Question

average atomic mass

1. based on model 1 and the table you created in question 4, for every 10 atoms of magnesium, about how many atoms of each isotope will be found?

model 2: natural abundance information for magnesium

isotope	natural abundance on earth (%)	atomic mass (amu)
$^{24}$mg	78.99	23.9850
$^{25}$mg	10.00	24.9858
$^{26}$mg	11.01	25.9826

1. consider the natural abundance information given in model 2.

a. calculate the expected number of atoms of each isotope that will be found in a sample of 20 atoms of mg. hint: the number of atoms must be a whole number!
b. is model 1 accurate in its representation of magnesium at the atomic level? explain.

1. if you could pick up a single atom of magnesium and put it on a balance, the mass of that atom would most likely be ________ amu. explain why.
2. find magnesium on the periodic table.

a. write down the decimal number shown in that box.
b. does the decimal number shown on the periodic table for magnesium match any of the atomic masses listed in model 2?

Explanation:

Step1: Calculate number of $^{24}$Mg atoms in 20 - atom sample

Multiply total atoms by $^{24}$Mg abundance.
$20\times\frac{78.99}{100}=20\times0.7899 = 15.798\approx16$

Step2: Calculate number of $^{25}$Mg atoms in 20 - atom sample

Multiply total atoms by $^{25}$Mg abundance.
$20\times\frac{10.00}{100}=20\times0.1 = 2$

Step3: Calculate number of $^{26}$Mg atoms in 20 - atom sample

Multiply total atoms by $^{26}$Mg abundance.
$20\times\frac{11.01}{100}=20\times0.1101 = 2.202\approx2$

Step4: Answer for 6b

Model 1 may not be accurate as it may not reflect the natural - abundance ratios precisely. Natural - abundance data from Model 2 gives a more accurate representation of the relative amounts of each isotope in a sample of magnesium atoms.

Step5: Answer for 7

The mass of a single magnesium atom is most likely 23.9850 amu because $^{24}$Mg has the highest natural abundance (78.99%), so it is the most common isotope and thus a randomly - selected magnesium atom is most likely to be $^{24}$Mg.

Step6: Answer for 8a

The decimal number shown on the periodic table for magnesium is approximately 24.3050.

Step7: Answer for 8b

No, the decimal number on the periodic table does not match any of the atomic masses listed in Model 2. The periodic - table value is the average atomic mass of all magnesium isotopes, weighted by their natural abundances.

Answer:

6a. $^{24}$Mg: 16 atoms, $^{25}$Mg: 2 atoms, $^{26}$Mg: 2 atoms
6b. Model 1 may not be accurate as it may not reflect natural - abundance ratios precisely.

1. 23.9850 amu because $^{24}$Mg has the highest natural abundance.

8a. 24.3050
8b. No