Different scientists investigated the structure of the atom after Rutherford's new model was put forward. By the 1930s they had found that:
An atom has a central nucleus. This is surrounded by electrons arranged in shells.
The nucleus is very small compared to the atom as a whole:
Atoms are too small to be seen clearly, even with very powerful microscopes:
The nucleus of the simplest atom - hydrogen - contains only one proton and no neutrons.
The masses of subatomic particles are very tiny. Instead of writing their actual masses in kilograms, we often use their relative masses. The relative mass of a proton is 1, and a particle with a relative mass smaller than 1 has less mass.
|Subatomic particle||Relative mass||Relative charge|
The mass of an electron is very small compared to a proton or a neutron. Since the nucleus contains protons and neutrons, most of the mass of an atom is concentrated in its nucleus.
Protons and electrons have electrical charges that are equal and opposite.