7. Figure 2-3 The highlighted elements are the most abundant elements found in organisms Number of unpaired electrons = valence, also # of bonds that could be created.

13. Molecular Representations Methane Ammonia Water Oxygen Molecular formulas: Structural formulas: Ball-and-stick models: Space-filling models:

15. Water Molecules and Hydrogen Bonding Water is polar. Hydrogen bonds form between water molecules. Electrons are pulled toward oxygen

16. Structure of Water: Liquid and Ice In ice, water molecules form a crystal lattice. In liquid water, no crystal lattice forms. Liquid water is denser than ice. As a result, ice floats.

17. Structure of Water: Liquid and Ice In liquid water, no crystal lattice forms.