Properties of Water

What makes water so special? 1

Properties of Water Polar Cohesion Surface Tension Adhesion Capillary Action High: Specific Heat/ Heat of Vaporization/ Heat of Fusion Less Dense as a Solid Universal Solvent 1

Chemistry of Water Different water molecules interact b/c oxygen is so electronegative that it “hogs” the electrons Making the oxygen end electronegative & the hydrogen sides electropositive

Water is Polar Oxygen has a partial (-) charge Hydrogen has a partial (+) charge Causes water to be POLAR, like a magnet

Chemistry of Water 2H + O  H2O Polar covalent bonds Hold a water molecule together

Covalent Bond vs. Hydrogen Bond VIDEO

Cohesion Water molecules attracted to each other creating surface tension 1

Surface Tension The tightness across the surface of water caused by cohesion Makes the surface act like a solid 1

Adhesion Water molecules are attracted to other substances such as glass, soil, and plant tissues 1

Water has strong adhesion Molecules stick to other molecules (of like polarity) Water “sticks” to other hydrophilic (water loving) substances

Capillary Action VIDEO Ability of water to “climb” up against gravity Results from Cohesion + Adhesion EX: Water moving up the roots to the top of the tree VIDEO 1

High Specific Heat Amount of heat (energy) required to raise the temperature of water by 1⁰ C VIDEO WATER = 75°F BEACH = 200°F 1

Water can absorb & store a huge amount of heat from the sun At night and during winter, the gradual cooling water can warm the air. Coastal regions – generally have milder climates

Therefore, water is a very stable medium It takes lots of energy (heat) to change the temperature of water (b/c have to break the hydrogen bonds first) It is Favorable for marine life

Also, because organisms are made primarily of water, they are more able to resist changes in their own temperatures

High Heat of Vaporization Hydrogen bonds must be broken before water can transition from a liquid phase to a gaseous phase (water vapor)

Water is Less Dense as a Solid Water in a liquid state keeps rebonding and changing its shape Water in a solid states has a fixed shape (crystalline lattice) with space in between making it less dense VIDEO 1

High Heat of Fusion *Ice forms from the top down *It is an Insulator in our oceans.

Frozen water takes on a crystalline lattice shape with pockets in between the molecules and so it floats in liquid water!

High Heat of Fusion Amount of energy it takes to turn a liquid into a solid. For water, it takes 80cal to turn 1 gram of water into ice Water is one of the few substances that are less dense as a solid than as a liquid. While other materials contract when they solidify, water expands. The cause of this exotic behavior is, once again, hydrogen bonding. At temperatures above 4º C, water behaves like other liquids, expanding as it warms and contracting as it cools. Water begins to freeze when its molecules are no longer moving vigorously enough to break their hydrogen bonds. As the temperature reaches 0º C, the water becomes locked into a crystalline lattice, each water molecule bonded to the maximum of four partners. The hydrogen bonds keep the molecules far enough apart to make ice about 10% less dense than liquid water at 4º C. When ice absorbs enough heat for its temperature to increase to above 0º C, hydrogen bonds between molecules are disrupted. As the crystal collapses, the ice melts, and molecules are free to slip closer together. Water reaches it greatest density at 4º C and then begins to expand as the molecules move faster.

Universal Solvent Water is a universal solvent because it dissolves more substances than any other liquid 1

It Dissolves both *Ionic compounds *Polar molecules b/c water is polar, it bonds to ions & polar molecules It Dissolves both *Ionic compounds *Polar molecules