Because the positive and negative charges cancel out, and you are left with only neutral charges.
An atom has three different subatomic particles:
- Proton - positive charge
- Neutron - neutral charge
- Electron - negative charge
The protons and neutrons live in the nucleus of an atom (its center), and contain most of the atom's mass. The electrons 'orbit' the nucleus in shells, or energy levels.
In a neutral atom, the number of protons = the number of electrons.
You can't change the number of protons in the atom of and element without changing that element. If you change the number of neutrons, you have something called an isotope. When you change the number of electrons you have an ion. This positive/negative relationship is seen in the ion charges of atoms.
When it loses one electron, it becomes
Since there is one more positive charge than negative charge (i.e. the sum of positive