Neutral atoms do not have a charge indicated on them because they have an equal number of protons and electrons, which cancel each other out. This means that the net electrical charge of a neutral atom is zero.
Protons and neutrons, which make up the nucleus of an atom, are positively charged. Electrons, which orbit the nucleus, are negatively charged. In a neutral atom, the number of protons and electrons is equal, so the positive charge of the protons is canceled out by the negative charge of the electrons, resulting in a net charge of zero.
However, atoms can gain or lose electrons to form ions, which do have a net electrical charge. If an atom gains one or more electrons, it becomes negatively charged and is called an anion. If an atom loses one or more electrons, it becomes positively charged and is called a cation. The charge of an ion is indicated by a superscript after the chemical symbol for the element, for example, Cl- for chloride ions (anions) and Na+ for sodium ions (cations).