What is Atomic Mass?

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What is Atomic Mass?

  1. 1. Launch: 9/16 <ul><li>4. How does atomic number vary throughout the periodic table? </li></ul><ul><ul><li>a. it is fixed and does not change as you move across the periodic table </li></ul></ul><ul><ul><li>b. it decreases from left to right, and from top to bottom </li></ul></ul><ul><ul><li>c. it increases from left to right, and from top to bottom </li></ul></ul><ul><ul><li>d. it increases from right to left, and from top to bottom </li></ul></ul><ul><li>1. All atoms of an element have </li></ul><ul><ul><li>a. the same number of protons. </li></ul></ul><ul><ul><li>b. the same number of neutrons. </li></ul></ul><ul><ul><li>c. the same number of electrons. </li></ul></ul><ul><ul><li>d. neither mass nor volume. </li></ul></ul>
  2. 2. What is atomic mass? Mr. Heffner Chemistry 9/15/09
  3. 3. What is an element? <ul><li>All atoms in a specific element have the same atomic number </li></ul><ul><ul><li>Atomic number = # of protons </li></ul></ul><ul><li>The periodic table is organized by increasing atomic number </li></ul>
  4. 4. What is atomic mass? <ul><li>Atomic mass is… </li></ul><ul><ul><li>the number of protons and neutrons in an atom </li></ul></ul><ul><ul><li>the number of particles in the nucleus </li></ul></ul><ul><li>Mass = weight </li></ul><ul><ul><li>So, atomic mass is the weight of an atom </li></ul></ul><ul><ul><li>Units = amu (atomic mass units) </li></ul></ul>
  5. 5. What is an element? Atomic number Symbol Name Atomic mass <ul><ul><li>4.00 </li></ul></ul><ul><ul><li>2 </li></ul></ul><ul><ul><li>He </li></ul></ul><ul><ul><li>Helium </li></ul></ul>
  6. 6. What is atomic mass? <ul><li>Atomic mass vs. atomic number </li></ul>Mass Number <ul><li>Protons + neutrons </li></ul><ul><li>Just protons </li></ul><ul><li>Weight of atom </li></ul><ul><li>What defines atom </li></ul><ul><li>On bottom </li></ul><ul><li>On top </li></ul><ul><li>Decimal </li></ul><ul><li>Whole-number </li></ul>
  7. 7. What is atomic mass? <ul><li>How to calculate the number of neutrons </li></ul><ul><li>Atomic mass – atomic number = # of neutrons </li></ul><ul><li>How many neutrons does He (Helium) have? </li></ul><ul><li>4 – 2 = 2 neutrons </li></ul><ul><li>How many neutrons does Li (Lithium) have? </li></ul><ul><li>7 – 3 = 4 neutrons </li></ul>
  8. 8. Summary <ul><li>Atomic mass is the number of protons and neutrons in an atom </li></ul><ul><li>Atomic mass – atomic number = # of neutrons </li></ul>
  9. 9. Foldable <ul><li>Fold in half 3X, then unwrap and fold in windows </li></ul><ul><ul><li>Cut with scissors </li></ul></ul><ul><ul><li>3 hole-punch </li></ul></ul><ul><li>Terms: only 2! </li></ul><ul><ul><li>Atomic mass </li></ul></ul><ul><ul><li>Neutron (charge, mass, location) </li></ul></ul><ul><li>Quiz yourself when finished </li></ul>
  10. 10. Practice Questions <ul><li>Answer the following in complete sentences: </li></ul><ul><li>What is atomic mass? </li></ul><ul><li>How is atomic mass different from atomic number? </li></ul><ul><li>Draw and label the representation of C (Carbon) including atomic mass. </li></ul><ul><li>How many neutrons do the atoms of the following elements have? </li></ul><ul><ul><li>N (Nitrogen) </li></ul></ul><ul><ul><li>Mg (Magnesium) </li></ul></ul><ul><ul><li>Au (Gold) </li></ul></ul>
  11. 11. What is atomic mass? <ul><li>Trend for atomic number </li></ul><ul><ul><li>INCREASES from Left to Right </li></ul></ul><ul><ul><li>INCREASES from Top to Bottom </li></ul></ul><ul><li>An exception to the rule! </li></ul><ul><ul><li>Co (Cobalt) and Ni (Nickel) </li></ul></ul><ul><ul><li>The periodic table is organized by atomic number, so Co must come before Ni </li></ul></ul>
  12. 12. What is an isotope? <ul><li>What is going on here? </li></ul><ul><ul><li>Why are there exceptions? </li></ul></ul><ul><ul><li>Why are atomic masses not whole numbers? </li></ul></ul><ul><li>An isotope is… </li></ul><ul><ul><li>an atom that has the same number of protons as other atoms of the same element, but has a different number of neutrons </li></ul></ul><ul><ul><li>the same atomic number, but a different atomic mass </li></ul></ul>
