Final answer:
The atomic mass of boron is calculated using its two naturally occurring isotopes, B-10 and B-11, with a weighted average based on their relative abundances, resulting in an average atomic mass of 10.8 amu.
Step-by-step explanation:
The mass spectrum of boron shows peaks at m/z 10 and 11. This is because boron has two naturally occurring isotopes: B-10 and B-11. To calculate the atomic mass of boron, we multiply the mass of each isotope by its relative abundance and then sum these values. In a sample of boron, approximately 20% of the atoms are B-10 with a mass of about 10 amu, and the other 80% are B-11 with a mass of about 11 amu. Using the given abundances and isotope masses, the calculation for the atomic mass of boron is:
(0.20 × 10 amu) + (0.80 × 11 amu) = 2 amu + 8.8 amu = 10.8 amu
Therefore, the average atomic mass of boron atoms is 10.8 amu. It is important to note that no single boron atom has a mass of exactly 10.8 amu; this value is an average that takes into account the two different isotopes and their relative abundances.