6. Which is more important in determining the chemical behavior of an atom, the number of neutrons or the number of protons? Why?

7. What holds two hydrogen atoms together in a molecule? Why do two helium atoms not form a stable molecule?

8. Why do two hydrogen atoms become more stable if they are brought together, but then become less stable again if they are brought too close?

9. How is the molecular weight of a molecule related to the atomic weights of the atoms from which it is made?

10. What is a mole of a chemical substance? How is the mole concept useful in chemistry?

11. How many molecules are present in one mole of water vapor? Of liquid water? Of ethyl alcohol?

12. What is the molecular explanation for the phenomenon of pressure?