* Protons determine the element: The number of protons in an atom's nucleus defines what element it is. An atom with 12 protons is always a Magnesium (Mg) atom.
* Neutrons determine isotopes: The number of neutrons can vary within an element, creating different isotopes. An atom with 12 protons and 12 neutrons is a common isotope of Magnesium, while an atom with 12 protons and 16 neutrons is a different isotope of Magnesium.
Therefore, both atoms are Magnesium (Mg) but they are different isotopes of Magnesium.
