Final answer:
The atomic mass of an element, the weighted average of the isotopes' masses based on their natural abundances is taken. An example is provided using boron isotopes. Without natural abundance data, the exact atomic mass of the element with isotopes of 112.9 amu and 114.9 amu cannot be determined.
Step-by-step explanation:
The atomic mass of an element that has naturally occurring isotopes can be determined by calculating the weighted average of the isotopes' masses. To calculate the atomic mass of the element, we need to know the respective percentages of each isotope in nature. Unfortunately, the provided information about the two isotopes with atomic masses of 112.9 amu and 114.9 amu is incomplete since the natural abundances of the isotopes are missing.
As an example of how to calculate the average atomic mass when natural abundances are known, let's consider the element boron. In a sample of boron, 20% of the atoms are B-10 with a mass of 10 amu, and the remaining 80% are B-11 with a mass of 11 amu. The atomic mass of boron is therefore calculated as follows:
Boron average mass = (20% × 10 amu) + (80% × 11 amu) = 2 amu + 8.8 amu = 10.8 amu.
Without knowing the natural abundances of the two isotopes mentioned in the question, it is not possible to calculate an exact atomic mass for that element.