Why are we studying chemistry?

Life requires ~25 chemical elements

About 25 elements are essential for life Four elements make up 96% of living matter:

• carbon (C) • hydrogen (H)

• oxygen (O) • nitrogen (N) Four elements make up most of remaining 4%:

• phosphorus (P) • calcium (Ca)

• sulfur (S) • potassium (K)

Sodium Chlorine Sodiumchloride

Elements and Compounds

Bonding properties

Effect of electrons electrons determine

chemical behavior of atom depends on number

of electrons in atom’s outermost shell valence shell

How does this atom behave?How does this atom behave?

Bonding properties

Effect of electrons chemical behavior of an atom depends on number

of electrons in its valence shell

How does this atom behave?How does this atom behave?

–

–

–

Chemical reactivity

Atoms tend to complete a partially filled valence shell or empty a partially filled valence shell

This tendency drives chemical reactions…This tendency drives chemical reactions…

and creates bondsand creates bonds

–

–

H2 (hydrogen gas)

Covalent bond

Bonds in Biology

Weak bonds hydrogen bonds

attraction between + and – hydrophobic & hydrophilic interactions van derWaals forces (ionic)

Strong bonds covalent bonds

Hydrogen bond

H2O

H2O

Covalent bonds

Why is this a strong bond? two atoms share a pair of electrons both atoms holding onto the electrons very stable

Forms molecules

–

–

H2 (hydrogen gas)H2 (hydrogen gas)

H — H

H2O (water)H2O (water)

H

H

OxygenH

HO

Multiple covalent bonds

2 atoms can share >1 pair of electrons double bonds

2 pairs of electrons triple bonds

3 pairs of electrons

Very strong bonds

H

H–C–H

H

––

More isbetter!

H

H

Oxygen

Polar covalent bonds

Pair of electrons shared unequally by 2 atoms

Water = O + H oxygen has stronger “attractio

n” for the electrons than hydrogen

oxygen has higher electronegativity

water is a polar molecule + vs – poles leads to many interesting

properties of water…

+

+

––

––

Hydrogen bonding

Polar water creates molecular attractions positive H atom in one H2O molecule attracted to

negative O in another H2O also can occur wherever

an -OH exists in a larger molecule

Weak bond

LE 2-7a-1

Transfer ofelectron

NaSodium atom

ClChlorine atom

Ionic bonds are attractions between ions of opposite charge

Na

Sodium ionCl

Chloride ion

Sodium chloride (NaCl)

LE 2-7b

Na

Cl

Sodium chloridecrystal

Ionic attractions are weak, so salts dissolve easily in water.

CHAPTER 3 WATER AND LIFE

More about Water

Why are we studying water?Why are we studying water?

All life occurs in water inside & outside the cell

All life occurs in water inside & outside the cell

Water is a polar molecule- the opposite ends have opposite charges

H2O molecules form H-bonds with each other + attracted to – creates a

sticky molecule

Elixir of Life

Special properties of water cohesion & adhesion

surface tension, capillary action good solvent

many molecules dissolve in H2O hydrophilic vs. hydrophobic

lower density as a solid ice floats!

high specific heat water stores heat

Cohesion & Adhesion

H bonding between H2O molecules is cohesion water is “sticky”

surface tension drinking straw

H bonding between H2O & other substances is adhesion capillary action meniscus water climbs up

paper towel or cloth

How does H2O get to top of trees?

Transpiration built on cohesion & adhesion

Water is the solvent of life

Polarity makes H2O a good solvent polar H2O molecules surround + & – ions solvents dissolve solutes creating solutions

Do you dissolve in water?

Hydrophilic substances have attraction to H2O polar or non-polar?

Or don’t you?

Hydrophobic substances that don’t have an

attraction to H2O polar or non-polar?

fat (triglycerol)

Hydrophilic and Hydrophobic

The special case of ice

Most (all?) substances are more dense when they are solid, butNot water…

Ice floats! H bonds form a crystal

Ice floats

Specific heat

H2O resists changes in temperature high specific heat Water absorbs heat from warmer air and releases

stored heat to cooler air H2O moderates temperatures on Earth

Santa Barbara 73 San Bernardino100

Riverside 96

Pacific Ocean 68

Burbank90

Santa Ana 84 Palm Springs

106

Los Angeles(Airport) 75

San Diego 72 40 miles

70s (F)

80s

90s

100s

Water Ionizes

The covalent bond within a water molecule breaks spontaneously

This produces two ions in a process called ionization because of the great strength of covalent bonds, this does

not occur too often

H2O OH- + H+

Water Hydroxide Hydrogen

pH Scale

pH Scale

Battery acid

Gastric juice, lemon juice

Vinegar, wine,cola

BeerTomato juice

Black coffee

Rainwater

Urine

SalivaPure water

Human blood, tears

Seawater

Inside of small intestine

Milk of magnesia

Household ammonia

Householdbleach

Oven cleaner

Basicsolution

Neutralsolution

Acidicsolution

0

1

2

3

4

5

6

7

8

9

10

Neutral

[H+] = [OH]

Incr

easi

ng

ly B

asic

[H+]

< [

OH

]

Incr

easi

ng

ly A

cid

ic

[H+]

> [

OH

]H+ H+

H+

H+H+

H+

H+

H+

OH

OH

H+

OH

H+

OH

OH

OHOH

H+H+

H+

H+

OHOH

OH

OH OHOH

OHH+

11

12

13

14

1001

2

3

4

5

6

7

8

9

3Amount of base added

Bufferingrange

4 52

pH

Buffers & cellular regulation

pH of cells must be kept ~7 pH affects shape of molecules shape of molecules affect function pH affects cellular function

Buffers minimize changes in concentrations of H+ and OH- in a solution reservoir of H+

donate H+ when [H+] falls

absorb H+ when [H+] rises

CO2

CO2 H2O H2CO3

H2CO3 H HCO3−

H CO32− HCO3

−

CO32− Ca2 CaCO3

Atmospheric CO2 from human activities and its fate

in the ocean

Ocean Acidification

[CO32−] (mol/kg of seawater)

Cal

cifi

cati

on

rat

e(m

mo

l C

aCO

3/m

2 d

ay)

220 280 260 240

20

10

0

GHOSTS

Properties of Water Powerful Solvent

* able to dissolve most chemical compounds, can carry important nutrients in living organisms

High Specific Heat and Heat of Vaporization* can absorb large amounts of heat energy before getting hot, releases heat energy slowly as cools helps to moderate climate, allows organisms to regulate their body temperature

Strong Cohesion* occurs because of hydrogen bonding between water molecules high surface tension

Organizes Nonpolar Molecules* able to form maximum number of hydrogen bonds by excluding nonpolar molecules from disrupting bonding

Water expands as it freezes, becoming less dense than its liquid form

Why is “ice floats” important?

Oceans & lakes don’t freeze solid surface ice insulates water below

allowing life to survive the winter if ice sank…

ponds, lakes & even oceans would freeze solid in summer, only upper few inches would thaw

seasonal turnover of lakes cycling nutrients in autumn