How do neutrons create different isotopes of the same element?

An element is defined by its atomic number, which is the number of protons in its nucleus. While all atoms of a specific element must have the same number of protons, they do not need to have the same number of neutrons.123

Isotopes are created when atoms of the same element possess different numbers of neutrons in their nuclei. Because neutrons contribute to the mass of an atom but do not change its electric charge or the number of electrons surrounding the nucleus, isotopes of the same element exhibit nearly identical chemical properties. However, because they contain different numbers of neutrons, these isotopes have different atomic masses and mass numbers.412

For example, hydrogen has an atomic number of 1, meaning every hydrogen atom has one proton. Its isotopes are distinguished by their neutron count: one isotope has no neutrons, another has one, and a third has two.1