We’ve met and discovered many organisms that have surprised us in their abilities to survive and even thrive in many harsh and inhospitable environments.
Mars video

Due to the unequal sharing of electrons in a covalent bond

Hydrogen bonding…
Leading to the property of cohesion
(the attraction among like molecules)

How difficult it is to stretch or break the surface of a liquid.

Water is not the only substance with charged regions, so the charged areas of the water molecule can be attracted to oppositely charged areas on other types of molecules resulting in adhesion …the attraction of unlike molecules.

The combined effects of cohesion and adhesion
Water conducting cells
100 µ m Figure 3.3

Heat
Is a measure of the total amount of kinetic energy of the molecules
Temperature
Measures the average speed of one molecule of the substance.
Think of a cool swimming pool vs a hot cup of tea.
Which has the higher temperature?
Which has more heat energy?

The specific heat of a substance:
The amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1’C.

Water has an extremely high specific heat, which allows it to minimize temperature fluctuations on the Earth and in your body.
The specific heat of water is 1 cal/g ‘C
So…
A calorie is the amount of heat required to raise
1g of water by 1’C.
A kilocalorie (kcal, or Calorie) is the amount of heat required to raise 1kg of water by 1’C.

Have you ever gone in the ocean on a nice, hot day in early June?
What about a mildly cool day in mid-
September?
Most deserts are extremely hot during the day, but what happens when the sun goes down?

Water moderates air temperature by absorbing heat from air that is warmer and releasing the stored heat to air that is cooler.
The Gulf Stream redistributes the heat energy from the equator to the higher latitudes of
Western Europe.

A similar thing happens when you perspire…each droplet of sweat contains a large amount of heat energy that is sent to the surface of your body to be released to the air around you as it turns to a gas. You warm up the air when you sweat!

In order for one gram of liquid water to turn into a gas at room temp, 580 calories of heat energy must be absorbed. Again, water has a very high heat of vaporization compared to most other substances.
Remember…breaking bonds releases energy (exergonic) and forming bonds requires energy (endergonic).

Ice is less dense than liquid water and therefore floats on it. It serves to insulate the water below the ice. (Ponds are not frozen to the bottom!...life continues all winter).
To form the crystal lattice, water molecules “push away” from each other.
Figure 3.5
Hydrogen bond
Ice
Hydrogen bonds are stable
Liquid water
Hydrogen bonds constantly break and re-form

Because water is polar it can dissolve most charged solutes and ionic compounds.

Figure 3.6
Negative oxygen regions of polar water molecules are attracted to sodium cations (Na + ).
Positive hydrogen regions of water molecules cling to chloride anions
(Cl – ).
Cl
–
Na +
–
+
+
–
–
+
–
–
Na +
Cl
–
–
–
+
–
+
+
+
–
–
+

 –
This oxygen is attracted to a slight positive charge on the lysozyme molecule.

+
This hydrogen is attracted to a slight negative charge on the lysozyme molecule .
Figure 3.7
(a) Lysozyme molecule in a nonaqueous environment
(b) Lysozyme molecule (purple) in an aqueous environment such as tears or saliva
(c) Ionic and polar regions on the protein’s
Surface attract water molecules.

Hydrophilic ; “water-loving” polar or ionic substances carbohydrates, proteins, ionic compounds
Hydrophobic ; “water-fearing” non-polar substances fats, oils, lipids

So what if I need to dissolve a non-polar compound?
Use a non-polar solvent.
Remember the rule “Like dissolves like”.

A mole
Represents an exact number of molecules of a substance in a given mass
How many moles are there in 20 grams of hydrogen?
H’s atomic mass ~ 1
Moles = mass/relative mass = 20/1 = 20 moles.
Molarity
Is the number of moles of solute per liter of solution
Measures concentration

Water dissociates into hydronium and hydroxide ions
Figure on p. 34 of water dissociating
H
H
H
H
H
+
H
H
+
Hydronium ion (H
3
O + )
–
H
Hydroxide ion (OH
–
)

Acids; increase hydrogen ion concentration
Bases; decrease hydrogen ion concentration (increase hydroxide ion concentration)

Remember that pH is based on the negative log of the concentration of hydrogen ions, so a higher pH number is a lower concentration of ions.

The internal pH of most cells is 7
Human blood is about 7.4
Buffers are substances that minimize changes in the concentrations of hydrogen and hydroxide ions in a solution
They consist of an acid-base pair that either donates or accepts hydrogen ions in reversible reactions.
Living things make the buffers they need to maintain homeostasis.