05chapter2

Chapter 2 The Chemistry of Life: 

Chapter 2 The Chemistry of Life 09-04 ekgh from Biology (Visual Resource Library)– Raven/Johnson Life – Lewis/Gaffon Biology Concepts & Connections – Campbell Unity and Diversity of Life – Starr / Taggert

THE CHEMISTRY OF LIFE: 

10 – 20 BYA the Universe begins. Physics and Chemistry are basic to the study of biology THE CHEMISTRY OF LIFE

Slide3: 

A. Matter Material that takes up space. 1. Elements Pure chemical substances composed of atoms. Examples? How many elements exist? How many of these elements are essential to life?

Slide4: 

Periodic Table of Elements

Slide5: 

2. Atom The smallest “piece” of an element that retains the characteristics of that element. Composed of 3 subatomic particles: Protons Neutrons Electrons

Slide6: 

Characteristics of Subatomic Particles

Slide8: 

Atomic number # protons in nucleus of an atom (establishes identity of the atom) Since most atoms are electrically neutral, atomic number indicates # of electrons as well. Atomic mass # protons plus # neutrons in nucleus of an atom. Mass is measured in Daltons. 6.02 x 1023 daltons = 1g Protons and Neutrons = 1d Electrons = 1/1840 d

Slide9: 

How can we determine the number of neutrons in an atom? # neutrons = atomic mass - atomic # Determine # neutrons in a carbon atom (atomic mass = 12; atomic # = 6). # neutrons = 12 - 6 = 6 Do all carbon atoms have the same number of protons? Do all carbon atoms have the same number of neutrons?

Slide10: 

Isotopes Atoms having the same number of protons, but differing numbers of neutrons. So their mass is different. Neutrons determine nuclear stability. Ex. Carbon isotopes carbon 12 (12C)  6 neutrons 99% of C isotopes carbon 13 (13C)  7 neutrons carbon 14 (14C)  8 neutrons Which is most stable? Unstable isotopes tend to break into more stable forms releasing radioactivity

Slide11: 

Periodic table information on carbon: Atomic mass given in table is average mass of all the element’s isotopes.

Slide13: 

3. Compound A pure substance formed when atoms of different elements bond. Examples: CO2 carbon dioxide H2O water CH4 methane C6H12O6 glucose

Slide15: 

4. Molecule Smallest piece of a compound that retains characteristics of that compound. The number of molecules is written as a coefficient. Examples: 4CO2 4 molecules of carbon dioxide 2C6H12O6 2 molecules of glucose 6O2 6 molecules of oxygen

Slide16: 

5. Chemical Bonds Type of bond formed is determined by the number of valence electrons in the interacting atoms [octet rule]. a) Covalent bonds - form when atoms share electron pairs. strongest type of bond tend to form when atoms have 3, 4 or 5 valence electrons can be nonpolar or polar

Slide19: 

Nonpolar covalent bonds - electrons are shared equally between atoms. Ex. methane

Slide20: 

Polar covalent bonds - electrons are drawn more strongly to one atom’s nucleus than the other. Form when less electronegative atoms bond with more highly electronegative atoms. Electronegativity is the tendency of an atom to attract electrons O2 is highly electronegative. Ex. water

Slide21: 

b) Ionic bonds - form when oppositely charged ions are attracted to each other. weaker than covalent bonds atoms with 1, 2 or 3 valence electrons give up electrons to atoms with 7, 6 or 5 valence electrons form salts also found is certain polypeptides Ex. NaCl

Slide23: 

c) Hydrogen bonds - form when opposite charges on two molecules are attracted to each other. weakest type of bond* but in large numbers they provide strength/stability – like teeth on zipper Ex. DNA Ex. Water drop BETWEEN molecules. WITHIN water molecule = covalent bonds H2O

Slide25: 

Covalent bond

Slide26: 

Water is cohesive and adhesive Water has a high Specific Heat Water has a high Heat of Vaporization Frozen Water has a lower density than liquid water Water is an excellent solvent THE PROPERTIES OF WATER

#1 Property of water: Water is Cohesive and Adhesive: 

Cohesion = attraction between like substances Insects can walk on water due to surface tension created by cohesive water molecules Rocks skip Result: water flows freely, molecules don’t separate from each other. Ex. Blood (it’s 80% water) #1 Property of water: Water is Cohesive and Adhesive Figure 2.11

Adhesion: 

Adhesion Due to hydrogen bonding, water molecules can adhere to molecules of other polar substances. Movement up glass tube because surface electric charge attracts water = “Capillary Action” #1 Property of water: Water is Cohesive and Adhesive

Results of Cohesive - Adhesive Property of Water: 

Results of Cohesive - Adhesive Property of Water Adhesion at work: Water moves up Xylem tubes in plants via capillary action

#2 Property of Water: High Specific Heat (High Heat Capacity): 

Because Water’s hydrogen bonds absorb heat when they break and release heat when they form, they moderate temperature It takes a lot of energy to disrupt hydrogen bonds Result: water is able to absorb a great deal of heat energy without a large increase in temperature As water cools, a slight drop in temperature releases a large amount of heat Large bodies of water loose heat slowly. The Atlantic Ocean is at perfect swimming temperature right now. Living organisms in large bodies of water benefit from this #2 Property of Water: High Specific Heat (High Heat Capacity)

