average atomic mass

[angel oganesyan]

hi :) i was wondering if anybody knew if average atomic mass questions have come up in any of the review sessions or homework assignments or even midterms since i heard some people in class talking about it but never recalled learning it or going over it. thank you in advance for any input!

[706244927]

I don't recall any specific in class examples, but I do remember average atomic mass questions from AP Chem:

First of all, the atomic mass is the mass of an atom obtained by finding the average mass of the isotopes (atoms with the same number of protons but different numbers of neutrons) of a given element.

How to Calculate Average Atomic Mass:
Step 1: Identify the percentage of each isotope in the composition of the element and its mass.

Step 2: For each isotope, multiply its mass by the percent.

Step 3: Add the results for all the isotopes from Step 2. This is the average atomic mass of the given element.

Example problem: Calculate the average atomic mass of boron given that 19.8% of its naturally occurring atoms have a mass of 10.013 amu and 80.2% have a mass of 11.009 amu.

Step 1: Identify the percentage of each isotope in the composition of the element and its mass.

Boron isotope A has 10.013 amu and composes 19.8% of natural boron.

Copper isotope B has 11.009 amu and composes 80.2% of natural boron.

Step 2: For each isotope, multiply its mass by the percent.
ISOTOPE A: (10.013 amu)(19.8%)= 1.983amu
ISOTOPE B: (11.009amu)(80.2%)=8.829amu

Step 3: Add the results for all the isotopes from step 2. This is the average atomic mass of the given element.
Average atomic mass= 1.983amu + 8.829amu

The average atomic mass of boron is 10.812 amu.