  13. 13. What is an isotope? <ul><li>Most elements have a few stable isotopes </li></ul><ul><ul><li>Carbon-12, atomic mass = 12.00 </li></ul></ul><ul><ul><li>Carbon-13, atomic mass = 13.00 </li></ul></ul><ul><ul><li>Carbon-14, atomic mass = 14.00 </li></ul></ul><ul><li>Why is atomic mass a decimal? </li></ul><ul><ul><li>Because it is an average of the masses of the naturally occurring isotopes </li></ul></ul>
  14. 14. What is an isotope? <ul><li>How to calculate the number of neutrons in isotope </li></ul><ul><li>Atomic mass – atomic number = # of neutrons </li></ul><ul><li>How many neutrons does Carbon-13 have? </li></ul><ul><li>13 – 6 = 7 neutrons </li></ul><ul><li>How many neutrons does Carbon-14 have? </li></ul><ul><li>14 – 6 = 8 neutrons </li></ul>
  15. 15. Summary <ul><li>Atomic mass INCREASES from </li></ul><ul><ul><li>Left  Right </li></ul></ul><ul><ul><li>Top  Bottom </li></ul></ul><ul><li>Isotopes have a different number of neutrons </li></ul><ul><ul><li>Atomic mass = average mass = decimal </li></ul></ul><ul><li>Atomic mass – atomic number = # neutrons </li></ul>
  16. 16. Foldable <ul><li>Fold in half 3X, then unwrap and fold in windows </li></ul><ul><ul><li>Cut with scissors </li></ul></ul><ul><ul><li>3 hole-punch </li></ul></ul><ul><li>Terms: only 2! </li></ul><ul><ul><li>Isotope </li></ul></ul><ul><ul><li>Trend for atomic number and atomic mass </li></ul></ul><ul><li>Quiz yourself when finished </li></ul>
  17. 17. Practice Questions <ul><li>Answer the following in complete sentences: </li></ul><ul><li>What is an isotope? </li></ul><ul><li>Why is Co placed before Ni on the periodic table? </li></ul><ul><li>Why is atomic mass a decimal and not a whole #? </li></ul><ul><li>What is the trend for atomic mass? </li></ul><ul><li>How many protons and neutrons are in: </li></ul><ul><ul><li>K </li></ul></ul><ul><ul><li>P </li></ul></ul><ul><ul><li>Hydrogen-2 </li></ul></ul><ul><ul><li>Oxygen-18 </li></ul></ul>
  18. 18. Exit Slip <ul><li>1. How many neutrons does Carbon-12 have? </li></ul><ul><ul><li>a. 2 </li></ul></ul><ul><ul><li>b. 6 </li></ul></ul><ul><ul><li>c. 12 </li></ul></ul><ul><ul><li>d. 18 </li></ul></ul><ul><li>2. In general, how does atomic mass vary throughout the periodic table? </li></ul><ul><ul><li>a. it is fixed and does not change as you move across the periodic table </li></ul></ul><ul><ul><li>b. it decreases from left to right, and from top to bottom </li></ul></ul><ul><ul><li>c. it increases from left to right, and from top to bottom </li></ul></ul><ul><ul><li>d. it increases from right to left, and from top to bottom </li></ul></ul>
  19. 19. Exit Slip <ul><li>3. Which of the following is true for isotopes? </li></ul><ul><ul><li>a. they change the identity of an atom to a different element </li></ul></ul><ul><ul><li>b. they have varying atomic numbers </li></ul></ul><ul><ul><li>c. they have varying atomic masses </li></ul></ul><ul><ul><li>d. they have varying numbers of electrons </li></ul></ul><ul><li>4. Why are atomic masses listed as decimals on the periodic table instead of whole numbers? </li></ul><ul><ul><li>a. they are a weighted average of the naturally occurring isotopes </li></ul></ul><ul><ul><li>b. their units are grams/moles </li></ul></ul><ul><ul><li>c. they were measured with a balance that read to only two decimal places </li></ul></ul><ul><ul><li>d. none of the above </li></ul></ul>
  20. 20. Exit Slip <ul><li>5. On the periodic table, why is Co (Cobalt) placed before Ni (Nickel) even though Ni has a higher atomic mass? </li></ul><ul><ul><li>a. Nickel has one more proton </li></ul></ul><ul><ul><li>b. Cobalt has fewer electrons </li></ul></ul><ul><ul><li>c. Nickel has a few more electrons </li></ul></ul><ul><ul><li>d. Cobalt has a lower density </li></ul></ul>
  21. 21. Homework <ul><li>Finish Practice Questions </li></ul><ul><li>Finish Foldable </li></ul><ul><li>Textbook: </li></ul><ul><ul><li>Pg. 86 Practice: #1, 2, 4 </li></ul></ul><ul><ul><li>Pg. 89 Section Review: #2, 4, 6, 8 </li></ul></ul>

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