III. Water A.Polarity 1.In some covalent bonds, electrons are attracted more strongly to one atom than another. 2.One end of the molecule will then be partially positive, & the other end will be partially negative. These molecules are polar. 3.Ex: water!

B.Hydrogen bonds (H-bonds) 1.When bonded to O 2, N 2, or F, a hydrogen has a partial positive charge nearly as great as a proton. 2.This hydrogen is then attracted to the negative region of polar molecules, forming hydrogen bonds.

C.Properties of Water – most result because water forms hydrogen bonds with itself 1.Ice Floats – solid water is less dense than liquid water (h-bonds) 2.Water absorbs & retains heat – large bodies of water keep Earth’s temp. regulated; water maintains organisms’ internal body temp.

3.Cohesion – h-bonds hold water molecules together 4.Adhesion – water sticks to other polar substances both cohesion and adhesion allow water to move upward through roots and stems of plants

D.Solutions – one or more substances mixed evenly in another substance (water) 1.Solute – substance that is dissolved (salt) 2.Solvent – substance that does the dissolving (water) 3.Concentration – every solution has a certain amount of solute per amount of solvent Conc. = solute (g) / solvent (mL) 4.Saturated Solution – solution that cannot hold any more solute 5.Aqueous Solution – solution in which the solvent is always water.

E.Acids & Bases 1.Dissociation – a molecule breaks into its ions H 2 O ↔ H + + OH - H + = hydronium ion OH - = hydroxide ion 2.Acid – solution with more hydronium ions HCl = hydrochloric acid 3.Base – solution with more hydroxide ions NaOH = sodium hydroxide

4.pH scale – measures the concentration of hydronium ions; is logarithmic, so each step is 10 times more acidic or basic pH of 0-6 is acidic pH of 7 is neutral pH of 8-14 is basic or alkaline o pH of 1 is 10 times more acidic than pH of 2 o pH of 14 is 100 times more basic than pH of 12 5.Buffers – chemicals that neutralize acids and bases; they prevent changes in pH