Constituents of
the Atom
Atoms are composed of three classes of constituents, as illustrated in the following table.
Constituent
Symbol
Charge
Mass
Electrons
e
-
-1
9.1 x 10
-28
g
Protons
p
+
+1
1836 x electron mass
Neutrons
n
0
Approximately that of p
+
Thus, most of the mass of atoms resides in the neutrons and protons which occupy the dense central region called the
nucleus
.