Elements that have the same number of protons are called isoprotonic.
In essence, "isoprotonic" describes elements characterized by an identical quantity of protons within their atomic nuclei. The number of protons is the defining characteristic of an element, determining its atomic number and thus its chemical identity. Therefore, isoprotonic elements are essentially the same element, though they might differ in neutron number (leading to different isotopes).
While the term "isoprotonic" could be used to describe elements with the same number of protons, it's important to understand that the proper and universally accepted term is simply the same element. Isotopes are the term used to describe variants of that element that differ only in the number of neutrons.
For example, all carbon atoms have 6 protons. Carbon-12, Carbon-13, and Carbon-14 are all isoprotonic (all have 6 protons) and therefore all are carbon, but they are different isotopes of carbon.
In summary, the term "isoprotonic" refers to elements sharing the same number of protons; however, a more accurate description would be using the same element, with the differing forms being labeled as isotopes.
