One neutral atom of iodine has 53 electrons. The number of electrons in a neutral atom corresponds to the atomic number of the element.
The 53 electrons in iodine occupy five different energy levels. There are two electrons in the first level, eight in the second level, 18 in the third level, 18 in the fourth level and seven in the fifth level.
If iodine gains one electron, it becomes a negatively charged ion. The ion has a negative charge because it has 54 negatively charged electrons and 53 positively charged protons. When the number of protons in an atom does not equal the number of electrons in the atom, the atom takes on the charge of the most abundant subatomic particle. In this case, there is one more electron than proton, giving the ion a charge of +1.