chapter 2: atoms, molecules & life - western oregon …guralnl/gural/102chapter 02 -...

Chapter 2:Atoms, Molecules & Life

Chapter 2: Atoms, Molecules & Life

What Are Atoms?

Answer: The smallest unit of matter

Composed of:1) Nucleus (in the middle)

• Protons (positively charged particles)• Neutrons (neutrally charged particles)

2) Electrons (negatively charged particles)• Orbit the nucleus

An atom is electrically neutral (protons = electrons)


An example ofan atom:


Periodic Table of Elements:

Element = Substance that can’t be broken down or converted to another substance

Atomic Number = Number of protons in the nucleus


Atomic Mass = Number of protons & neutrons in nucleus

Isotope = The same element with a differentnumber of neutrons

• C14 • P32 • U235



Electrons:

A) are repelled from one another (- charge)B) are attracted to the nucleus (+ charge)

Electrons orbit the nucleus in 3-dimensional spaceforming electron shells:

• First shell (2 electrons)• Second shell (8 electrons)• Third shell (8 electrons)


Inert Atoms = Atoms with their outermost shell either completely full or empty

Reactive Atoms = Atoms with their outermost shell only partially filled

HydrogenCarbonOxygen

HeliumNeonArgon


How would you make these atoms stable?

(Figure 2.3)


Chemical Bonds:Interaction of atoms to stabilize their outermostelectron shells (attractive force)

Molecule = 2 or more atoms of any type held together byinteractive forces

H HO

Water (H2O)

HH

Hydrogen (H2)

Compound = 2 or more atoms of different types held together by interactive forces

Chemical Reaction = making or breaking chemical bonds • Essential for life (and modern society)


Chemical Bond Types:

1) Ionic Bond:Attractive force between atoms that have lost or gained electrons (Ions - charged molecules)

Transfer ofelectrons


Sodium Chloride (NaCl - Figure 2.3)

Ionic Bonds = Weak Bonds



2) Covalent Bond:Attractive force between atoms that share electrons

Sharing ofelectrons

Most biological molecules utilize covalent bonding:

ProteinsCarbohydratesLipidsNucleic Acids

Covalent Bonds = Strong Bonds


Examples of Covalent Bonds:

H - H

Share one pair of electrons (H2)• Single covalent bond

Share two pairs of electrons (O2)• Double covalent bond

O = O

Share three pairs of electrons (N2)• Triple covalent bond N N


Bonding Patterns (Table 2.3):

Carbon (C)

Oxygen (O)


Non-polar Covalent Bonds:Equal sharing of electrons

Polar Covalent Bonds:Unequal sharing of electrons

Molecule is electrically neutralbut

poles are charged due to differences in nuclear attraction for electrons



3) Hydrogen Bond:Attractive force between water molecules

(Figure 2.5)

Positive end of water molecule (H’s) attract negative end (O)

of other water molecule

Due to polar covalent bonds:

Weak Bond


Water = Good Stuff!

Life most likely arose in waterLiving organisms 60 - 90% water

Why is Water so Important to Life?


Importance of Water:

1) Water is an excellent solvent:• liquid capable of dissolving other substances in itself

Dissolving Ionic Bonds:(Salt)

(Figure 2.6)

Polar nature of water

Solution = Fluid containing dissolved substances


• Molecules electricallyattracted to water

• Ions, polar molecules

Hydrophilic Molecules:Water-loving

Hydrophobic Molecules:Water-fearing

• Molecules electricallyneutral (fats / oils)

Dissolving Polar Covalent Bonds:(e.g. glucose)

+ -

• Molecules tend to clumptogether in water(Figure 2.7)



2) Water molecules tend to stick together (cohesion):• Surface Tension: Tendency for a water surface to

resist breaking

Walk onwater

Flow againstgravity

• Adhesion: Tendency for water to stick to walls of surfaces



3) Water Can Form H+ and OH- Ions (ionization):

H2O H+ OH-+Pure water contains equal amounts of H+ and OH-

HCl Acidic

H+ = OH-

Water

H+ = OH-

Water

NaOHBasic

OH-H+ <H+ > OH-


The pH of a solution describes its degree of acidity:

(Figure 2.8)


Buffers maintain a solution at relatively constant pH:• Stable pH essential for normal function

• Buffers either accept or release a H+ in response to changes in pH

Example: Bicarbonate ion (HCO3-)

Too acidic?

H+Hydrogen ion

+HCO3-

Bicarbonate ion

H2CO3Carbonic Acid

Too basic?

OH-Hydroxide ion

+H2CO3Carbonic Acid

H20HCO3- +

Bicarbonate ion Water



3) Water Moderates Temperature Changes:

• Slow molecules = Cool temperatures• Fast molecules = Warm temperatures

• Temperature = Speed of moleculesBackground:

A) Water Heats Slowly• Energy first initiates breaking of hydrogen bonds…• Specific Heat = energy needed to heat 1 gram of

a substance 1°C • Specific HeatWater = 1 cal• Specific HeatAlcohol = 0.6 cal• Specific HeatGranite = 0.02 cal



3) Water Moderates Temperature Changes:

A) Water heats slowlyB) Water is an effective coolant

• Heat of Vaporization: Heat needed to convert liquidwater to water vapor

• 529 calories/gram (very high!)By evaporating 1 g of water,

539 grams of human body cools 1° C

C) Water freezes slowly• Moderates the effects of low temperatures

D) Water forms ice (less dense than fluid water):• Acts as an insulator for life below

Transfer ofelectrons

Ionic Bonds:

Sharing ofelectronsCovalent

Bonds:


The Importance of Water:

1) Excellent Solvent2) Cohesion / Adhesion3) Forms Ions (H+ / OH-)4) Moderates Temp.

chapter 2: atoms, molecules & life - western oregon …guralnl/gural/102chapter 02 -...

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