in a chemical compound is always a small whole number.
4. **Chemical reactions involve the rearrangement of atoms:** Dalton's theory stated that chemical reactions are the result of the rearrangement of atoms. Atoms are neither created nor destroyed in chemical reactions; they are merely rearranged to form different compounds.
5. **Atoms are indivisible and indestructible:** Dalton believed that atoms are indivisible and indestructible. This means that atoms cannot be further divided into smaller particles, and they cannot be destroyed in chemical reactions; they can only be rearranged.
While Dalton's atomic theory laid the foundation for modern atomic theory, it has since been refined and expanded upon based on new discoveries in atomic and subatomic physics.