Determining Average Atomic Mass of Elements: Isotopes and Percentages, Study notes of Chemistry

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Average Atomic Mass

Defining and Determining

What is an element?

An element is defined by the number of protons (not neutrons or electrons).

Using the cards, sort the cards into piles of like elements.

Average

What does average mean?

Average is a middle number it could be the mean, median, or mode which describes a set of data.

Average Atomic Mass:

It is the average mass of each isotope by the factional representation in a given sample for a specific element.

How to Calculate

1. First you need to read the problem.
2. Second you will need to convert all the percentages to decimals.
3. Next, for each percentage now in decimals you multiply it by the isotopes reported mass.
4. After each pair has been multiplied, you then add all the masses together.
5. Check the mass for that element as reported on the periodic table!

3. Multiply each by the mass

0.075 * 6 amu =

0.925 * 7 amu =

0.075 * 6 amu = 0.45 amu

0.925 * 7 amu = 6.475 amu

4. Add together

0.45 amu + 6.475 amu = 6.925 amu

5. Check PT

6.941 amu = very close (due to rounding)

Now you try with a partner

(^10) B has a percent abundance of 19.8% and 11 B

has a percent abundance of 80.2%. What is the average atomic mass of Boron (B)?

Neon

(^20) Ne 90.51%, 21 Ne 0.21%, and 22 Ne 9.22%

Find the average atomic mass of Ne (neon).

(0.905120 amu) + (0.002121 amu) + (0.0922*22 amu) = 20.1745 amu