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What is an isotope? What is meant by the phrase “percent abundance in nature”? Explain the difference between average and a weighted average. Highlight evidence if you can and site which paragraph and line you found the evidence.

What is an isotope? What is meant by the phrase “percent abundance in nature”? Explain the difference between average and a weighted average. Highlight evidence if you can and site which paragraph and line you found the evidence.

Chemistry by OpenStax (2015-05-04)
Chemistry by OpenStax (2015-05-04)
1st Edition
ISBN:9781938168390
Author:Klaus Theopold, Richard H Langley, Paul Flowers, William R. Robinson, Mark Blaser
Publisher:Klaus Theopold, Richard H Langley, Paul Flowers, William R. Robinson, Mark Blaser
Chapter2: Atoms, Molecules, And Ions
Section: Chapter Questions
Problem 24E: Variations in average atomic mass may be observed for elements obtained from different sources....
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Read-To find the average atomic mass of neon, we will use the equation above and take the abundance of the first isotope times the mass of the first isotope plus the abundance of the second isotope times the mass of the second isotope plus the abundance of the third isotope times the mass of the third isotope. The equation would then look like: = (0.9048x19.9924)+(0.0027x20.9938 amu) + (0.0925x21.9914 amu)=18.089 amu +0.0516 amu +2.034 amu=20.18 amu. This is the average atomic mass of neon. Answer the questions What is an isotope? What is meant by the phrase “percent abundance in nature”? Explain the difference between average and a weighted average. Highlight evidence if you can and site which paragraph and line you found the evidence.
Breath in... Breath out: Again! When you inhale air, you are not just inhaling a mixture of oxygen, nitrogen, and trace gasses, but a mixture of different oxygen atoms and different nitrogen atoms. It turns out that all oxygen atoms have the same number of protons, but some may have different numbers of neutrons. These different-but-still-oxygen atoms are called isotopes. Some atoms have just two isotopes; some have dozens! The average atomic mass is an experimental number determined from all of the naturally occurring isotopes of an element. Not all atoms of an element are identical. For example, chlorine has two different isotopes that occur in nature; chlorine-35 and chlorine-37. When you look at chlorine on the Periodic Table it has an average atomic mass of 35.45 amu. This number is the weighted average of the masses of both isotopes, not just one of them. Notice that the units were listed as amu, which stands for atomic mass units. This unit is based off the mass of the isotope 12C (carbon-12). Carbon-12 was chosen as the basis for all of the masses on the periodic table and has been defined to be exactly 12 amu. So all of the other masses on the period table are relative to the mass of carbon-12. In that case, then why is the atomic mass of carbon on the periodic table not exactly 12 amu? Because not all carbon in nature is 12C! Most of 12C, some of it is 13C, and a very tiny amount is 14C. When these are averaged together you get the a ge atomic mass shown on the periodic table of 12.01 amu. Since the abundances are not equal, we cannot do a typical simple average where we just add them up and divide by two. Instead, we need to perform a weighted average. The formula to calculate the average atomic mass is:
Transcribed Image Text:Breath in... Breath out: Again! When you inhale air, you are not just inhaling a mixture of oxygen, nitrogen, and trace gasses, but a mixture of different oxygen atoms and different nitrogen atoms. It turns out that all oxygen atoms have the same number of protons, but some may have different numbers of neutrons. These different-but-still-oxygen atoms are called isotopes. Some atoms have just two isotopes; some have dozens! The average atomic mass is an experimental number determined from all of the naturally occurring isotopes of an element. Not all atoms of an element are identical. For example, chlorine has two different isotopes that occur in nature; chlorine-35 and chlorine-37. When you look at chlorine on the Periodic Table it has an average atomic mass of 35.45 amu. This number is the weighted average of the masses of both isotopes, not just one of them. Notice that the units were listed as amu, which stands for atomic mass units. This unit is based off the mass of the isotope 12C (carbon-12). Carbon-12 was chosen as the basis for all of the masses on the periodic table and has been defined to be exactly 12 amu. So all of the other masses on the period table are relative to the mass of carbon-12. In that case, then why is the atomic mass of carbon on the periodic table not exactly 12 amu? Because not all carbon in nature is 12C! Most of 12C, some of it is 13C, and a very tiny amount is 14C. When these are averaged together you get the a ge atomic mass shown on the periodic table of 12.01 amu. Since the abundances are not equal, we cannot do a typical simple average where we just add them up and divide by two. Instead, we need to perform a weighted average. The formula to calculate the average atomic mass is:
Since the abundances are not equal, we cannot do a typical simple average where we just add them up and divide by two. Instead, we need to perform a weighted average. The formula to calculate the average atomic mass is: average atomic mass = [(relative abundance x mass of isotope) Remember that is the symbol for sum. In other words, we will take the sum of the relative abundance of each isotope multiplied by its mass. Example Neon has three naturally occurring isotopes. Symbol Ne-20 Ne-21 Ne-22 Mass Isotopic mass Percent natural number (amu) abundance 20 21 22 19.9924 20.9938 21.9914 90.48% 0.27% 9.25% ….. Remember that mass number is not the same as the atomic mass or isotopic mass! The mass number is the number of protons + neutrons, while atomic mass (or isotopic mass) is the mass if you were to somehow weigh it on a balance.
Transcribed Image Text:Since the abundances are not equal, we cannot do a typical simple average where we just add them up and divide by two. Instead, we need to perform a weighted average. The formula to calculate the average atomic mass is: average atomic mass = [(relative abundance x mass of isotope) Remember that is the symbol for sum. In other words, we will take the sum of the relative abundance of each isotope multiplied by its mass. Example Neon has three naturally occurring isotopes. Symbol Ne-20 Ne-21 Ne-22 Mass Isotopic mass Percent natural number (amu) abundance 20 21 22 19.9924 20.9938 21.9914 90.48% 0.27% 9.25% ….. Remember that mass number is not the same as the atomic mass or isotopic mass! The mass number is the number of protons + neutrons, while atomic mass (or isotopic mass) is the mass if you were to somehow weigh it on a balance.
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