Definition that contains atomic number
- isotope one of two or more atoms with the same atomic number but with different numbers of neutrons
- actinon any of a series of radioactive elements with atomic numbers 89 through 103
- transactinide any of the artificially produced elements with atomic numbers greater than 103
- lanthanide series the rare-earth elements with atomic numbers 57 through 71; having properties similar to lanthanum
- actinide any of a series of radioactive elements with atomic numbers 89 through 103
- rare earth any element of the lanthanide series (atomic numbers 57 through 71)
- mendeleev's law (chemistry) the principle that chemical properties of the elements are periodic functions of their atomic numbers
- transactinide of or belonging to the elements with atomic numbers greater than 103
- lanthanoid any element of the lanthanide series (atomic numbers 57 through 71)
- actinoid any of a series of radioactive elements with atomic numbers 89 through 103