How do isotopes of an element differ? In what ways are they the same?

1 Answer
anor277
Dec 17, 2016

Isotopes differ in the number of neutrons, fundamental, massive, neutral nuclear particles, their atoms contain.

Explanation:

Let's take the element hydrogen as an exemplar, which so far as I know is the most abundant element in the universe. Most hydrogen nuclei are #""^(1)H#; their nuclei each contain just the one proton, just the one fundamental, massive, positively-charged nuclear particle - we would call this nucleus the #"protium isotope"#.

A few hydrogen atoms, are substituted by an extra massive nuclear particle, the neutron, which we would represent as #""^2H#, #"the deuterium isotope"#. Note that the element is still hydrogen, because #Z#, #"the atomic number"#, is still #1#. And a smaller few hydrogen nuclei are substituted by a nuclide with 2 neutrons, i.e. #""^3H#, #"the tritium isotope"#.

And thus all isotopes of the same element necessarily contain #"THE SAME NUMBER OF PROTONS,"# but #"DIFFERENT NUMBERS OF NEUTRONS"#. Most elements have several different isotopes, and their weighted average gives rise to the quoted atomic mass. Capisce?

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