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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)

Chapter 2: Atoms, Molecules & Life

Figure 2.1 – Audesirk2 & Byers

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Periodic Table of Elements:

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

substance (via normal chemical means…)


Atomic Number = Number of protons

in the nucleus

Atomic Mass = Number of protons &

neutrons in nucleus

Chapter 2: Atoms, Molecules & Life (Link)

http://www.youtube.com/watch?v=YvSkXd_VVYk&feature=fvw

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Isotope = The same element with

a different number of

neutrons

• C14 • P32 • U235

Chapter 2: Atoms, Molecules & Life Radioactivity:

Atoms spontaneously

break apart over time…

Radiocarbon Dating:

• Technique for determining the age of materials

that contain carbon based on C14 levels

C14O2


Radioactivity in Research:

C12O2

1 C14 for every

1,000,000,000,000 C12

Half-life

Positron Emission Tomography:

PET

scan

Figure E2.1 – Audesirk2 & Byers

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Periodic Table of Elements:

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

substance (via normal chemical means…)


Key Elements in Living Organisms:

1) Oxygen 2) Carbon 3) Hydrogen 4) Nitrogen

Table 2.1 – Audesirk2 & Byers

• Electrons are: A) repelled from one another (- charge)

B) are attracted to the nucleus (+ charge)

Electrons orbit the nucleus in 3-dimensional space forming electron shells:

• First shell (2 electrons)

• Second shell (8 electrons)

• Third shell (8 electrons)

Electrons Dictate Interactions Among Atoms:


Octet

Rule


• nth shell (8 electrons)

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Life Depends on the Ability of Electrons to Capture / Release Energy:




You are throwing a birthday party and have the option of filling balloons

with a) hydrogen gas or b) helium gas. Both are less dense than regular

air, and both cost the same. Based on their atomic structure, which do

you choose and why?

Question:

Answer: NOT Hydrogen

(link)

http://www.youtube.com/watch?v=w9RZbtA9HVA

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Reactive Atoms:

Atoms with their outermost

shell only partially filled

Carbon

Oxygen

Nitrogen



Inert Atoms:

Atoms with their outermost

shell either completely full or empty

Neon

Argon

Radon

How would you make these atoms stable?



Sodium (neutral) Chloride (neutral)

Full outer

shells

(+) (-)

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Chemical Bonds: Interaction of atoms to stabilize their outermost electron

shells (attractive force)

• Molecule = 2 or more atoms of any type held together by interactive

forces

• 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…)

HH

Hydrogen (H2)

H HO

Water (H2O)



1) Ionic Bond: Attractive force between atoms that have lost or gained

electrons (ions = charged molecules)



Types of Chemical Bonds:

Transfer of

electrons

transferred

electron


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Ionic Bonds = Weak Bonds


1) Ionic Bond: Attractive force between atoms that have lost or gained

electrons (ions = charged molecules)



Figures 2.4 & 2.5 – Audesirk2 & Byers

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




Most biological molecules utilize

covalent bonding:

Proteins

Carbohydrates

Lipids

Nucleic Acids

Covalent Bonds = Strong Bonds

Sharing of

electrons

Hydrogen (H2)


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H - H

Single Covalent Bond:

Share one pair of electrons (e.g., H2)

Double Covalent Bond:

Share two pairs of electrons (e.g., O2)

O = O

Triple Covalent Bond:

Share three pairs of electrons (e.g., N2)N N


Examples of Covalent Bonds:


Common Covalent Bonding Patterns in Biological Molecules:

Table 2.3 – Audesirk2 & Byers

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Molecule is electrically neutral

BUT

Poles are charged due to differences

in nuclear attraction for electrons


Examples of Covalent Bonds:

Non-polar Covalent Bond:

Equal sharing of electrons (e.g., H2)

Polar Covalent Bond:

Unequal sharing of electrons (e.g., H2O)


3) Hydrogen Bond: Attractive force between polar molecules (e.g., water)




Positive end of water molecule

(H’s) attract negative end (O)

of other water molecule

Due to polar covalent bonds:

Hydrogen Bonds = Weak Bonds

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Water = Good Stuff!

Why is Water so Important to Life?

Life most likely arose in water


Living organisms 60 - 90% water

1) Water is an excellent solvent:


Importance of Water:

Solution:

Fluid containing

dissolved substances

Example:

Dissolving ionic bonds (salt)


• Liquid capable of dissolving other substances in itself

Polar nature of water

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Hydrophilic Molecules:

Molecules electrically

attracted to water(ions / polar molecules)

Water-loving

Molecules tend to

clump together in

water


1) Water is an excellent solvent:

• Liquid capable of dissolving other substances in itself


Example:

Dissolving polar bonds (sugar)

Hydrophobic Molecules:

Molecules electrically

neutral(fats / oils)

Water-fearing


2) Water molecules tend to stick together (cohesion):


Link

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

Flow against

gravity

• Surface Tension: Tendency of a water surface to resist breaking

http://www.youtube.com/watch?v=AQ6OtKywyD8

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Pure water contains equal amounts of H+ and OH-

HCl Acidic

H+ = OH-

Water

H+ = OH-

Water

NaOHBasic

OH-H+ <H+ > OH-

H2O H+ OH-+


3) Water can form H+ and OH- ions (ionization):



The pH of a solution describes its degree of acidity:



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Buffers maintain a solution at relatively constant pH:

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

• Stable pH essential for normal function (Human body = 7.3 – 7.4)

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


• Slow molecules = Cool temperatures

• Fast molecules = Warm temperatures

• Temperature = Speed of molecules

Background:

A) Water heats slowly

• Energy first initiates breaking of hydrogen bonds…

• Specific Heat = Energy needed to heat 1 g of a substance 1°C

• Specific HeatWater = 1 cal

• Specific HeatAlcohol = 0.6 cal

• Specific HeatGranite = 0.02 cal


4) Water moderates temperature changes:


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B) Water is an effective coolant


3) Water moderates temperature changes:


• Heat of Vaporization: Heat needed to convert liquid water 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 liquid (unusual…)

http://globalflyfisher.com/gallery/rod-sutterby/pic.php?id=2841&return_to=/gallery/rod-sutterby/index.php&cl=darkframe

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