Proton

The plutonium-244 nucleus is the heavy atomic nucleus of a long-lived plutonium isotope, built from 94 protons and 150 neutrons. It was forged in rare neutron-rich explosions before the Solar System formed, and its 81.3-million-year half-life made it an important extinct radionuclide in early Solar System history.

Object class

Atomic nucleus

Composition

94 protons, 150 neutrons

The electron is the fundamental particle that gives atoms their chemistry and matter its electric currents. Experiments show no evidence of any internal structure, so its size is represented here by an upper bound rather than a measured diameter.

Object class

Lepton

Hydrogen is the universe’s simplest and most common atom. Most hydrogen nuclei were forged in the first minutes after the Big Bang, and neutral hydrogen atoms emerged only after the universe cooled enough for electrons and protons to combine about 380,000 years later.

Object class

Atom

Composition

1 proton, 1 electron