Description
Covalent Bonds
Polar covalent bond electrons not equally shared between molecules
Cohesiveness of Water
o Cohesion also means that water has a high surface tension
o this is why it hurts to belly flop, because all these weak hydrogen bonds together make a strong surface
o water moderates changes in temperature
o water has an unusually high specific heat
o amount of energy required to change 1g of water by 1 degree Celsius
Because of the hydrogen bonds:
o Water has a high heat of vaporization
o As a liquid evaporates, its remaining surface cools, a process called evaporative cooling
We also discuss several other topics like What is the formula for molality?
o This is why we sweat, as the water evaporates, the water takes with it heat from the core
Water is most dense at 4 degrees Celsius, not Zero
o Frozen water floats on liquid water; the water Is most dense just above freezing point
o Hydrogen bonds stabilize at 0 degrees and molecules spread apart from each other, this causes the ice to float on top of liquid water
If water sank when frozen, bodies of water would eventually freeze We also discuss several other topics like Which plants are considered non-vascular?
completely solid, making like on earth impossible, because there would be little to no liquid bodies of water We also discuss several other topics like What is the difference between speciation and systematics?
Ice on top also insulates the water below it, keeping it from coming into contact with the cold air above and preventing it from freezing, to allow
life to continue below the frozen surface
Water is a Polar Solvent
Hydrophilic substances:
o High affinity for water
Ions and polar molecules
Hydrophobic Substances
o Low affinity for water
Nonpolar molecules / nonionic elements
Ex: oil will not mix with water, you can shake it and get little blobs of oil, but after time it will completely separate again, the oil pieces connect back to each other because it is protecting the inner molecules of oil from
coming in contact with water
Compounds dissolve in water to form a Solution
o Most biological reactions occur in water If you want to learn more check out What do you call the act of buying and selling?
Measuring Chemicals in a Solution
o Solvent – the dissolving agent of a solution
o Solute – the substance that is dissolved
Concentration – how much of the solute is present per volume of solvent in moles (Molar (M))
1M = 1 mole of solute per liter of solvent
pH Affects Living Organisms
A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other
o The hydrogen atom leaves its electron behind and is transferred as a proton, or hydrogen
Pure water – H+ and OH concentrations are EQUAL [H+] = [OH]
pH = log[H=]
pH = A measure of the concentration of H+ ions in solutions [H+]
Pure water: [H+] = 10^7 M > pH= 7
The greater [H+], the more acidic the solution is
pH < 7 – acidic
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pH = 7 neutral We also discuss several other topics like What are the domains of the superego?
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pH > 7 basic
For each change in pH by 1 unit, [H+] changes 10fold
Example:
Cola – pH 3 = [H+} = 10^3M
Pure Water – pH 7 = [H+] = 10^7M
Cola is 10,000 more acidic than pure water
BY changing the concentrations of hydrogen and hydroxide ions in solution Acid: any substance the increases the [H+] of a solution
Base: Any substance that reduces the [H+] of a solution
Controlling pH is important for cells
Biological reactions have an optimal pH (68)
Chapter 3: Organic Molecules
Carbonbased molecules
The dry matter of organisms consists mainly of organic molecules Advantage of Carbon as a building block for life
o Carbon is TETRAVALENT
Needs 4 electrons to fill valence shell
Capable of making 4 chemical bonds
Large, complex, & Diverse molecules
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