Question

You are conducting an experiment with Thallium, which has two isotopes, Thallium-203 and Thallium-205. Thallium's atomic number is 81. The percent abundance of the two isotopes, respectively, is Thallium-203: 35% and Thallium-205: 65%. Please calculate the average atomic mass of Thallium.

A) 203.55 amu
B) 204.35 amu
C) 204.85 amu
D) 205.25 amu

Answer 1

The average atomic mass of Thallium is calculated by multiplying each isotope's abundance by its atomic mass and adding the results. The calculation yields an average atomic mass of approximately 204.3 amu, which corresponds to option B) 204.35 amu.

Step-by-step explanation:

To calculate the average atomic mass of Thallium, which has isotopes Thallium-203 and Thallium-205, we need to consider the isotopes' respective percent abundances and atomic masses.

First, convert the percent abundances to decimal form by dividing by 100:

• Thallium-203: 35% or 0.35
• Thallium-205: 65% or 0.65

Next, multiply each isotope's abundance by its atomic mass and add the results together:

1. (0.35 × 203 amu) = 71.05 amu for Thallium-203
2. (0.65 × 205 amu) = 133.25 amu for Thallium-205

Adding both contributions gives us the average atomic mass of Thallium:

71.05 amu + 133.25 amu = 204.3 amu

The closest answer from the provided options is B) 204.35 amu.