Atomic number 20
For example, all calcium atoms have an atomic number of 20 but there 
are... [DOC] [TLE] Atomic Weights and Isotopic Compositions for All Elements [PAR] ... Atomic Weight = 18.998403163(6) Notes = Atomic Number = 10 Atomic 
Symbol = Ne Mass Number = 20 Relative Atomic Mass = 19.9924401762(17) 
Isotopic... [DOC] [TLE] Calcium - Wikipedia [PAR] Calcium is a chemical element with symbol Ca and atomic number 20.