Components of Atomic Structure
The chart below lists the basic particles of the atom.
| Particle | Charge | Actual Mass | Relative Mass to Proton | Discovery |
| Electron | - (e-) | 9.109 x 10-28 g | 1/1837 | J.J. Thompson - 1897 |
| Proton | + (p+) | 1.673 x 10-24g | 1 | ----------early 1900's |
| Neutron | 0 (no) | 1.675 x 10-24 g | 1 | J.C. Chadwick - 1932 |
Atomic weight is the mass of an atom expressed relative to a particular atom of Carbon being 12 mass units. The number of protons and neutrons in the nucleus is called the mass number and corresponds to the atomic weight rounded off to the nearest whole number. The atomic number is the number of protons in the nucleus.
If atoms of the same element with identical atomic numbers have different masses, they are called isotopes.