Every atom has a tiny centre called the nucleus. The nucleus holds protons (positive charge) and neutrons (no charge). Around it move electrons (negative charge).
The number that names the element
The number of protons is the atomic number, and it decides the element:
| Protons | Element |
|---|---|
| 1 | Hydrogen |
| 6 | Carbon |
| 8 | Oxygen |
| 26 | Iron |
| 79 | Gold |
Add one proton to an atom and it becomes a different element.
Small but heavy
A proton is about 1,836 times heavier than an electron. So almost all the mass of an atom, and of you, sits in nuclei that are about 100,000 times smaller than the atom itself.
Made of smaller pieces
A proton is not a solid ball. It is made of three quarks (two "up" quarks and one "down" quark) held together by particles called gluons, through the strong force, the strongest force in nature at that tiny scale.
Why don't protons fly apart?
Protons all have positive charge, so they push each other away. Inside the nucleus, the strong force is stronger than that push, and it holds the nucleus together. In the Sun, hydrogen nuclei (single protons) are squeezed together so hard that they fuse into helium, and that is where sunlight comes from.