WATER

The Importance of Water It is the most abundant liquid on earth (___ of the earth’s surface is covered by water) ___________ of living tissue is made up by water If you weigh 145 pounds ______ lbs of that is water 3/4 50 to 90 % 100

Polar Covalent Molecules    Water has a special type of bond called a _________________________ bond. Because the electrons spend more time surrounding the ___________ atom, the oxygen has a net ____________ charge, and the hydrogens have a net ____________ charge. POLAR COVALENT Oxygen negative positive See p.13-14 Biochemistry CD

Therefore this molecule is _________. POLAR

Two polar molecules will attract to each other by their polar charges and therefore form a _____________. LATTICE

Hydrogen Bonds Water molecules are joined together by _______________. The hydrogen bonds are ________, however, there are so many of them in a water lattice, that collectively they are very ________. weak strong This is important, as they make water ___________. very stable

why does ice float on water? Icebergs float because water expands and becomes less dense as it freezes. Most things get smaller as they cool but water actually gets bigger because the ice water molecules take up more space than liquid water molecules. Cool water molecules form strong hydrogen bonds that push the water molecules into patterns that hold them apart from each other. Water expands and becomes less dense as it freezes

Properties of Water #1 SURFACE TENSION The cohesion of water molecules. They “stick together”. https://www.youtube.com/watch?v=RphuMEUY3Og

#2 CAPILLARY ACTION Water is sucked up a small tube against the force of gravity because: Molecules stick together (cohesion) Molecules stick to the outer surface (adhesion) See p.27 Biochemistry CD

#3 HEAT OF VAPORIZATION A lot of ENERGY is needed to break a water lattice apart (liquid to gas). Therefore, water is stable over a wide range (0 to 100oC) See p.24 Biochemistry CD

#4 SOLVENT PROPERTIES Water can dissolve any IONIC compound. WHY? The polarity of water will break the bonds between ionic compounds. + & - attract! See p.25-26 Biochemistry CD

water with ionic compounds HYDROPHYLIC: any compound that dissolves in water. Usually IONIC compounds. water with ionic compounds

WATER NOT DISSOLVING OIL HYDROPHOBIC: any compound that will NOT dissolve in water. Usually COVALENT compounds. water with covalent compounds WATER NOT DISSOLVING OIL

#5 H2O H+ and OH- IONIZATION OF WATER When the attraction is greater for something else (ie: an ionic compound), the hydrogen bonds will break and tear water molecules apart. This causes the oxygen and hydrogen to dissociate into ions (H+ and O-). H2O H+ and OH-