Question

A hypothetical element has two main isotopes with mass numbers of 56 and 59. If 84.00% of the isotopes have a mass number of 56 amu, what atomic weight should be listed on the periodic table for this element? (Answer in units of amu)

Answer 1

The atomic weight for a hypothetical element with isotopes of mass numbers 56 amu and 59 amu, with respective abundances of 84.00% and 16.00%, is calculated to be 56.48 amu.

Step-by-step explanation:

To calculate the atomic weight of a hypothetical element with two main isotopes having mass numbers of 56 amu and 59 amu, one with an abundance of 84.00%, we use the weighted average formula:

Atomic Weight = (Mass of isotope 1 × Abundance of isotope 1) + (Mass of isotope 2 × Abundance of isotope 2)

For the first isotope (mass number 56 amu), the abundance is 84.00%, or 0.8400 as a decimal. The second isotope (mass number 59 amu) thus has an abundance of 100% - 84.00% = 16.00%, or 0.1600.

Now, we calculate the average atomic mass:

(56 amu × 0.8400) + (59 amu × 0.1600) = 47.04 amu + 9.44 amu = 56.48 amu

Therefore, the atomic weight that should be listed on the periodic table for this element is 56.48 amu.