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CHAPTER 2 – CHEMICAL CONTEXT

OF LIFE

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Matter/ Elements/ CompoundsMatter anything that takes up space and has massElement a substance that cannot be broken down (periodic table)Compound 2 or more different elements (Ex. H20, NaCl); O2 is NOT a compound

4 elements that make up 96% of living things: C, H, N, O

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Trace vs. Essential Elements

Essential Elements necessary for living things (C, H, N, O); make up 96% of all living things

Trace Elements required by an organism but only in minute quantities

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Atoms

Atom – smallest unit of matter that still has all the properties of that element

- made up of a nucleus (protons (+) and neutrons (no charge)) and an electron cloud (electrons (-))

Atomic Number – number of protons in an atom; unique to each element

Mass Number – sum of protons plus neutrons

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IsotopesIsotopes are atoms of the same element that have different numbers of neutrons.

Radioactive isotopes are useful in carbon dating. As they decay, it converts a neutron to a proton…thus changing the identity of that atom. Ex. C14 dating (carbon decays into nitrogen at a fixed rate)

Carbon-14 Dating

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Energy Energy ability to cause change by doing work Potential Energy energy that matter stores

due to structure or location (stored in BONDS!) Kinetic Energy energy of motion

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Energy Levels of ElectronsElectrons FURTHER away from nucleus have MORE energy

Potential Energy – Energy that matter stores due to POSITION or LOCATION

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Electron Shells

Valence # = # of UNPAIRED electrons in outer shell; this is typically the number of bonds the atom can form

When the outer shell is filled, the atom is stable and unreactive. When it is not full, the atom is reactive and can bond with other atoms.

Electrons are arranged in orbitals that give an atom its 3-D shape

Electrons can move energy levels by absorbing or releasing energy

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Covalent Bonding

Covalent Bonding =

SHARING ELECTRONS

Covalent bonds form molecules. Know how many bonds each molecule forms:

Carbon – 4Nitrogen – 3Oxygen – 2

Hydrogen – 1

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Electronegativity

Electronegativity = how strongly an atom “pulls” the electrons in a covalent bond

STRONG electronegative molecules:

Oxygen, Nitrogen, Chlorine

WEAK electronegative molecules: Hydrogen, Carbon

WRITE THIS DOWN!!!

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Polar Molecules - WaterPolar Molecules = Uneven distribution of charge; leads to one side slightly more positive and one side slightly more negative…overall it is uncharged though

Polar Covalent Bonds e- NOT shared equally, found between strong and weak electronegative atoms

NonPolar Covalent Bonds e- shared equally; found between either the same atom (O=O) OR between atoms of similar electronegativities (CH3)

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Ionic Bonds

Ionic Bonds = Giving away/ Taking electrons; Results in ions (charged atoms) which are opposite charges and thus attracted to each other

Cations = positively charged ionsAnions = negatively charged ions

GENERALLY….ionic bonds are between a metal and non-metal.

Called SALTS!

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Hydrogen Bonding

Hydrogen Bonds = Attraction of the hydrogen atom of one molecule (positively charged) to the oxygen/ nitrogen of another molecule (negatively charged)

Hydrogen bonds and polarity are what give water a lot of its properties.

ONE water molecule can form H bonds with up to FOUR other water molecules.

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Van der waals Interactions

Because e- are in constant motion, they can form “hot spots” in molecules; interactions between + and – hot spots are van der waals interactions

These can occur between different parts of the same molecule, or between 2 different ones.

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Chemical Reactions

Chemical Reactions = making and breaking chemical bonds

Reactants = what you start with

Products = what you end up with

Chemical Reactions are affected by the concentration of the reactants….the more reactants, the more collisions, and therefore more product is produced faster!

Chemical Equilibrium = the rate of formation of products is the same as the rate of formation of reactants; no net change on either side of the equation

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CHAPTER 3 - WATER AND THE FITNESS OF THE ENVIRONMENT

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Water – UNIQUE!! ¾ of the Earth’s surface is covered in water Cells are 70-95% water Water is unusual because it exists in 3

states of matter: solid (ice), liquid, gas (water vapor)

Water is a reactant in many chemical reactions

Water is the reason we have life on Earth!

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Water Molecules

-Polarity-Hydrogen Bonds- H2O

Four main properties of water: - Cohesion- Ability to stabilize temperatures- Expansion upon freezing- Versatility as a solvent

Remember, water is a POLAR molecule, so the oxygen side has a slight NEGATIVE charge and the hydrogen sides have a slight POSITIVE charge.

