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What is the average mass of an element's naturally occurring atom or isotopes?
Below are the 3 naturally occurring isotopes of Oxygen and their % Natural abundance.
Now multiply and find the average atomic weight of Oxygen
O-16 (15.99491463 * .99757) = 15.95605
O-17 (16.9991312 * 0.00038) = 0.00646 O-18 17.9991603 * 0.00205) = 0.036898
Sum =15.95605 + 0.00646 + 0.036898 = 15.9994
My periodic table has the atomic mass of Oxygen as 15.999. Yee Haw!
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DevinThe average Atomic Mass of an element's naturally occurring atom isotope is calculated by taking the weighted average of the masses of its isotopes based on their abundance in nature. This value is listed on the Periodic Table for each element.
Approximately 20 elements such as yttrium and sodium have only one stable, naturally-occuring isotope. All remaining elements have at least two isotopes. The atomic mass of any stable element as shown in the periodic table is the weighted average of all of that element's stable, naturally-occuring isotopes. Thus, except for the elements that have only one stable, naturally-occuring isotope, none of a given element's isotopes have the atomic mass shown in the periodic table; each isotope has its own atomic mass.
What may be confusing to some students is the way all isotopes are named and the fact that no stable isotope has a whole number as its atomic weight - there is either some mass "missing" or some "extra" mass. Isotopes are denoted by "nuclide symbols." Let's look at chlorine (Cl) as an example: There are two natural and stable isotopes of Cl. The nuclide symbols are 35Cl and 37Cl, the respective atomic masses are 34.969 u and 36.966 u, where u stands for atomic mass unit, and the natural abundances of the isotopes are 75.76% and 24.24%. The weighted atomic mass for Cl is (34.969u x 0.7576) + (36.966u x 0.2424) = 35.45u. This is the atomic mass shown on the periodic table (to four significant figures). Clearly, both Cl isotopes appear to be missing some mass. The difference in mass between what is indicated by the nuclide symbol and the actual mass of the isotope is due to the fact that the isotope was formed from nuclear fission in a star. The tremendous amount of energy released in a nuclear fission reaction comes from mass being converted to energy per Einstein's equation E = MC2.
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What is a naturally occuring isotope?
A naturally occurring isotope is a form of an element with the same number of protons but a different number of neutrons in the nucleus. These isotopes are found in nature and contribute to the overall abundance of elements on Earth. An example is carbon-12, which is the most abundant carbon isotope in nature.
What is an isotope of 39K?
An isotope of 39K is potassium-39. It is a stable and naturally occurring isotope of potassium. It makes up about 93% of all naturally-occurring potassium.
What are all the elements that do not have isotopes?
Bismuth is the only naturally-occurring element that has no stable isotopes. Technetium and promethium are the other two elements that do not have any stable isotopes and are only found in trace amounts or are synthetically produced.
Is Uranium 235 used for production of electricity?
Yes, it is the only naturally occurring Uranium isotope that can be used, in fact it is the only naturally occurring isotope of any element that can be used and occurs in large enough quantities to be practical to use.
Why do elements have a listed average atomic mass and not just atomic mass?
Because most naturally occurring elements are a mixture of isotopes, each having a different atomic mass. These individual isotopic atomic masses must be combined accounting for the amount of each isotope of the element is present to get a weighted average atomic mass.
