Water, water everywhere! Our old buddy, the hydrogen bond, holds water molecules together. This is called COHESION!
Why is it unlikely that two neighboring water molecules would be arranged like this? H H O O H H What would be the effect on the properties of the water molecule if oxygen and hydrogen had equal electronegativity?
Substances with an affinity for water are hydrophilic—these tend to have partial charges just like water and are polar Substances that do not have an affinity for water are hydrophobic—these are nonpolar compounds usually containing mostly carbon and hydrogen atoms
The importance of water to life Transpiration, the evaporation of water from the leaves of plants, pulls water up from the roots due to the properties of cohesion and adhesion.
Because of hydrogen bonds and cohesion, water has high surface tension. A water strider has legs that are coated with a hydrophobic substance. What might be the benefit? What would happen if the substance were hydrophilic?
Specific heat is the amount of heat needed for 1 g of water to increase its temperature by 1 degree C. The specific heat of water is 1 calorie. That’s higher than most liquids, meaning that water changes temperature more slowly when it absorbs or loses heat. Water keeps air temperatures moderate by absorbing heat from and releasing heat to the air.
The high specific heat of water is due in large part to the H-bonds. The hydrogen bonds need to be broken or made before the molecules can speed up or slow down. How does the specific heat of water affect life?
Ice floats because water expands when it freezes. So oceans and lakes don’t freeze completely solid.
Solution—homogenous mixture of 2 or more substances Solvent—dissolving agent in a solution Solute—what’s dissolved in a solution Aqueous solution—when water is the solvent in a solution Concentration is measured in molarity (M)—number of moles of solute per liter of solution (moles/L)
Acids--increase H+ concentration in a solution Bases—decrease H+ concentration in a solution (increase OH- concentration) pH scale—0-14 0-6.9 is acidic 7 is neutral 7.1-14 is basic
Buffers help to minimize changes in pH by accepting H+ ions when they are too many and donating H+ ions when there are not enough. Ex: the pH of blood is kept at about 7.4 using the carbonic acid buffer system. H2CO3 HCO3- + H+ Response to a rise in pH Response to a drop in pH
Organic chemistry—the study of carbon compounds
Carbon bonds with many different elements because it’s got 4 electrons in its valence shell. Carbon always forms 4 bonds (any combination of single, double, and triple bonds)
Hydrogen can only form single bonds because it can only have 2 electrons. What’s wrong with these structures? H=C=H H-C=C-H
Fats have tails made of hydrocarbons Hydrophilic head Hydrophobic tails Store lots of energy
Isomers—same molecular formula, different structure Structural—atoms connected differently Geometric—different configuration around a double bond Enantiomers—non-superimposable mirror images
Functional groups—parts of organic molecules involved in chemical reactions