Radiation Safety Practice Exam

What is the atomic mass of a lithium atom?

1. 3

2. 4

3. 5

4. 6

The correct answer is: 6

The atomic mass of a lithium atom refers to the weighted average mass of all the naturally occurring isotopes of lithium, measured in atomic mass units (amu). Lithium has two stable isotopes: lithium-6 and lithium-7. The most prevalent isotope is lithium-7, which has an atomic mass of approximately 7 amu, while lithium-6 has an atomic mass of about 6 amu. When calculating the average atomic mass based on natural abundance, lithium is generally represented as approximately 6.94 amu, which is commonly rounded to 7 in some contexts. However, in the options provided, focusing solely on the stable isotopes and their representations, the atomic mass is commonly approximated to 6 in summary atomic charts. Thus, the answer reflects the most common interpretation in basic chemistry contexts where lithium is rounded to 6 amu as its atomic mass.