Two stable isotopes of lithium `._3^6Li` and `._3^7Li` have respective abundances of 7.5% and 92.5% . These isotopes have masses 6.0152 u and 7.016004 u respectively. Find the atomic weight of lithium

Explanation

To find the atomic weight of lithium given the isotopes and their respective abundances, we can follow these steps:

### Step 1: Identify the isotopes and their properties
- Isotope 1: \(_3^6Li\)
- Abundance = 7.5% = 0.075 (as a decimal)
- Mass = 6.0152 u
- Isotope 2: \(_3^7Li\)
- Abundance = 92.5% = 0.925 (as a decimal)
- Mass = 7.016004 u

### Step 2: Calculate the contribution of each isotope to the atomic weight
- Contribution of \(_3^6Li\):
\[ \text{Contribution of } \, _3^6Li = \text{Abundance} \times \text{Mass} = 0.075 \times 6.0152 \]

- Contribution of \(_3^7Li\):
\[ \text{Contribution of } \, _3^7Li = \text{Abundance} \times \text{Mass} = 0.925 \times 7.016004 \]

### Step 3: Perform the calculations
- Calculate the contribution of \(_3^6Li\):
\[ 0.075 \times 6.0152 = 0.45114 \, \text{u} \]

- Calculate the contribution of \(_3^7Li\):
\[ 0.925 \times 7.016004 = 6.497954 \, \text{u} \]

### Step 4: Sum the contributions to find the atomic weight
- Total atomic weight of lithium:
\[ \text{Atomic weight} = 0.45114 + 6.497954 = 6.949094 \, \text{u} \]

### Step 5: Round the result
- Rounding to two decimal places, we get:
\[ \text{Atomic weight of lithium} \approx 6.94 \, \text{u} \]

### Final Result
The atomic weight of lithium is approximately **6.94 u**.

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