Ma'anar ƙamus na "atomic number 15" yana nufin sinadari mai protons 15 a cikin tsakiya, wanda aka sani da phosphorus (alama: P) a cikin tebur na lokaci-lokaci. Lambar atomic na wani sinadari shine mai ganowa na musamman wanda ke wakiltar adadin protons a cikin tsakiya na zarra na wannan sinadari. Dangane da sinadarin phosphorus, yana da lambar atomic lamba 15, wanda ke nufin yana da protons 15 da electrons 15 a cikin yanayinsa na tsaka tsaki.