All matter is made up of atoms, and all atoms are made up of 3 subatomic particles.
- The proton, a positively charged and heavy particle
- The neutron, a neutrally charged particle with the same mass as that of the proton
- The electron, a negatively charged and very light particle
All atoms are structurally similar:
- The protons and neutrons are clumped together in a dense, positively charged nucleus. (only hydrogen atoms are different, as it has only one proton in the nucleus)
- The electrons orbit the dense nucleus.
The current model of the atom is proven with Rutherford’s gold-foil scattering experiment:
- Alpha particles (helium nuclei, consisting of 2 protons and 2 neutrons each) are fired at a thin sheet of gold foil.
- Most of the alpha particles pass through the foil without any deflection, indicating that the atom is mostly empty space.
- Some alpha particles get deflected at various angles, sometimes completely deflecting back to the source. This shows that the atom has a small and dense nucleus capable of deflecting the alpha particles completely.

5.01 - Atomic Model

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