Introduction of The atom

An atom is the smallest particle of an element that has all the chemical properties of that element.

Dalton's atomic theory

Dalton's atomic theory contains the following main ideas:

1. Matter is made up of small, indivisible particles called atoms.
2. Atoms of the same element are all exactly alike in every way and have definite weights.
3. Atoms are indestructible and they cannot be created.
4. Atoms of different elements have different weights and possess different properties.
5. Atoms of different elements combine in small whole numbers to form ‗compound atoms.

The shortcomings of Dalton's atomic theory

1. It not explain the structure of the atom. He could not explain how elements differ from each other.
2. It did not explain why atoms combine with each other
3. It did not explain the forces that bind atoms together in a molecule

Modifications to Dalton's atomic theory

1. Atoms can be created, destroyed, or split during nuclear reactions (e.g., uranium-235 splits in nuclear fission).
2. Some elements have isotopes – atoms of the same element with different masses (e.g., carbon-12, carbon-13, carbon-14).
3. Atoms are made of smaller particles – protons, neutrons, and electrons.
4. Atoms can combine in different ratios to form different compounds (e.g., CO and CO₂).