Atoms of the same element have an equal number of what?

Atoms of the same element are defined by their atomic number, which represents the number of protons found in the nucleus of each atom. Since each element in the periodic table is uniquely identified by this number, all atoms of that element must have the same number of protons. This uniformity in proton number is essential to maintaining the chemical properties that define the element.

While it is true that atoms of the same element can have different numbers of neutrons (leading to the formation of isotopes), the number of protons remains constant for any given element. Similarly, the number of electrons in a neutral atom matches the number of protons; however, ions of an element can have varying electron counts. The term "nuclei" is more applicable to the entire atomic structure and does not relate specifically to the defining characteristic of an element. Thus, the correct understanding of atomic identity hinges on the constancy of proton numbers across all atoms of the same element.