Deep inside every atom, nestled in the dense core called the nucleus, sit protons — particles carrying a positive electrical charge. The proton is one of nature's most important building blocks because its count determines what element an atom is. One proton makes hydrogen, six make carbon, 26 make iron, 79 make gold. It is that simple and that profound: the entire diversity of the chemical world comes down to how many protons are packed into a nucleus.
The proton was discovered through the pioneering work of Ernest Rutherford, who in 1917 conducted experiments bombarding nitrogen gas with alpha particles. He observed that hydrogen nuclei were knocked out of the nitrogen atoms, proving that the hydrogen nucleus (a single proton) was a fundamental component of all atomic nuclei. Rutherford named it the proton, from the Greek word "protos" meaning "first." Each proton has a mass of about 1.007 amu — roughly 1,836 times heavier than an electron — and carries a charge of +1.
Protons do something remarkable inside the nucleus: they stay together despite all carrying the same positive charge, which should make them repel each other violently. The force holding them together is called the strong nuclear force, the most powerful of nature's four fundamental forces. It operates only at incredibly short distances (within the nucleus) but overpowers the electromagnetic repulsion between protons. In very large nuclei with many protons — like uranium with 92 — this balancing act between repulsion and strong force becomes unstable, which is why heavy elements tend to be radioactive.