Chemistry › Isotope
Mendeleev · Isotope
Helium-4
Helium-4: atomic number 2, mass number 4, with 2 protons and 2 neutrons.
IsotopeHe
42He
Protons2
Neutrons2
Electrons (neutral)2
The proton count fixes the element: 2 protons identify Helium. Mass number 4 is the total number of protons and neutrons.
A neutral Helium-4 atom also has 2 electrons. Changing neutrons changes the isotope; changing electrons changes the charge.