mass number
Protons plus neutrons
Mass number is the total count of protons and neutrons in an atomic nucleus.
It appears as a superscript before an element's symbol: ¹⁴C (carbon-14) has a mass number of 14.
Unlike atomic number, which identifies the element, mass number distinguishes isotopes—atoms of the same element with different neutron counts.
Elemental variant by mass
- radioisotopeUnstable atomic nucleus variant
- nuclideAtom classified by nucleus
- carbon-12Stable carbon isotope
- carbon-14Radioactive isotope for dating
uranium-235 · uranium-238 · deuterium · tritium · radioactive decay · half-life · isobar · isomer
Positive nuclear particles
- neutronsUncharged subatomic particles
- nucleusCentral controlling part
- nuclideAtom classified by nucleus
- superscriptRaised typographical character
Protons or neutrons
- baryonsThree-quark subatomic particles
- protonsPositive nuclear particles
- neutronsUncharged subatomic particles
- quarksFundamental hadron components
hadrons · fermions · subatomic particles · particle physics · elementary particles · gluons
Dense atomic center
- nuclear reactionAtoms changing their cores
- fissionNuclear breakup releasing energy
- fusionJoining into unity
- nucleosynthesisAtomic core formation process
strong force · nuclear physics · radioactivity · alpha particle · beta decay · gamma radiation · chain reaction · nuclear energy
isotope
Elemental variant by mass
- radioisotopeUnstable atomic nucleus variant
- nuclideAtom classified by nucleus
- carbon-12Stable carbon isotope
carbon-14 · uranium-235 · uranium-238 · deuterium · tritium · radioactive decay · half-life · isobar · isomer
protons
Positive nuclear particles
nucleons
Protons or neutrons
- baryonsThree-quark subatomic particles
- protonsPositive nuclear particles
- neutronsUncharged subatomic particles
quarks · hadrons · fermions · subatomic particles · particle physics · elementary particles · gluons
atomic nucleus
Dense atomic center
- nuclear reactionAtoms changing their cores
- fissionNuclear breakup releasing energy
- fusionJoining into unity
nucleosynthesis · strong force · nuclear physics · radioactivity · alpha particle · beta decay · gamma radiation · chain reaction · nuclear energy
atomic weight
Element's average isotope mass
- moleSubterranean insectivore
- math & science termspi, infinity, zero, billion, million
- atomic physicsatom, atoms, atomic nucleus, electron, neutron
- atomic scienceatom, electron, proton, neutron, nucleus
- nuclear sciencenuclear fission, nuclear physics, nuclear fusion, radiation, nuclear fuel
- element propertiesatomic weight, symbol, electronegativity, melting point, boiling point
- massmasses, bulk, biomass, matter, substance
mass, number, massive, masonry, massif, masseur, masseuse, masseter