Lithium has two naturally occurring isotopes: lithium-6 (mass = 6.015 u, abundance = 4%) and lithium-7 (mass = 7.016 u, abundance = 96%). What is the average atomic mass of lithium?

• A. 6.10 u
• B. 6.94 u
• C. 7.00 u
• D. 6.50 u

Answer: (B)

Verified step by step guidance

1. Identify the isotopes of lithium and their respective masses and abundances: lithium-6 with mass 6.015 u and abundance 4%, and lithium-7 with mass 7.016 u and abundance 96%.
2. Convert the percentage abundances into decimal form by dividing by 100: 4% becomes 0.04 and 96% becomes 0.96.
3. Use the formula for average atomic mass, which is the weighted average of the isotopic masses based on their abundances: \[\text{Average atomic mass} = (\text{mass of isotope 1} \times \text{abundance of isotope 1}) + (\text{mass of isotope 2} \times \text{abundance of isotope 2})\]
4. Substitute the values into the formula: \[\text{Average atomic mass} = (6.015 \times 0.04) + (7.016 \times 0.96)\]
5. Calculate each product separately and then add them together to find the average atomic mass of lithium.