Why does an atom have no overall charge?

An atom has no overall charge because each element has the same number of protons and electrons. Protons have a +1 charge, and electrons have a -1 charge, these charges cancel out if there is the same amount of each. For example, carbon has 6 protons, we know this because the atomic number (lower number on the periodic table) for carbon is 6. These 6 protons add up to a +6 charge, but carbon also has 6 electrons too, which supply a -6 charge, leading to no overall charge.