Proton
A positively charged particle that, together with neutrons, makes up the atomic nucleus. The nucleus of hydrogen is a single proton. The number of protons decides which element an atom is.
In 1919 Ernest Rutherford found that bombarding nitrogen with alpha particles knocks out hydrogen nuclei[1]. The result showed that the hydrogen nucleus is also a building block of other nuclei, and he later named the particle the proton.
A proton is about 1,836 times as heavy as an electron and carries a charge of the same size but opposite sign. The number of protons in the nucleus, the atomic number, decides whether an atom is hydrogen, carbon or uranium. Protons, all positive, repel one another; the nucleus holds together because a stronger force acts between protons and neutrons.
Related terms
- NeutronA particle with no electric charge that, together with protons, makes up the atomic nucleus. It weighs almost the same as a proton.
- Atomic nucleusThe tiny, heavy core at the centre of an atom, made of protons and neutrons and carrying a positive charge.
- Alpha particleA heavy, positively charged particle made of two protons and two neutrons: the same thing as a helium nucleus. It is thrown out by radioactive substances.