What makes water so special?

Physical properties Is clear, colorless, odorless, and tasteless * Colors, tastes and odors are caused by substances dissolved in the water. Boils at 100°C Freezes at 0°C Density = 1.0 g/mL (at 4°C)

Water A water molecule (H2O), is made up of three atoms --- one oxygen and two hydrogen. H O 1

Atom review

Bonding review Animations on atomic bonding

The bond between water ATOMS are Covalent Bonds

So…what makes water so special?

Water is Polar!!!! Molecules can be grouped as polar or non-polar molecules. Some molecules are in between the two. A polar molecule has a partial positive charge in one part of the molecule and complementary negative charge in another part.

The oxygen end “acts” negative The hydrogen end “acts” positive Causes the water to be POLAR, like a magnet.

Non Polar Molecules A non-polar molecule is one in which the electrons are distributed more symmetrically and thus does not have an abundance of charges at the opposite sides. The charges all cancel out each other.

Hydrogen Bonds Exist Between Water Molecules Formed between a highly Electronegative atom (like oxygen in another water) of a polar molecule and a hydrogen Weak bond, but strong in great numbers

Hydrogen bonds are responsible for five important properties of water 1

Properties of Water Cohesion Adhesion High Specific Heat High Heat of Vaporization Less Dense as a Solid 1

Cohesion is the attraction among molecules of a substance Cohesion is the attraction among molecules of a substance. In other words, water is “sticking” to other water molecules due to hydrogen bonds. ( why water is attracted to itself) Fig. Water’s surface tension comes from hydrogen bond’s that cause water molecules to stick together.

Cohesion Results in surface tension (a measure of the strength of water’s surface) 1

Helps insects walk across water Cohesion … Helps insects walk across water

Universal solvent (adhesion) – the attraction among molecules of different substances is called adhesion. In other words, water is “sticky” to lots of other substances. transpiration Example: Adhesion helps plants transport water from their roots to their leaves because water sticks to the sides of cellular structures in plants called xylem.

Adhesion Attraction between two different substances. Water will make hydrogen bonds with other surfaces such as glass, soil, plant tissues, and cotton. Capillary action-water molecules will “tow” each other along when in a thin glass tube. 1

Adhesion Causes Capillary Action Which gives water the ability to “climb” structures water molecules will “tow” each other along when in a thin glass tube.

High Specific Heat Amount of heat needed to raise or lower 1g of a substance 1° C. Water resists temperature change, both for heating and cooling. Would you rather walk on sand or in water on a beach on a hot summer day? Which would be warmer that night? Why? 1

High Heat of Vaporization Water in its liquid form has an unusually high boiling point temperature, a value close to 100°C. As a result of the network of hydrogen bonding present between water molecules, a high input of energy is required to transform one gram of liquid water into water vapor, 1

Water is Less Dense as a Solid Which is ice and which is water? 1

Water is Less Dense as a Solid Water is less dense as a solid due to its hydrogen bonds.

Water is the solvent, salt is the solute salt water is the solution Solutions Water is the solvent, salt is the solute  salt water is the solution

Acids, Bases and pH H2O  H+ + OH- One water molecule is made of two ions, (H+) and a Hydroxide Ion (OH-) Hydrogen Ion Hydroxide Ion Acid Base H2O  H+ + OH-

Acids and Bases Acid: A solution with lots of H+ ions pH 0 up to 7 is acid (acidic) Base: A solution with lots of OH- ions pH above 7 – 14 is basic (alkaline)

The pH Scale Indicates the percent of H+ ions Ranges from 0 – 14 pH of 7 is neutral