The abundances of chemical elements measures how relatively common or rare that particular element is, or how much of the element is present in a given environment by comparison to all other elements. According to the websters dictionary the definition of abundance is an oversufficient quantity or supply.

By definition abundance may refer to:
In Science and Technology
  • Abundance (Economics): The opposite of scarcities
  • Abundance (Food): Growing food or crops with plentiful resources that will not run out
  • Abundance (Ecology): The relative represenation of a species in a community
In Chemistry
  • Abundance (Chemistry): When a substance in a reaction is present in high quantities
  • Abundance of the chemical elements: a measure of how common elements are
  • Natural Abundance: The natural prevalence of different isotopes of an element on Earth

The Abundance of a chemical elements measures how realtively common (or rare) the element, is, or how much of the element is present in a given environment by comparison to all other elements. Abundance may be variously measured by the mass-friction (the same as weight fraction) or mole-fraction (fraction of atoms by numerical count, or sometimes fraction of molecules in gasses) or by volumne-fraction. Measurement by volume-fraction is a common abundance measure in mixed gases such as planetary atmospheres, and is close to molecular mole-fraction for ideal gas mixtures (i.e., gas mixtures at relatively low densities and pressures).
For example, the mass-fraction abundance of oxygen and water is about 89%, because that is the fraction of water's mass which is oxygen. However, the mole-fraction abundance of oxygen in water is only 33% because only 1 atom of 3 in water is an oxygen atom. In the universe as a whole, and in the atompsheres of gas giant planets such as Jupiter, the mass-fraction abundances of hydrogen and helium are about 74% and 23–25% respectively, while the (atomic) mole-fractions of these elements are closer to 92% and 8%. However, since hydrogen is diatomic while helium is not, in the conditions of Jupiter's outer atomsphere,, the molecular mole-fraction (fraction of total gas molecules, or fraction of atmosphere by volume) of hydrogen in the outer atmosphere of Jupiter is about 86%, and for helium, 13%.

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Hydrogen and helium are two of the most abundant substances in the universe.
Oxygen is the MOST abundant element on Earth.
In the Milky Way, there are 10 highly abundant elements (including the elements listed above):
-Carbon -Neon -Iron -Nitrogen -Silicon -Magnesium -Sulfur

Example #1: Nitrogen is made up of two isotopes, N-14 and N-15. Given nitrogen's atomic weight of 14.007, what is the percent abundance of each isotope?
Here's the solution:
  • (14.003074) (x) + (15.000108) (1 - x) = 14.007
external image Elemental_abundances.svg