2. Warm-Up
-Write the correct Nuclide Symbol for the following elements: *19 p+, 20 n *82 e-, 125n *Mass # 238, neutrons= 146

3. Isotopes
Atoms of the same elements have the same number of protons
HOWEVER there may be different numbers of neutrons and different mass numbers
When an element’s atom has different numbers of neutrons, it is said to have isotopes

4. Hydrogen’s Three Isotopes
Hydrogen has the following isotopes:
Protium-a hydrogen atom with one proton and NO neutrons
Deuterium-a hydrogen atom with one proton and only one neutron
Tritium-a hydrogen atom with one proton and two neutrons

5. The atomic mass unit is based on the relation of standard carbon-12
Average Atomic Mass
Atomic mass is the mass of an atom expressed in atomic mass units or amu
The atomic mass unit is based on the relation of standard carbon-12
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6. Average Atomic Mass Continued
Carbon-12 has a mass of amu
Example:
If an atoms weighs half as much as carbon-12, its atomic mass will be amu
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7. Example: If an atom weighs four times as much as carbon-12, it will have a mass of 48.000 00 amu

8. What is Atomic Mass?
The atomic mass that is reported in the periodic table is a weighted average based on the relative abundance of each element

9. Relative abundance refers to how common the isotope occurs in nature
Percent Abundance which refers to how many of each isotope are in every hundred

10. To Determine Avg. Atomic Mass
1) First convert relative abundance (%) to decimal equivalent
2) Multiply mass (in amu) by decimal equivalent
3) Add the numbers together
4) The sum (in amu) is the average atomic mass

11. For example, an element has two naturally occurring isotopes
For example, an element has two naturally occurring isotopes. One isotope has a relative abundance of % and a mass of amu. A second isotope has a relative abundance of 80.08% and a mass of amu. Calculate the atomic mass

12. Example
For example, an element has two naturally occurring isotopes. One isotope has a relative abundance of % and a mass of 7.02 amu. A second isotope has a relative abundance of 7.42% and a mass of amu. Calculate the atomic mass

13. Additional Example
Calculate the average atomic masses for the following: Isotope: Rel. Abund. Rel. Mass hydrogen % hydrogen % 2.014
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1.007 amu
1.0 amu (s.f.)

14. Practice
Titanium has five common isotopes: If the abundance of Ti- 46 is 8.0%, Ti-47 is 7.8 %, Ti-48 is 73.4 %, Ti-49 is 5.5% and Ti- 50 is 5.3 %. What is the average atomic mass of titanium?

15. Isotope Rel. Abund. Actual Mass O-16 99.762 15.995 O-17 0.038 16.999
Determine Avg. Atomic Mass for oxygen:
Isotope Rel. Abund Actual Mass O O O

16. Magnesium consists of three naturally occurring isotopes
Magnesium consists of three naturally occurring isotopes. The percent abundance of   these isotopes is as follows: 24Mg (78.70%), 25Mg (10.13%), and26Mg (11.7%). The average atomic mass of the three isotopes is amu. If the atomic mass of 25Mg is amu, and 26Mg is amu, calculate the actual atomic mass of 24Mg.   Answer : AMU

17. Why is the mass in amu of a carbon‐12 atom reported as 12
Why is the mass in amu of a carbon‐12 atom reported as in the periodic table of   the elements?
The masses on the periodic table are the average mass of all isotopes and their abundances found in the universe. Although carbon‐12 weighs exactly 12 amu, the periodic table reports that the mass is because we are taking into consideration the abundances and masses of the other two carbon isotopes (carbon‐13 and carbon‐ 14).

18. Copper used in electric wires comes in two flavors (isotopes): 63Cu and65Cu. 63Cu has an   atomic mass of amu and an abundance of 69.09%. The other isotope, 65Cu, has an   abundance of 30.91%. The average atomic mass between these two isotopes is amu. Calculate the actual atomic mass of 65Cu.  
Answer : Actual atomic mass of 65Cu = amu