The Chemical Basis of Life

Chapter 2

The Atom

The Periodic Table

METALS

NONMETALS

Periodic Table

Ionic Bonding

• Force of attraction between oppositely charged ions• Octet rule….compete outer shell • Cation? Anion? Metal to ?

Covalent Bonding

• Shared electrons• Polar vs nonpolar

Chemical make-up of water

• Water has the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds.

Hydrogen Bonding

Weak bonds between molecules. polar covalent: O- --- H+

Contributes to the special properties of water.

Hydrogen Bonding• Intermolecular vs Intramolecular

Chemistry: Lesson Plan Day 2

• Hand Back & Review Essays/record results• HW due dates- review• Highlight BOTH the properties of water

handout (for water lab) and the buffers handout (prep for our lab)

• Review Properties of water and relate to the water lab

• Second Hour- Acids, Bases, Buffers

Tartigrade……Water Bear

Tartigrade ‘tun’

Properties of Water

*The Importance of Water to Organisms

• High Water Content in living things• Abiotic Factor• Biodiversity• Solvent Properties

Next few slides…for discussion of these topics

Humans

• Up to 60% of the human body is water,(The brain is composed of 70% water, and the lungs are nearly 90% water. Lean muscle tissue contains about 75% water by weight, as is the brain; body fat contains 10% water and bone has 22% water. About 83% of our blood is water, which helps digest our food, transport waste, and control body temperature.)

• Each day humans must replace 2.4 liters of water, some through drinking and the rest taken by the body from the foods eaten.

Water as an Abiotic Factor: it’s everywhere!

• Water is the key to our survival on Earth, it is our source of life

• Water is everywhere! It makes up about 70% percent of the Earth’s surface

• Of that water, about 97% is ocean, and only 3% is fresh water

Water and Biodiversity

The “Universal Solvent”

Water is capable of dissolving a variety of different substances, which is why it is such a good solvent. In fact, water is called the "universal solvent" because it dissolves more substances than any other liquid. This is important to every living thing on earth. It means that wherever water goes, either through the air, the ground, or through our bodies, it takes along valuable chemicals, minerals, and nutrients.

*Properties of Water

• Cohesion• Adhesion• Surface Tension• Capillarity Discuss each/relate to Water Lab

Definitions• Cohesion: Molecules have a strong tendency to ‘stick’ to one

another. -Attraction between like substances-Water is attracted to Water: spherical shape of the mid air

droplet/dome shape on the penny/in the petri dish

• Adhesion: Molecules have the ability to stick (adhere) to one another.

-Attraction between like substances -Water ‘sticks’ to other substances: teardrop shape at the tip

of the pipette/penny/sides of the petri dish/sides of the capillary tubes

Adhesion and Cohesion

• Adhesion Cohesion

….and gravity…

Surface Tension• The property of the surface of a

liquid (water) that allows it to resist an external force, (adhesion) due to the cohesive nature of the (water) molecules.

*Stronger cohesive forces between surface water molecules (and pull downward from those below) than adhesive forces of attraction to the air, creating a supportive ‘skin’.

*Needle is MORE DENSE than the water- should NOT float

Capillary Action

• The movement of water (in a tube) due to the forces of adhesion, cohesion,

and surface tension.

*When the adhesion to the walls is stronger than the cohesive forces between the liquid molecules; limited by surface tension and gravity.

Importance in Biology?

Plants take advantage of capillary action to pull water from the into themselves. From the roots water is drawn through the plant by another force, transpiration.

Which is greater……A or C?

?

Surface Tensionand

Capillary Action

Hydrogen Bonding explains the way water responds to changes in temperature

Hydrogen bonds are formed or broken as water changes from one state to another

To increase the temperature, molecules must be moving faster- much of the energy added to a system is used to break the H-bonds, only a portion is available to speed up movement of the water molecules…(Temp = av. KE)

*High Specific Heat (Heat Capacity)

• Amount of energy required to raise the temperature of water

1 cal/gH2O/1◦C

Importance in Biology?