Each water molecule can H-bond with up to 4 neighbors

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CohesionCohesion water sticking to water; it is due to hydrogen bonds; this helps to allow water to move up through the roots in plants

Adhesion water sticking to another substance; ex. Water sticking to the inside of xylem in plants in order to be transported up

Surface Tension the force needed to break the surface of a liquid; this allows some organisms to “walk on water”; water has a very HIGH surface tension

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Ability to Stabilize TemperatureKinetic Energy = Energy of motion (all molecules are in constant motion, so they have kinetic energy)

Heat = TOTAL quantity of kinetic energy of a body of matter

Temperature = AVERAGE kinetic energy in a body of matter

Specific Heat = Amount of heat needed to change 1 gram of a substance by 1 ºC

Measuring Temperature

Calorie = amount of heat it takes to raise 1g of water 1º CKilocalorie (kcal) = amount of heat it takes to raise 1000g (1 kg) of water 1º CJoule = 1 J = 0.239 cal

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Vaporization or Evaporation liquid to gas must move fast enough to overcome attraction to other molecules

Adding heat increases the rate

Heat of Vaporization amount of heat a liquid absorbs for 1g of it to be converted to a gas; Water has a HIGH heat of vaporization

Evaporative Cooling (surface cools/ sweating)

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Water expands upon freezing

Water – the hydrogen bonds are constantly breaking and reforming so the molecules can be packed more tightly together….therefore more dense than ice

Ice – the hydrogen bonds are stable, so the molecules are more spread out….therefore less dense – so they FLOAT on liquid water; due to the structured crystalline lattice; ice can also act as an insulator (think of lakes in the winter)

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Water is versatile as a solvent

Solution = Homogeneous mixture of 2 ore more substancesSolvent = Dissolving agent (usually water)Solute = substance getting dissolvedAqueous Solution = solution where water is the solvent

Water is sometimes considered the “Universal Solvent” ….however , this is inaccurate because it does not dissolve everything. However, it is a great solvent due to the polarity of the water molecules.

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Hydrophobic vs. Hydrophilic

Hydrophilic = water-loving; ionic and polar bonds are hydrophilic; will dissolve in water

Hydrophobic = water-fearing; non-ionic and non-polar substances; does not mix with water (ex. oil)

Waxy cuticle of a plant is hydrophobic

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Moles

Mole (mol) = grams of a substance equal to the molecular weight

Molecular weight = sum of all the weights of all the atoms in a molecule

The advantage of measuring in moles is that one mole of any substance has exactly the same number of molecules as 1 mole of any other substance

- The # of molecules in a mole = Avogadro’s Number = 6.02 x 1023

SO….one mole of any substance will have the same # of molecules, but will weigh different amounts!

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Example from NotesHow to make a 1M solution of Sucrose

- First find the molecular weight of the molecule

- Then you would dissolve 342g of sucrose in water until the whole solution reached 1 liter. That would give you a 1M solution.

- IF you wanted to make a 2M solution, you would multiply the molecular weight by 2 (684g), dissolve it in water, and bring the solution to 1 liter.

- IF you wanted to make a .5M solution, you would multiply the molecular weight by .5 and then add that much solvent (it would be 171g), etc

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PRACTICE!

Make a 1M solution of C6H12O6

C = 12 daltons x 6 = 72 H = 1 dalton x 12 = 12 O = 16 daltons x 6 = 96

180 g = molecular weightSo, dissolve 180g of C6H12O6 in water and fill it up to 1 liter.

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PRACTICE!

Make a .5M solution of C12H22O11

C = 12 daltons x 12 = 144

H = 1 dalton x 22 = 22O = 16 daltons x 11 = 176

342 g = molecular weightSo, multiply 342g by .5 (171g) and then dissolve 171g of C12H22O11 in water and fill it up to 1 liter.

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PRACTICE!

Make a 1.5 M solution of C4H6NO2

C = 12 daltons x 4 = 48 H = 1 dalton x 6 = 6 N = 14 daltons x 1 = 14 O = 16 daltons x 2 = 32

100 g = molecular weightSo, multiply 100g by 1.5 (150g) and then dissolve 150g of C4H6NO2 in water and fill it up to 1 liter.

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Dissociation of Water

-This is a reversible reaction, but does not occur frequently in nature.-H+, OH-, and H3O+ are reactive and can affect cells

This occurs when the hydrogen atom that is attached to one water molecule leaves and goes with another water molecule. The electron does NOT come with it….so the molecule it left is now negative (lost the positive of the H) and the molecule it joined is now positive!

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pH Scales

pH scale – measures the H+ concentration in a solution; 1-14; a change in one number represents a 10 fold difference…6 is 10 times more acidic than 7; 6 is 100 times more acidic than 8

Acids – donate H+ to solutions (increase H+ concentration); the more acidic a substance is, the lower the pH (1-6)

Bases – accept H+ to solutions (decreases H+ concentration); bases have a higher pH (8-14); have higher OH- concentrations

What is the pH??[H+] = 10 - 8

[OH-] = 10 - 3

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BuffersBuffers are solutions that can act as acids or bases (donate or accept H+) to minimize changes in pH. They are very important in living systems. One common buffer in human blood is carbonic acid. It acts as an acid and base pair either accepting OR donating H+ depending on the need of the blood.

Response to a RISE in pH →

H2CO3 ↔ HCO3- + H+←Response to a DROP in pH

H+ donor H+ acceptor Hydrogen (acid) (base) ion Carbonic Acid Bicarbonate ion

Can act as an acid and DONATE H+Can act as a base and ACCEPT H+