Definition that contains atomic number
- isotope one of two or more atoms with the same atomic number but with different numbers of neutrons
- 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
- rare-earth element any element of the lanthanide series (atomic numbers 57 through 71)
- periodic law (chemistry) the principle that chemical properties of the elements are periodic functions of their atomic numbers
- lanthanide any element of the lanthanide series (atomic numbers 57 through 71)
- transuranic element any element having an atomic number greater than 92 (which is the atomic number of uranium); all are radioactive
- lanthanon any element of the lanthanide series (atomic numbers 57 through 71)
- actinide series (chemistry) a series of 15 radioactive elements with increasing atomic numbers from actinium to lawrencium