Lithium has elemental isotopic mass of 6.941 and has two naturally occurring isotopes Li-6 and Li-7. Their masses are 6.0151 amu and 7.0160 respectively. What are the natural abundances of the isotopes of Lithium?

To find the natural abundances of the isotopes Li-6 and Li-7, we can use the concept of weighted average:

Given:
- The average atomic mass of lithium is 6.941 amu.
- The masses of the isotopes are:
  - \( \text{Li-6} = 6.0151 \, \text{amu} \)
  - \( \text{Li-7} = 7.0160 \, \text{amu} \)

Let \( x \) be the natural abundance of Li-6 (expressed as a fraction), and \( (1 - x) \) be the natural abundance of Li-7. 

The average atomic mass is given by the weighted average formula:

\[
6.941 = (x \times 6.0151) + [(1 - x) \times 7.0160]
\]

Now, let's solve this equation to find \( x \).

\[
6.941 = 6.0151x + 7.0160 - 7.0160x
\]

\[
6.941 = 6.0151x - 7.0160x + 7.0160
\]

\[
6.941 - 7.0160 = -1.0009x
\]

\[
-0.075 = -1.0009x
\]

\[
x = \frac{0.075}{1.0009} \approx 0.0749
\]

So, the natural abundance of Li-6 is approximately 7.49%, and the natural abundance of Li-7 is:

\[
1 - 0.0749 = 0.9251
\]

This corresponds to approximately 92.51%.

### Summary:
- **Natural abundance of Li-6**: \( \approx 7.49\% \)
- **Natural abundance of Li-7**: \( \approx 92.51\% \)

Would you like more details on the calculation or have any questions?

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**Related Questions**:
1. How does the concept of isotopic mass relate to the calculation of average atomic mass?
2. What is the importance of knowing the natural abundance of isotopes in chemistry?
3. Can isotopic abundances be different on other planets?
4. How do you measure the isotopic mass of an element experimentally?
5. What other elements have naturally occurring isotopes?

**Tip:** When dealing with isotopic abundance problems, always check that the sum of the fractional abundances equals 1 (or 100%).

Learn how to calculate the natural abundances of lithium isotopes Li-6 and Li-7 using the weighted average formula. Understand the concept of isotopic mass and fractional abundance in chemistry. Suitable for high school students and chemistry enthusiasts.

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