One neutral atom of sodium has 11 electrons. A sodium ion has 10 electrons.
Electrons are negatively charged particles located outside the nucleus of an atom. On the Periodic Table of the Elements, sodium has an atomic number of 11. This means a neutral sodium atom has 11 electrons and 11 protons, which are particles with positive charges. In a neutral atom, the number of protons equals the number of electrons, giving the atom a net charge of zero.
Some atoms become ions by giving up or gaining electrons. Sodium becomes an ion by losing one electron. This leaves the atom with 11 positively charged protons and 10 negatively charged electrons, giving the sodium ion a net charge of +1.