1 Chapter 3 Water and the Fitness of the Environment

Bonding properties How does this atom behave?

H O wants to fill this HH

5 (a) (b) Name (molecular formula) Electron- shell diagram Structural formula Space- filling model Hydrogen (H 2 ). Two hydrogen atoms can form a single bond. Oxygen (O 2 ). Two oxygen atoms share two pairs of electrons to form a double bond. HH O O Figure 2.11 A, B

6 Name (molecular formula) Electron- shell diagram Structural formula Space- filling model (c) Methane (CH 4 ). Four hydrogen atoms can satisfy the valence of one carbon atom, forming methane. Water (H 2 O). Two hydrogen atoms and one oxygen atom are joined by covalent bonds to produce a molecule of water. (d) H O H HH H H C Figure 2.11 C, D

H H Oxygen + + – – – – Because oxygen (O) is more electronegative than hydrogen (H), shared electrons are pulled more toward oxygen. This results in a partial negative charge on the oxygen and a partial positive charge on the hydrogens.

8 Fluorine has the highest electronegativity. Why not neon or helium? Neon/Helium have a full valence shell and therefore are already stable all by themselves and will not attract electrons to be stable. In biology, we will focus on elements with high electronegativity like oxygen and nitrogen.

Oh, look hydrocarbons!

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ions Cation vs. Anion The sodium and chloride ions are now attracted to each other and form an ionic bond. ionic bond = bond between two oppositely charged ions

-Na + Cl - crystals are repeating arrays of Na + and Cl - held together by the electromagnetic force. -general name given to ANY ionic compound (not just sodium chloride (Na + Cl - ) held together in a lattice structure. Ex: Na + Cl - K + Cl - Mg 2+ Cl 2 -

Even non-polar molecules can have some positively and negatively charged region briefly and can very weakly bind to another. 1. Two non-polar molecules (say H 2 ) come into close proximity 2. By chance, the position of the electrons around one of the molecules (the one to the left) are more on one side of the molecule than the other causing one side to be slightly negative and the other side to be slightly positive. 3. This will then induce a dipole in the neighboring molecule as the neighboring molecule’s electrons will be attracted to the slightly positive region of the first molecule resulting again in an ever so slightly negative side and an ever so slightly positive side. Of course, the negative and positive will form a very weak interaction.

16 ◦ Reinforce the shapes of large molecules ◦ Help molecules adhere to each other Plasma membrane are stabilized by the additive affect of Van der Waals interactions between non-polar fatty acid tails of phospholipids. H bonds The two strands of a DNA molecule are held together tightly by the additive affect of many, many weak Hydrogen Bonds

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Water-conducting cells Adhesion Cohesion 150 µm Direction of water movement How is water transported against gravity in plants?

Be able to explain why water resists change in temperature. 1 kcal = 1,000 calories; amount of heat needed to raise the temp of 1kg of water Specific heat of iron: 0.1 cal/g/ o C Specific heat of water: 1 cal/g/ o C (1 calorie)

Water, because of it H-bonding (cohesive nature) has a very high specific heat relative to other molecules. It is difficult to get the water molecules to vibrate since they are all sticking to each other. The H-bonds need to be broken. Think about this analogy: is easy to push a single student and get them moving fast, but if you all hold hands, it becomes more difficult as I would need to break those bonds. Helps organisms resist change in temperature!!

Water has a relatively high heat of vaporization because the hydrogen bonds of the water that must be overcome in order for evaporation to occur

Liquid water Hydrogen bonds constantly break and re-form Ice Hydrogen bonds are stable Hydrogen bond

Solvent: the dissolving agent in a solution Solute: the substance being dissolved Solution: a homogeneous mixture Aqueous solution: water is the solvent

“Cage” of water molecules surrounding each dissolved substance Hydration shell

This oxygen is attracted to a slight positive charge on the lysozyme molecule. This oxygen is attracted to a slight negative charge on the lysozyme molecule. (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. ++ ––

Rule of thumb: LIKE DISSOLVES LIKE

35 Rule of thumb: LIKE DISSOLVES LIKE Soap is AMPHIPATHIC

H Hydronium ion (H 3 O + ) H Hydroxide ion (OH – ) H H H H H H + – + H 2 O H + + OH - The oxygen atom is more electronegative than the hydrogens and pulls the shared electrons away from them, which can cause one of the hydrogens (a proton) to fall off.

10 –1 H + Ion Concentration Examples of Solutions Stomach acid, Lemon juice 1 pH 10 0 Hydrochloric acid0 10 – –3 Vinegar, cola, beer 3 10 –4 Tomatoes 4 10 –5 Black coffee, Rainwater 5 10 –6 Urine, Saliva 6 10 –7 Pure water, Blood 7 10 –8 Seawater 8 10 –9 Baking soda 9 10 –10 Great Salt Lake –11 Household ammonia –12 Household bleach –13 Oven cleaner –14 Sodium hydroxide14 tenfold change in H+ ions pH1  pH  times less H + pH8  pH  times more H + pH10  pH  times more H +

pH = - log [H + ] [H + ] = M pH = - log [H + ] x = - log [10 -6 M] pH = 6 pH = - log [10 -7 M] pH = 7 [H + ] = M What if the pH is 10 X higher? 1. As [H + ] goes up, pH goes DOWN 3. A change in 1 pH corresponds to a 10 - fold change in [H + ] 2. As [H + ] goes down, pH goes UP

How many times more acidic is lemon juice than urine? 10,000X more acidic

How many times more basic is milk of magnesia (pH 11) compared to seawater (pH 8)? 1000X more basic

1. What does the pH value tell us about the solution? 2. What happens to the pH as the [H + ] increases? 3. If the pH of a solution is increased by three pH units, how has the [H + ] changed? The H + (free proton) concentration [H + ] decreases 1000x lower [H + ]