The number of protons in an atom of an element is its atomic number. For example, the atomic number of sodium is 11. Every sodium atom has 11 protons and 11 electrons. It has 11 positive charges and 11 negative charges. The atomic number of an element or isotope cannot change, so you can use the atomic number to help figure out other characteristics, such as the number of electrons and neutrons in an atom.The atomic number is usually in the top left or top right corner of the element’s box, but it could be in a different spot. This is always a whole number.