Protons and Neutrons: The Nucleus of Matter

Protons and neutrons sit at the heart of every atom, forming its nucleus.
Protons carry a positive electric charge, while neutrons are electrically neutral.
Both are made of quarks, bound tightly together by gluons and the strong nuclear force.
A proton is built from two up quarks and one down quark.
A neutron is built from two down quarks and one up quark.
The number of protons defines an element—one proton is hydrogen, six is carbon, 92 is uranium.
Neutrons act like a glue, helping stabilize the nucleus against proton–proton repulsion.
Free neutrons are unstable, decaying into a proton, electron, and neutrino in about 15 minutes.
The mass of protons and neutrons makes up nearly all the mass of ordinary matter.
Without protons and neutrons, atoms, molecules, and life itself could not exist.