Why is the average atomic mass for an element typically not a whole number?

Answer 1

Because of the existence of isotopes.

An element is defined by it atomic number, #Z#, the number of massive, positively charge particles (protons): #Z=1, H; Z=2, He; Z=3, Li...........Z=92, U#.
On the other hand, a given nucleus may contain different numbers of neutrons, massive, neutrally charged nuclear charges. If we take #C# as our exemplar, it is a fact that all carbon nuclei have 6 protons; #Z=6# by definition. Most carbon nuclei contain 6 neutrons, to give the #""^12C# isotope. A few carbon nuclei contain 7 neutrons, to give the #""^13C# isotope, which is a very important isotope as it allows #""^13C# #NMR" Spectroscopy"#. A smaller few contain 8 neutrons to give the #""^14C# isotope.
Now all these isotopes have 6 protons, but the different number of neutrons gives rise to different elemental masses. The weighted average of the individual isotopes is the quoted atomic mass, which for #C# is #"12.011 amu"#.

Transition metals typically have a range of isotopes, and thus non-integral atomic masses.

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Answer 2

Isotopes are atoms of the same element with different numbers of neutrons, which can cause variations in atomic mass. The average atomic mass for an element is usually not a whole number because it is a weighted average of the masses of all the naturally occurring isotopes of that element, taking into account their relative abundances.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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