1. Give the number of valence electrons for each atom:  H, Be, O, Ne, Al.  (Use the periodic table given to you earlier in the semester).
2. If the following atoms could react to form ions, what would be the expected charge on each?  H, Be, O, Ne, Al
3. Oxygen's "desire" for a full shell of electrons is so great that it does not exist under normal conditions as individual oxygen atoms, but rather as O₂ molecules with a double bond between the two O atoms.  Explain how this bonding allows each oxygen atom to have a share of a full shell.
4. Find the elements in these compounds on the periodic table and then decide, based upon the element position in the table, whether they would more likely share electrons in covalent bonds or form ionic bonds:  LiBr, SO₂, N₂, K₂O, MgCl₂, NO₂
5. Why do sodium (atomic number = 11) and potassium (atomic number = 19) exhibit similar chemical behavior?
6. You have learned about the first law of thermodynamics, or the conservation of energy.  When an electron moves from a lower to a higher energy orbital (as when light strikes chlorophyll molecules) and from a high back down to a lower energy orbital, how is the energy conserved?
7. Like most molecular substances, water can exist as solid, liquid, or gas, depending on the pressure and temperature conditions.  Consider the description of how molecules behave in each state.  In which state is entropy greatest and in which lowest?
8. If you pour rubbing alcohol on your hand, it will evaporate and your hand will feel cold.  Why does your hand get cold?  Where is the heat going?
9. Draw the methane molecules (CH₄).  (a)  What types of bonds exist between the hydrogens and carbon?  (b)  Is methane a polar or nonpolar molecule?  Why?
10. Water striders and some other organisms are able to "walk on water".  Explain the chemistry of water that makes this possible.
11. What happens to water molecules to cause water to form ice at low temperatures?  Why is ice less dense than liquid water?

[Adapted from Trefil, J. and R. M. Hazen.  1995.  Instructor's Manual.  The Sciences: An Integrated Approach.  John Wiley & Sons., Inc.]