Naturally occurring lithium (Li) consists of only two isotopes, Li-6 (6.02 amu) and Li-7 (7.02 amu), where the exact isotopic masses are given in parentheses. Use the periodic table and determine which isotope is present in the larger percentage in the natural element.
C) The percentage of each isotope is about the same.
D) The relative percent abundance cannot be determined from the information available.

Question

Naturally occurring lithium (Li) consists of only two isotopes, Li-6 (6.02 amu) and Li-7 (7.02 amu), where the exact isotopic masses are given in parentheses. Use the periodic table and determine which isotope is present in the larger percentage in the natural element.
C) The percentage of each isotope is about the same. 
D) The relative percent abundance cannot be determined from the information available.

Quizplus · Accepted Answer

The atomic mass of naturally occurring lithium (6.941 amu) is closer to the mass of Li-7 (7.02 amu) than to the mass of Li-6 (6.02 amu). This indicates that Li-7 is present in the larger percentage in the natural element.

Naturally Occurring Lithium (Li) Consists of Only Two Isotopes, Li-6