which part of an element determines its atomic number?
Isotopes ï¯ Isotopes ï¯ Isotopes are atoms of the same element that have different numbers of neutrons in the nucleus. Remember that it is only the number of protons that determines the identity of an element. ï¯ Let's look at the simplest element, hydrogen. The common variety of hydrogen has a single proton in the nucleus and a single electron in an orbital surrounding the nucleus.