#3 Property of Water: Water has a high heat of vaporization: 

Water has a high boiling point 100 Co It takes high energy to break H bonds  Sweat H bonds absorb heat when they break. A water molecule takes a large amount of energy with it when it evaporates This leads to evaporative cooling Figure 2.12 #3 Property of Water: Water has a high heat of vaporization

#4 Property of water: Ice is less dense than liquid water [Ice Floats]: 

Molecules in ice are farther apart than those in liquid water #4 Property of water: Ice is less dense than liquid water [Ice Floats] Figure 2.13 Hydrogen bond ICE Hydrogen bonds are stable LIQUID WATER Hydrogen bonds constantly break and re-form

Ice is therefore less dense than liquid water, which causes it to float: 

Ice is therefore less dense than liquid water, which causes it to float Frozen water Frozen benzene If ice sank, it would seldom have a chance to thaw Ponds, lakes, and oceans would eventually freeze solid And why would this be bad…… What benefit does floating ice provide…

#5 Property of Water: Excellent Solvent : 

Water is a strong solvent because it separates charged atoms or molecules Solutes whose charges or polarity allow them to stick to water molecules dissolve in it They form aqueous solutions #5 Property of Water: Excellent Solvent Figure 2.14 Ions in solution Salt crystal Cl– Na+ Cl– – – – – – Na+ + + + +

# 5 Water is an excellent solvent: 

The nature of the water molecule, specifically, its polarity, makes it an excellent solvent. if the Atoms in a covalently bonded molecule share electrons equally, creating a nonpolar molecule Fats. Insoluable in polar molecules If electrons are shared unequally, a polar molecule is created # 5 Water is an excellent solvent

Slide36: 

This makes the oxygen end of the molecule slightly negatively charged The hydrogen end of the molecule is slightly positively charged Water is therefore a polar molecule In a water molecule, oxygen exerts a stronger pull on the shared electrons than hydrogen Figure 2.9 (–) O (–) (+) (+) H H This makes the oxygen end of the molecule slightly negatively charged The hydrogen end of the molecule is slightly positively charged Water is therefore a polar molecule

Result: Water’s polarity leads to hydrogen bonding and other unusual properties: 

The charged regions on water molecules are attracted to the oppositely charged regions on nearby molecules This attraction forms weak bonds called hydrogen bonds Result: Water’s polarity leads to hydrogen bonding and other unusual properties Figure 2.10A Hydrogen bond

Slide38: 

Like no other common substance, water exists in nature in all three physical states: Campbell Figure 2.10B as a solid as a liquid as a gas

The chemistry of life is sensitive to acidic and basic conditions: 

A compound that releases H+ ions in solution is an acid. Proton donor. one that accepts H+ ions in solution is a base Acidity is measured on the pH scale: pH = -log[H] 0-7 is acidic 8-14 is basic Pure water and solutions that are neither basic nor acidic are neutral, with a pH of 7 Because – when water dissociates it forms equal amounts of H+ and OH- The chemistry of life is sensitive to acidic and basic conditions

Slide41: 

The pH scale Figure 2.15 pH scale Acidic solution Neutral solution Basic solution Increasingly ACIDIC (Higher concentration of H+) Increasingly BASIC (Lower concentration of H+) NEUTRAL [H+] = [OH–] Lemon juice; gastric juice Grapefruit juice Tomato juice Urine PURE WATER Seawater Milk of magnesia Household ammonia Household bleach Oven cleaner Human blood H+ OH–

The math behind pH: 

The math behind pH substance [H] log[H+] pH Gastric juice .01 10 -2 2 Pure water .0000001 10-7 7 Ammonia .00000000001 10-11 11 The pH scale is logarithmic: a change in 1 on the scale means there’s a 10 fold change in H+

Slide44: 

Acids & Bases Acids - substances that add H+ to a solution. Neutral Bases - substances that remove H+ from solution by combining with them. pH scale is measure of acidity/alkalinity based on H+ concentration. Each unit represents 10 fold change in H+ concentration So… tomato juice = ____x greater [H+] than coffee

Slide45: 

Cells are kept close to pH 7 by buffers Buffers are substances that resist pH change. “reservoirs for H+ They accept H+ ions when they are in excess and donate H+ ions when they are depleted Buffers are not foolproof

Connection: Acid precipitation threatens the environment: 

Some ecosystems are threatened by acid precipitation Acid precipitation is formed when air pollutants from burning fossil fuels combine with water vapor in the air to form sulfuric and nitric acids Connection: Acid precipitation threatens the environment Figure 2.16A

Slide47: 

These acids can kill fish, damage buildings, and injure trees Regulations, new technology, and energy conservation may help us reduce acid precipitation Figure 2.16B

Fluctuations in pH kept to minimum by buffers: 

Fluctuations in pH kept to minimum by buffers Buffers Donate H+ ions to basic solutions and removes them from acid solutions Buffers = pairs of compounds, an acid and a base Blood buffers: H2CO3 = carbonic acid and HCO3- = bicarbonate ion

Slide51: 

The End