Question

Simulation: Isotopes & Calculating Average Atomic Mass

Background
In this investigation you will learn about isotopes and average atomic mass calculations.
based upon the number of isotopes it has, as well as the mass and relative abundance of
Through your investigation you will determine the average atomic mass for an element
You can find the simulation here: teachchemistry.org/isotopes
each isotope.
TUTORIAL
PRACTICE
Carbon-12
-p-6
●n-6
●0-6
98.93%
abundance
Carbon-13
•p=6
•n=7
●0-6
1.07%
abundance
Tutorial
Click on the "Tutorial" tab at the top of the screen. You should see two carbon atoms.
Using the information on the screen, answer the following questions:
1. What is the difference(s) between the two carbon atoms shown on the screen?
2. What is the mass of each carbon atom on the screen?
3. In your own words, explain the meaning of isotope. Use the carbon atoms shown
on the screen as an example in your explanation.
4. What is the meaning of abundance? What effect do the abundancies have on the
element carbon, if any?

Answer 1

The difference between Carbon-12 and Carbon-13 is the number of neutrons; an isotope has the same number of protons but different neutrons resulting in varying atomic masses. Abundance affects the weighted average atomic mass, which for carbon is approximately 12.01 amu, calculated using the relative fractions and masses of its isotopes.

The differences between the two carbon atoms, Carbon-12 and Carbon-13, are in the number of neutrons they contain. Carbon-12 has 6 neutrons, while Carbon-13 has 7 neutrons. The mass of Carbon-12 is 12 atomic mass units (amu), and the mass of Carbon-13 is 13.003355 amu.

An isotope is a variant of an element that has the same number of protons but a different number of neutrons, resulting in a different mass number. For example, Carbon-12 and Carbon-13 are both isotopes of Carbon, but they differ in mass because of the additional neutron in Carbon-13.

The term abundance refers to the relative percentage of each isotope present in a naturally occurring sample of an element. The relative abundances of carbon isotopes affect the average atomic mass of carbon. Since Carbon-12 has a higher abundance (98.93%), it is more influential in calculating the average atomic mass of Carbon, which is approximately 12.01 amu.

To calculate the average atomic mass, the relative fraction of each isotope is multiplied by its mass and then summed. The equation is: average atomic mass = (abundance fraction of isotope 1 × mass of isotope 1) + (abundance fraction of isotope 2 × mass of isotope 2) + ... and so on for all isotopes.