Lambar atomic ita ce adadin protons a cikin tsakiya na zarra. Yana da mahimmancin gano nau'in sinadari kuma yana ƙayyade wurinsa a cikin tebur na lokaci-lokaci. Lambar atomic tana wakiltar alamar "Z" kuma yawanci tana sama ko zuwa hagu na alamar kashi. Misali, adadin atomic na carbon shine 6, wanda ke nufin cewa tsakiya ya ƙunshi protons 6.
