Properties of Water

Structure of a Water Molecule What keeps a water molecule together? Polar Covalent bond What is a polar bond? Unequal sharing of electrons. What is a Covalent Bond? A bond in which electrons are shared. The bonds within one molecule are called intramolecular bonds. H20

Polarity and Water Molecule Water is Polar. Polar substances charge is neutral, but one end of the molecule is positive and the other end is negative. Non-polar substances, like fats, will NOT dissolve in water. These substances are neutral and there is no excess charge at one end of the molecule. A basic rule is: Like dissolves in Like. This means that, in general, polar substances will dissolve in other polar substances, and that non-polar substances will dissolve in other non-polar substances. Polar substances will not dissolve non-polar substances.

Why does Oxygen attract electrons more than hydrogen? Electronegativity- is a measure of the ability of an atom in a chemical compound to attract electrons. Electro negativity depends on 2 factors 1.The number of protons in the nucleus. 2.The distance the electrons are from the nucleus.

HYDROGEN BONDS What is a hydrogen bond?  A chemical bond in which a hydrogen atom of one molecule is attracted to an electronegative atom, generally a nitrogen, oxygen, or flourine atom. The hydrogen of one water molecule bonds with the oxygen of another water molecule and so on. This is an example of intermolecular bonding. Each water molecule can form a maximum of 4 hydrogen bonds. They form, break, and reform with great frequency

What is Cohesion? The intermolecular attraction between like-molecules  Water has a greater surface tension than most other liquids.  Why do you think this is? hydrogen bonding  Some animals can stand, walk, or run on water without breaking the surface. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 3.3 Cohesion

Adhesion What is Adhesion? Attraction between two different substances. Water will make hydrogen bonds with other surfaces such as glass, soil, plant tissues, and cotton. Examples: transpiration process which plants and trees remove water from the soil, and paper towels soak up water.

Adhesion Also Causes Water to … Form spheres & hold onto plant leaves Attach to a silken spider web capillary action within a plant

Heat capacity In order to raise the temperature of water, the average molecular speed has to increase. It takes much more energy to raise the temperature of water compared to other solvents because hydrogen bonds hold the water molecules together! Water has a very high heat capacity As water evaporates, it removes a lot of heat with it.

Three-fourths of the earth is covered by water. The water serves as a large heat sink responsible for: 1.Prevention of temperature fluctuations that are outside the range suitable for life. 2.Coastal areas having a mild climate 3.A stable marine environment 4.Prevents organisms from over heating. Importance of high heat capacity

Water is Less Dense as a Solid Water is less dense Water is less dense as a solid than as a liquid (ice floats) Liquid water has hydrogen bonds that are constantly being broken and reformed. Frozen water forms a crystal-like lattice whereby molecules are set at fixed distances.

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

Why is density of water important? The density (mass over volume) of water: 1. Prevents water from freezing from the bottom up. 2. Ice forms on the surface first—the freezing of the water releases heat to the water below creating insulation. 3. Makes transition between season less abrupt.