An atom contains of three different sorts of [?] .
The [?] charged are called protons, the negative charged [?]
and the uncharged or [?] are known as neutrons.
Protons and neutrons are [?]. They build the atomic nucleus.
The elementary [?] (of a proton or an electron) is 1,6 . 10-19 As.
1 u = 1,67. 10-24 g is the mass value of a proton and known as atomic [?] .
Almost the entire mass of an atom is concentrated in the atomic [?]. .