Because in a neutral atom, there are an equal number of positive protons and negative electrons. The equal number causes the charges to cancel out, making the net charge 0.
There is a neutral charge on an atom when the number of protons is equal to the number of electrons. This is most common in the Noble gases, such as Neon (atomic number 10, the second Noble Gas),...
Not all atoms have zero electrical charge, but most do because they have the same numbers of protons and neutrons. The net charge, or total charge of such an atom is zero. It is electrically neutral....
It is NOT always zero. If the charge is not zero, it is called an ion. However, atoms often tend to neutralize their charges; this is related to the electric forces. (If there is an excess electron...