1. Ch. 2 Pre-AP Biology Ms. Haut
Properties of Water
Ch. 2
Pre-AP Biology
Ms. Haut

2. Properties of Water Cohesive nature of water
Ability to moderate temperature
Unusual phase changes
Versatile solvent

3. THE PROPERTIES OF WATER
1. Cohesion of Water
Water is a polar molecule, electrons are shared unequally
Cohesion is the ability of water molecules to attach to other water molecules
Attach by hydrogen bonds
Modified from PowerPoint lectures

4. In a water molecule, oxygen exerts a stronger pull on the shared electrons than hydrogen
This makes the oxygen end of the molecule slightly negatively charged
The hydrogen end of the molecule is slightly positively charged
Water is therefore a polar molecule
(–)
(–) O H H
(+)
(+)
Figure 2.9
Modified from PowerPoint lectures

5. H+ atom is covalently bonded to the oxygen via a shared pair of electrons.
Oxygen is an "electronegative" or electron "loving" atom compared with hydrogen
"polar" molecule, meaning that there is an uneven distribution of electron density
This attraction forms weak bonds called hydrogen bonds

6. Hydrogen bonds make water Cohesive
The oxygen end of water has a negative charge and the hydrogen end has a positive charge.
The hydrogens of one water molecule are attracted to the oxygen from other water molecule. This forms Hydrogen Bonds.
Cohesion = the ability of water molecules to stick to other water molecules

7. Surface Tension
Surface tension is the name we give to the cohesion of water molecules at the surface of a body of water

8. Due to hydrogen bonding, water molecules can move from a plant’s roots to its leaves
Insects can walk on water due to surface tension created by cohesive water molecules
Water Strider
Figure 2.11
Modified from PowerPoint lectures

9. Adhesion
Water can also be attracted to other materials.

10. Capillary Action Water molecules are attracted to the straw molecules.
When one water molecule moves closer to the straw molecules the other water molecules (which are cohesively attracted to that water molecule) also move up into the straw.

11. Giant Redwoods—Muir Woods, CA
Plant Transpiration—aided by cohesion and adhesion

12. Water’s hydrogen bonds moderate temperature
It takes a lot of energy to disrupt hydrogen bonds
Therefore water is able to absorb a great deal of heat energy without a large increase in temperature
As water cools, a slight drop in temperature releases a large amount of heat
Yankicha Island Boiling Water
Modified from PowerPoint lectures

13. Water has a high Specific Heat
Specific heat = heat needed to raise temp. of 1g of substance by 1ºC
Specific heat of water is very high
Boiling Point High .... water stays liquid longer
As such, water can act as heat reservoire, moderating Earth’s global temperature

14. This leads to evaporative cooling
A water molecule takes a large amount of energy with it when it evaporates
This leads to evaporative cooling
Figure 2.12
Modified from PowerPoint lectures

15. Unusual Phase Change
Like no other common substance, water exists in nature in all three physical states:
as a liquid
as a gas
as a solid
Figure 2.10B
Modified from PowerPoint lectures

16. Water in three different states
Figure 2.10Bx

17. States of Water

18. Gas
Liquid
Solid

19. Ice, molecular model Figure 2.13x3
Modified from PowerPoint lectures

20. Water, molecular model Figure 2.13x4
Modified from PowerPoint lectures

21. Hydrogen bonds are stable Hydrogen bonds constantly break and re-form
Density of Water
Ice is Less Dense than Liquid Water
Molecules in ice are farther apart than those in liquid water
Water is densest at 4°C.
Figure 2.13
Hydrogen bond
ICE
Hydrogen bonds are stable
LIQUID WATER
Hydrogen bonds constantly break and re-form
Modified from PowerPoint lectures

22. Frozen water floats (left) and frozen benzene sinks (right)
Figure 2.13x2
Modified from PowerPoint lectures

23. Ice fishing
Figure 2.13x1
Modified from PowerPoint lectures

24. Water is a Versatile Solvent
Also known as the “Universal solvent”.
Polar substances are enveloped by hydration spheres.
“Like dissolves like!”

25. Solutes whose charges or polarity allow them to stick to water molecules dissolve in water
They form aqueous solutions
Na+ – –
Na+ + +
Cl–
Cl– – – + + –
Ions in solution
Salt crystal
Figure 2.14
Modified from PowerPoint lectures

26. Acknowledgements
Unless otherwise noted, illustrations are credited to Pearson Education have been borrowed from BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003. These images have been produced from the originals by permission of the publisher. These illustrations may not be reproduced in any format for any purpose without express written permission from the publisher.