Inquiry in the Natural World – Fall 2002              Guide for Topic 6:  What are atoms? etc.

 

Topic Objectives:

 

1)  Understand the Atomic Theory of Dalton, its strengths in the early 1800s, and its limitations for current use. 

      Recognize an application of Dalton’s ideas within a (given) simple chemical scenario.

 

      2)  Know how the Periodic Table evolved (Dobereiner, Newlands, Mendeleev, Meyer).

 

3)  Understand how Rutherford’s gold-foil experiment led to a rudimentary understanding of the atom.

 

4)  Understand the atom as a combination of the three primary types of subatomic particles:  proton, neutron, electron. 

     

      5)  Understand the organization of the modern Periodic Table (atomic number, rows vs. groups).  Know that the Table can be used to predict an element’s chemical reactivity (ionic bonding, covalent bonding, tendency not to bond). 

 

      6)  Know the relationships that exist between atomic number, atomic mass (called “mass number” in T/H), and the

             number of protons, electrons, and neutrons in an atom.

 

7)  Know the following names/vocabulary in addition to the names/terms mentioned above:  Bunsen and Kirchhoff;

      compound, molecule, nucleus, ion, electron shell (or electron energy level),        valence (or outer-shell) electrons,

      isotope, chemical reaction, chemical bond (ionic, covalent).

 

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Reading Assignments for Friday, October 4:

                     

 1)  M. D. Joesten and J. L. Wood, World of Chemistry, 2^nd Ed., Saunders, 1996, p. 48-58, espec. p. 48-53 and 57-58.

 2)  For a less connected discussion of some of the same info as Ref.1, see:  J. Trefil and R. M. Hazen, The Sciences,

        Ch. 8, p. 172-180; Ch. 10, p. 211-216 (skip “metallic bond”); Ch. 12, p. 261-263.

 

 

Discussion Topics / Active Learning Exercises for Friday, October 4:

 

1)   What previous ideas of Lavoisier and Proust were able to be explained using Dalton’s Atomic Theory?

 

2)   Explain how Dalton’s Atomic Theory can be used to support or disprove the following claims:

       a) The hydrogen atoms in one water molecule (H-O-H) contribute the same amount of mass as the hydrogen atoms

              in another water molecule.

       b) Hydrogen peroxide (H-O-O-H) and water (H-O-H) are different compounds.

       c) If the compound “CO” exists, then a compound with the formula “CO₂” cannot possibly exist.

 

3)   a) Describe the setup and the experimental results of Rutherford’s gold foil experiment.

      b) Think up several simple models of the atom that would be definitively ruled out by these results.

      c) Based on his results, what conclusions did Rutherford reach concerning the gold atoms?

 

4)  Marie Sklodowska Curie discovered the radioactive element polonium in 1898.  Its chemical symbol is Po, and its atomic number is 84.  Several isotopes were discovered.

      a) Po-209, the polonium isotope that can exist for the longest time, has an atomic mass of 209 mass units. 

           How many protons, neutrons, and electrons does Po-209 have? 

      b) Po-212 is a polonium isotope with atomic mass of 212.  Exactly how does Po-212 differ from Po-209?

 

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Reading Assignments for Monday, October 7: 

       

  1)  B.W. Tillery, E.D. Enger, and F.C. Ross, Integrated Science, McGraw-Hill, 2001, p. 242-249 and 256.  

  2)  Also see:  J. Trefil and R. M. Hazen, The Sciences, Ch. 8, 188-190.

 

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Discussion Topics / Active Learning Exercises for Monday, October 7:

 

1)  The following questions relate to Mendeleev’s original development of the Periodic Table:

        a) Which properties of elements did Mendeleev use to select the members of vertical columns

            (also called families or groups)?

        b) Which property of elements did Mendeleev use to organize elements in a horizontal row (period)?

             NOTE: today we use atomic number, which was discovered long after Mendeleev’s work.

        c) Which property was the most important for ordering?

  d) How did the lack of good data hinder the development of the periodic table?

  e) How do we know that we have found all of the first 92 elements?

 

2)  In pairs or groups, you will also do a short exercise on identifying some missing elements from the modern Periodic

      Table.  (You will not get the exercise before Monday’s class).  You will have to make sense of trends in

      reactivity as well as physical trends within the rows and periods – see examples on Tillery p. 242-4

                                       

3)  (OPTIONAL – at discretion of instructor)

     As stated on Trefil/Hazen p. 212, “Most atoms adopt one of three simple strategies to achieve a filled shell (that is, an

     electron arrangement of 2, 10, 18, 36, etc., electrons).”

      a) What are these three ways that atoms can get a filled shell of electrons?

      b) Which atoms already have a filled shell in their natural state?

      c) Identify which ways of achieving a filled shell are necessary in the following chemical transformations:

             i.  A sodium atom (Na) reacts with a chlorine atom (Cl) to yield sodium chloride. 

                  Sodium chloride is a salt made of positive sodium ions and negative chlorine ions.

            ii.  A carbon atom (C) reacts with four fluorine atoms (F) to yield carbon tetrafluoride (CF₄). 

                        NOTE:  CF₄ is not made of ions.