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Why does changing the number of neutrons not change an atom into a different element?

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What are isotopes and how do they work? — isotope An overview of isotopes.

Changing the number of neutrons in an atom does not change its identity as a specific element because the identity of an element is determined solely by the number of protons in its nucleus, a value known as the atomic number.123

The chemical characteristics of an element are governed by the number and arrangement of its electrons. In a neutral atom, the number of electrons is equal to the number of protons. Because neutrons are electrically neutral, adding or removing them does not alter the atom's positive charge or its electron configuration, meaning the atom's chemical behavior remains nearly identical.1243

Atoms that have the same number of protons but different numbers of neutrons are called isotopes. While isotopes of the same element share the same position in the periodic table and exhibit similar chemical properties, they differ in their atomic mass and certain physical properties due to the change in the total number of nucleons.43