1. Monday, November 17th, 2014 HW= Unit 3 Review Problems #1-10
Objective: We will be able to calculate the average atomic mass of an element based on isotope abundance.
Standard: IOD 401
Catalyst: According to Figure 2, which of the following minerals would most typically be found only in rocks of a medium grade?
A. Muscovite
B. Biotite
C. Kyanite
D. Plagioclase
Classroom expectations:
Wear Kenwood ID.
Cell phones, music players, and headphones are put away.
Food is disposed of or put away.
Dressed appropriately.
Notebook is out and you are ready for today’s class.
Table of Contents:
11/ Week 12 Catalyst Chart
11/ Unit 3 Review (do NOT staple, turning in)
11/ Notes: Calculating Average Atomic Mass/w Practice

2. Announcements Test THIS FRIDAY!!!
Tutoring Tuesday and Wednesday THIS WEEK!!
NO HELP AVAILABLE FROM MS. INGHAM THURSDAY!!
There WILL BE a notebook check before Thanksgiving break!!

3. Agenda Catalyst/Announcements Homework Check/Review
Notes: Calculating Average Atomic Mass
Practice Problems
Practice Wkst

4. Agenda Problems
An isotope is the same atom (same amount of protons) with a different mass (different amount of neutrons)
14) The average atomic mass will be closer to 63 amu because the isotope with the mass of 63amu is more abundant.
15) amu
16) amu
17) amu or amu

5. Calculating Average Atomic Mass
Pg 73

6. Isotopes Recall
Atoms with the same number of protons, but different numbers of neutrons.
Atoms of the same element (same atomic number) with different mass numbers
Isotopes of Chlorine
35 Cl 37 Cl
Chlorine Chlorine - 37

7. Isotopes Recall
Despite these differences, isotopes are chemically alike because they have identical numbers of protons and electrons.
Neon-20, neon-21, and neon-22 are three isotopes of neon, a gaseous element used in lighted signs. Comparing and Contrasting How are these isotopes different? How are they similar?

8. Isotopes Recall Isotope Protons Electrons Neutrons Nucleus Hydrogen–1
(protium) 1
Hydrogen-2
(deuterium)
Hydrogen-3
(tritium) 2

9. Review: Check for Understanding
Fluorine has an atomic number of 9. Write out the name of the isotope of fluorine that has 8 neutrons.
Fluorine-17

10. Review: Check for Understanding
Fluorine has an atomic number of 9. Write out the SYMBOL of the isotope of fluorine that has 10 neutrons.
Mass #  19 F
Atomic #  9

11. Review: Check for Understanding
Three isotopes of chromium are chromium-50, chromium-52, and chromium-53. How many neutrons are in each isotope, given that chromium has an atomic number of 24?
Chromium-50:
50-24 = 26
Chromium-52:
52-24 = 28
Chromium-53:
53-24 = 29

12. Average Atomic Mass What is average atomic mass?
Average atomic mass is the weighted average of the atomic masses of the naturally occurring isotopes of an element
The average mass on the periodic table is closest to the ISOTOPE of GREATEST abundance

13. Check for Understanding
The average atomic mass of Carbon, C, is amu. Predict which isotope has the greatest percent abundance based upon the average atomic mass.
Carbon – 10
Carbon – 12
Carbon – 13
Carbon -- 14

14. Calculating Average Atomic Mass
To calculate the atomic mass of an element, multiply the mass of each isotope by its percent abundance, expressed as a decimal, and then add the products.
Reminder: To express a percent as a decimal move the decimal 2 places to the left
ex: 89.97% =

15. Calculating AverageAtomic Mass
(Mass isotope # 1) (% Abundance as a decimal) +
(Mass isotope # 2 ) ( % Abundance as a decimal)
(Mass isotope # 3) ( % Abundance as a decimal )
+ …..

16. Calculating a Weighted Average
Example
A box contains two size of marbles. If
25.0% have masses of 2.00 g and 75.0%
have masses of 3.00 g what is the weighted
average?
(.250) (2.00) + (.750) (3.00) = =
2.75g

17. Whiteboard Practice Show all of your work when completing the problem.
DO NOT hold up your board until told to do so.

18. Practice Problem #1 EXAMPLE Boron has two isotopes:
B-10 (mass amu) 19.8% abundance
B-11 (mass amu) 80.2% abundance
Calculate the average atomic mass.
(.198) (10.013) + (.802) ( ) =
1.98 amu amu =
10.81 amu

19. Calculating Average Atomic Mass
Calculate the average atomic mass of Mg.
Isotope amu (78.99%)
Isotope amu (10.00%)
Isotope 3 – amu (11.01%)
(23.985)(.7899)+(24.986)(.1000)+(25.982)(.1101)
18.95 amu amu amu =
24.31 amu

20. Average Atomic Mass
Helium has two naturally occurring isotopes, He-3 and He-4. The atomic mass of helium is amu. Which isotope is more abundant in nature? Explain.
He-4 is more abundant in nature because the atomic mass is closer to the mass of He-4 than to the mass of He-3.

21. Practice Worksheet
Complete the problems on the practice worksheet making sure to show all work when necessary.