1. Water Notes

2. Biology, 9th ed,Sylvia Mader
Chapter 02
Water Molecule
Water is a POLAR molecule
The oxygen atom “pulls” on electrons more than the hydrogen atoms.
Because of this, oxygen has a slight negative charge and the hydrogens have a slight positive charge.
Basic Chemistry

3. Because it is polar, it forms HYDROGEN BONDS
Oxygen attracts the shared
electrons and is partially negative.
Hydrogens are partially positive.
Ball-and-stick Model
Electron Model
Space-filling Model
hydrogen
bond
a. Water (H2O)
b. Hydrogen bonding between water molecules O
104.5°
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Separate water molecules form temporary and brief bonds with nearby water molecules.
The H of one molecule is attracted to the O from another

4. Properties of Water 1 and 2: Cohesion & Adhesion
Biology, 9th ed,Sylvia Mader
Chapter 02
Properties of Water 1 and 2: Cohesion & Adhesion
Cohesion:
Hydrogen bonds hold water molecules tightly together
i.e. allows water to flow freely without molecules separating.
Adhesion:
Hydrogen bonds for between water and other polar materials
Allow water be drawn many meters up a tree in a tubular vessel
Basic Chemistry

5. Property 3: High Surface Tension
Water molecules at surface hold more tightly than below surface
Amounts to an invisible “skin” on water surface
Allows small nonpolar objects (like water strider) to sit on top of water

6. Property 4: Capillary Action
Biology, 9th ed,Sylvia Mader
Chapter 02
Property 4: Capillary Action
Water evaporates, pulling the water
column from the roots to the leaves.
Water molecules cling together and
adhere to sides of vessels in stems.
Water enters a plant at root cells.
H2O
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Because of cohesion and adhesion, water has the ability to move through narrow spaces.
This is why water seeps through a paper towel, and how it moves against gravity to the tops of trees
Basic Chemistry

7. Property 5: Ice is less dense than water
Biology, 9th ed,Sylvia Mader
Chapter 02 4
100
1.0
0.9
Density (g/cm3)
Temperature (ºC)
liquid water
ice lattice
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Property 5: Ice is less dense than water
Frozen water less dense than liquid water
Otherwise, oceans and deep lakes would fill with ice from the bottom up
Ice acts as an insulator on top of a frozen body of water
Melting ice draws heat from the environment
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ice layer
Protists provide
food for fish.
River otters visit
ice-covered ponds.
Aquatic insects survive
in air pockets.
Freshwater
fish take
oxygen
from water.
Common frogs and pond turtles hibernate.
Basic Chemistry

8. Biology, 9th ed,Sylvia Mader
Chapter 02
Water: pH Scale
pH value
10–1
10–2
10–3
10–4
10–5
10–6
10–7
10–8
10–9
10–10
10–11
10–12
10–13
10–14
10 0
Examples
hydrochloric acid
acidic
basic
stomach acid, lemon
juice
vinegar, cola, beer
tomatoes
black coffee
urine
pure water
seawater
baking soda
Great Salt Lake
household ammonia
household bleach
sodium hydroxide 1 2 3 4 5 6 7 8 9 10 11 12 13 14
H+ Ion
Concentration
Used to indicate acidic or basic a solution is
Values range from 0-14
0 to <7 = Acidic
7 = Neutral
>7 to 14 = Basic (or alkaline)
Acids are usually sour to taste, bases are bitter.
Basic Chemistry