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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