Answers to UNIT 2 Self Test:

Part 1: Multiple Choice with explanation.

1.  c: The electron is the lightest, then proton, then hydrogen, which contains an electron and proton, lastly Helium which contains 2 protons, 2 neutrons and 2 electrons.

2.  a: atomic number = # of protons (and # of electrons in atom), mass number = # of protons and # of neutrons added.

3.  c: format dictates that the mass number (protons + neutrons) is written in the upper left of the symbol and the atomic number (# of protons) is written in the lower left of the symbol.

4.  c: The 3rd energy level contains 9 orbitals, each of which can contain two electrons making 18 electrons possible in the 3rd energy level. (n=3, so 2n² = electrons per energy level, n.)

5.  a: Hund's rule reminds us that by spreading out electrons with parallel spin into separate orbitals with equal energy minimizes the overall electronic energy of the configuration.

6.  Dalton's atomic theory: (1) Each element is composed of tiny indivisible atoms.  (2) All atoms of a given element are identical to each other and different from those of any other element.  (3) Atoms are neither created nor destroyed in any chemical reaction.  (4) A given compound always has the same relative numbers and kinds of atoms.

7.    Thomson -- cathode ray tube -- plum pudding model (chocolate chip cookie dough)
        Rutherford -- gold foil experiment -- nuclear model
        Bohr -- atomic spectrum tube -- planetary model

8.  (a)  ²³⁸U  -->  ⁴He  +  ²³⁴Th
              ^{92            2             90}

(b)  ³⁸Cl  -->  ⁰b  +  ³⁸Ar.
       ^{17            -1          18}  

9.    Complete the following nuclear equations.

¹⁸⁵Au  -->  ¹⁸¹Ir  +  ⁴He
 <sup>79                77          2

1</sup>n  +  ²³⁵U  ---->  ¹⁴¹Ba  +  ⁹²Kr  +  3 ¹n
^{0          92                 56            36              0}

10.  a. 1s² 2s² 2p⁶ 3s² 3p⁴
       b. [Kr] 5s² 4d²
       c.  1s² 2s² 2p⁶ 3s² 3p⁶ 

11.  a.  hi  hi  h     
              1s         2s                  2p 

        b.  hi  hi  h  h  h 
              1s         2s                  2p             

         c.  [Ar]  hi  hi h h h h
                        4s                      3d

12.  a. 3p    b. 4d    c. 3d        13. a. 2    b. 2    c. 6        14. a. Mg    b. P    c. Cu    d. Mn