1. The Science of Water

2. Why is water Essential? Necessary for life
Water in our atmosphere helps to keep the planet warm.
Our bodies are composed of ~70% dependent on water
Although a person can live without food for more than a month, a person can only live without water for approximately one week.
Your brain is 75-85% water and plays a vital role in your body's response to dehydration. It controls water intake through altering thirst and varying the water excretion from your kidneys.

3. Why study water?
The chemical reactions of all living things take place in an aqueous (water based) environment. Thus, water is one of the most important compounds found in living things!

4. Forming a Water Molecule
Water (chemical formula H2O) has 2 hydrogen atoms and 1 oxygen atom. Bohr model for water: 8P 8N 1P 0N

5. Water is POLAR covalent
Recall that electrons are SHARED in a covalent bond.
Polar= electrons are shared unevenly
Oxygen’s 8 p+ attract e- more strongly than Hydrogen’s 1 p+ (more electronegative)
O pulls on e- more electrons more likely to be found near Oxygen)

6. Electronegativity?!
The attraction of an atom for the electrons of a covalent bond
Tendency for an atom to pull electrons toward itself
2 atoms of the same element have equal electronegativities
 Share electrons equally in a covalent bond, forming a nonpolar covalent bond.

7. Water is POLAR covalent
What does it mean?
Water has a partial + pole & a partial – pole (called dipole)
Acts like a magnet

8. So what? Hydrogen Bonds!
Opposites Attract! Partial + of 1 water molecule will attract and stick next to partial – of another molecule
Called a Hydrogen Bond
NOT real bonds, just an attraction
 “weak bond” that are easily broken

10. Who Cares?! Hydrogen bonds give water its special properties!!!

11. Properties of Water Adhesion & Cohesion High Specific Heat
Solid ice is less dense than liquid water
Universal Solvent

12. Cohesion Attraction between molecules of the same substance
Reason water creates beads
Penny experiment!
Responsible for water’s high surface tension
A measure of how difficult it is to stretch or break the surface of a liquid
Water is very cohesive because one water molecule may form as many as 4 hydrogen bonds at the same time.
Jesus Christ Lizard

13. Adhesion Attraction between molecules of different substances
Explains why microscope slides stuck together
Measuring volume in graduated cylinder?

14. Cohesion + Adhesion
Capillary action in plants
Water in Space

15. High Specific Heat
Specific Heat is the amount of heat energy required to increase the temperature of water.
Water’s multiple hydrogen bonds between its molecules gives it a very high specific heat
Absorbs large amounts of heat energy with only small changes in temperature
Releases heat energy slowly
Moderates the Earth’s climate and helps living organisms regulate their body temperature

16. Ice is Less Dense than Water
Density of H2O at different temperatures
Temperature (°C)
Density (g/cm3)
0 (solid)
0.9150
0 (liquid)
0.9999 4
1.0000 20
0.9982
100 (gas)
0.0006

17. Ice is Less Dense than Water
This is a very rare property!
Why is it important that ice floats?
Floating ice insulates the water
beneath it and prevents it from
freezing.
Allows aquatic organisms that
live in water to survive during
cold weather.

18. Ice Melting
Ice (left) has an open lattice structure due to permanent hydrogen bonds that collapse when it melts. In liquid water (right), molecules are connected by short-lived hydrogen bonds because water is fluid.
ICE WATER

19. Water is a Universal Solvent
The polarity of water allows nearly any polar (unequal distribution of charges) substance to be dissolved in water
Water can dissolve more substances than any other liquid.
Solution = liquid consisting of uniform mixture of two or more substances
Two parts of a solution:
Solvent = liquid (dissolving agent)
Solute = substance dissolved
Example:
Water = solvent Koolaid powder/sugar = solutes Kool-aid = solution

20. Rule to Making Solutions
“Like Dissolves Like”
DO NOT CONFUSE WITH OPPOSITES ATTRACT
Since water is polar, it will dissolve ions and other polar substances
ex: Salt (NaCl)  breaks down into Na+ and Cl- ions
Hydrophilic = water loving. Dissolves in water.

21. Nonpolar molecules Water will not dissolve nonpolar molecules
Hydrophobic = afraid of water. Does not dissolve in water.
Electrons are shared equally in nonpolar molecules.
 Does not form Hydrogen Bonds
Oil is an example of a nonpolar molecule.

22. Solid, Liquid, and Gas
Water is the only substance which exists under normal conditions on earth as a solid, a liquid, and a gas.

23. High Boiling Point
Water’s high boiling point, allows water to remain as a liquid over most of Earth’s surface
Crucial to life as almost all organisms need liquid water to survive.