BECAUSE WATER REQUIRES SO MUCH HEAT INPUT/LOSS TO CHANGE ITS’ TEMP:• Oceans and large bodies of water have relatively constant temperatures• High water content of organisms help them maintain relatively constant internal

temperatures. Biological reactions occur in a relatively narrow temp. range.

*High Heat of Vaporization• Amount of Heat Energy needed to change 1g ofa substance from a liquid to a gas = phase change

• Water: A calorie is the amount of heat energy required to raise the temp. of 1g of water 1◦C

• Water’s Heat of Vaporization- very high compared to other substances due to H-bonds

• Importance in Biology??Exothermic Reaction: Sweating: Evaporative cooling- dissipate xs heat as sweat. Nature- leaves stay cool as transpiration occurs

*Polar Molecule (Solvent Properties)

• Water: The ‘Universal Solvent’ that allows molecules (usually ionic or polar molecules) to dissociate (separate) into individual ions.– Example: NaCl salt :dissolved substance is the

‘solute’

Cushioning: water protects vital organs from jarring

*Wherever water goes, either through the air, the ground, or through our bodies, it takes along valuable chemicals, minerals, & nutrients.

Dissociation of a Water Molecule:Breaking apart into two ions of opposite charge

H2O H+ and OH-

hydrogen ion hydroxide ion

Acids and Bases ?

Acids- Bases

• ACID:Any substance that increases the concentration of hydrogen ions when added to a water solution. (< 7 on the pH scale)– # H+ ions is greater than the number of OH- ions, the

solution is an acid• BASE: Any substance that increases the

concentration of hydroxide ions when added to a water solution– # OH- ions is greater than the number of H+ ions, the

solution is a base

Definition of acids and bases

pH = Powers of Hydrogen Scale 0-14Concentration of free floating H+ determines

the pH (acidity) of the solution

0-14 Acid Base Scale- A Logarithmic Scale ONE pH unit is a tenfold change in

acidity or alkalinity.

A solution with a pH of 4 has 10 times more H+

ions than a solution with a

pH of 5, and 100 times more H+

ions than a solution with a

pH of 6

Strong acids (HCl) and bases (NaOH)

completely dissociate; irreversible

Weak acids and bases do not H2CO3

Carbonic acid

*A reversible reaction

Dissociation of Acids and Bases

Dissociation of a Water Molecule:Breaking apart into two ions of opposite charge

H2O H+ and OH-

hydrogen ion hydroxide ion

H+ = 1 X 10-3 pH = ? Acids and Bases

REVIEW FOR

LAB

Strong acids (HCl) and bases (NaOH)

completely dissociate; irreversible

Weak acids and bases do notH2CO3

*A reversible reaction

Dissociation of Acids and Bases

• pH and Buffers 5.56

• Ocean Acidification 6.38

Buffers• Any substance

that resists changes in pH when an acid or base is added

• Maintain dynamic equilibrium

Carbonic Acid Buffer System in Blood

1. Excessive Protein dieting/Prolonged exercise-muscle overuse2. Impaired lung function/narcotics use (abuse)3. Excess diuretics (Decr. blood volume)/vomiting (loss of stomach acids)4. Hyperventilating

Respiratory Acidosis/Alkalosis Metabolic Acidosis/Alkalosis

Right or Left Shift to fix?Alkalosis vs Acidosis

• Excessive Protein dieting/Prolonged exercise-muscle breakdown or overuse

• XS diuretic use (Decr. blood volume)/vomiting (loss of stomach acids)

• Impaired lung function(emphysema, pneumonia)/narcotics• Hyperventilating

THE PROBLEM:

Effect of [CO2] on Shell Growth Rate

OxidationI sLoss of electrons (H)ReductionIsGain of electrons (H)

Oxidation-Reduction

(Redox) Reactions“OIL RIG”

• Chemical energy = energy stored in bonds.

• Some bonds require more energy to form than others.

• When these high energy bonds break, new lower energy molecules are formed.

• In a redox reaction,the energy differenceis released.

*Supplies energy

*For this reaction

EXERGONIC vs ENDERGONIC

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