Calculate The Atomic Mass for Lithium Given The Following Informaiton
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Lithium (Li) is a chemical element with atomic number 3. Its atomic mass is typically calculated using the weighted average of its naturally occurring isotopes, taking into account their relative abundances. This guide explains how to calculate the atomic mass of lithium given isotope data.
How to calculate atomic mass
The atomic mass of an element is calculated by finding the weighted average of the masses of its isotopes, based on their natural abundances. This accounts for the fact that different isotopes of an element may have slightly different masses.
Steps to calculate atomic mass
- Identify the isotopes of the element and their atomic masses.
- Determine the natural abundance (percentage) of each isotope.
- Multiply each isotope's atomic mass by its abundance (expressed as a decimal).
- Sum these products to get the weighted average atomic mass.
For lithium, the two naturally occurring isotopes are lithium-6 (6Li) and lithium-7 (7Li). Their atomic masses are approximately 6.0151 u and 7.0160 u, respectively.
Formula used
The atomic mass (AM) is calculated using the formula:
Where:
- Mass of Isotope = Atomic mass of the isotope in atomic mass units (u)
- Abundance of Isotope = Natural abundance of the isotope (expressed as a decimal between 0 and 1)
For lithium with two isotopes:
Worked example
Let's calculate the atomic mass of lithium given the following isotope data:
| Isotope | Atomic Mass (u) | Natural Abundance (%) |
|---|---|---|
| 6Li | 6.0151 | 7.59% |
| 7Li | 7.0160 | 92.41% |
Calculation:
The calculated atomic mass of lithium is approximately 6.9576 atomic mass units.
FAQ
- What is the difference between atomic mass and atomic weight?
- Atomic mass and atomic weight are often used interchangeably, but technically atomic mass refers to the mass of a single atom of an element, while atomic weight refers to the average mass of atoms in a sample, taking into account isotopic distribution.
- Why is the atomic mass of lithium not a whole number?
- The atomic mass of lithium is not a whole number because it is the weighted average of the masses of its isotopes, which have slightly different masses. This accounts for the natural abundance of each isotope.
- How accurate are atomic mass calculations?
- Atomic mass calculations are very accurate, typically within a few parts per million, based on precise measurements of isotopic abundances and atomic masses. The values used in this calculator are based on the most recent IUPAC (International Union of Pure and Applied Chemistry) recommended values.