Atomic number
From Tardis Wiki, the free Doctor Who reference
Atomic number was a property of elements on the periodic table.
According to the Eighth Doctor, the atomic number of beryllium was 4. (PROSE: The Deadstone Memorial)
Zoe Heriot started saying the the atomic number of tellurium was 50 but cut herself off when she saw a Kroton. (TV: The Krotons)
According to the Thirteenth Doctor, the atomic number of antimony was 51. (TV: The Tsuranga Conundrum)
According to the Twelfth Doctor, the atomic number of caesium was 55. (TV: Flatline)
