The average atomic mass of nitrogen is calculated by considering the masses of its isotopes and their relative abundances. The standard atomic weight of Nitrogen is 14.0067 u.
Understanding Average Atomic Mass
Average atomic mass is not simply an average of the mass numbers of all isotopes. It's a weighted average, taking into account how frequently each isotope appears in nature.
Steps to Calculate Average Atomic Mass:
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Identify the Isotopes: Determine all the isotopes of the element you're interested in. For nitrogen, the most common isotopes are Nitrogen-14 (14N) and Nitrogen-15 (15N).
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Determine Isotopic Masses: Find the accurate mass of each isotope. These masses are usually very close to the mass number (the number of protons and neutrons), but are more precise.
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Determine Relative Abundances: Find the percentage or decimal abundance of each isotope. This represents the fraction of atoms of that element that are of a particular isotope. Abundances are often found on the periodic table or in isotopic data tables.
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Calculate the Weighted Average: Multiply the mass of each isotope by its relative abundance (in decimal form). Then, sum these products together.
Average Atomic Mass = (Mass of Isotope 1 × Abundance of Isotope 1) + (Mass of Isotope 2 × Abundance of Isotope 2) + ...
Example Calculation (Simplified)
Let's say we have the following (simplified for illustration) data for nitrogen:
| Isotope | Mass (u) | Abundance (%) | Abundance (decimal) |
|---|---|---|---|
| Nitrogen-14 | 14.003 | 99.6% | 0.996 |
| Nitrogen-15 | 15.000 | 0.4% | 0.004 |
Average Atomic Mass = (14.003 u × 0.996) + (15.000 u × 0.004) = 13.947 + 0.060 = 14.007 u
The actual value, as given in the reference, is 14.0067 u, reflecting more precise isotopic masses and abundances.
Reference Information
- 14.0067 u Nitrogen / Atomic mass
This tells us that the standard atomic weight, which is an average, of nitrogen is 14.0067 atomic mass units (u).
