The electron is the lightest particle of the atom. It has a mass of 9.1 x 10-28 grams. Comparing this mass to that of the proton's at 1.6726 x 10-24 grams, an electron is nearly 0.0005 times the proton's mass.
The electrons has a negative charge, while the proton has a positive charge. The neutron has a mass of 1.6749 x 10-24 grams, while the atom's size is between 10-21 and 10-23 grams.
Atoms have the same number of electrons and protons. On the periodic table, the mass number of an element is found by adding the number of protons and the number of neutrons. However, isotopes of an element will have varying numbers of neutrons.