When two or more atoms really
love each other… they bond 
Chemical Bonds
 Attractions arising from the sharing or transfer of
valence electrons.
 Bonds can be INTER-molecular or INTRA-molecular
 Intramolecular: within a molecule
 Covalent – sharing
 Ionic – transferring
Covalent Bonds
 Sharing of a pair of valence electrons.
 2+ atoms covalently bonded = MOLECULE
 Pure substances vs. Compounds
 H2

H2O
More on covalence…
 Electronegativity: attraction of a particular atom for
the electrons of a covalent bond.


Nonpolar covalent bonds: when electrons share equally
Polar covalent bonds: when electrons are not shared equally
Ionic Bonds
 Occurs when there’s an imbalance in electrons
 When electrons are transferred, ions are formed
Types of ions
 Ions = charged particles

Cation = positive ion


 Break down these ions:
Na+
Anion = negative ion

Cl-

MgO

K2O

CaCl2
Ionic Compounds = Salts
 Environmental conditions impact strength of ionic
bonds.

Dry conditions: Ionic bonds are stronger

In water: ions dissociate (water = universal solvent)
Weaker Chemical Bonds
 Hydrogen bonds: Attraction of “charged” hydrogen
bonded with another atom to another different atom
nearby.
Weaker Chemical Bonds
 Van der Waals Interactions: Electrons distribute
unevenly creating slightly positive and negative
regions.
Molecular Shape and Function
 Molecular shape dictates their function in ALL of
biology!
 Ex: Proteins, hormone receptors, blockers
Chemical Reactions
 Formation and destruction of
chemical bonds are called
chemical reactions.
 Reactants: starting materials
 Products: materials after
chemical conversion
Photosynthesis & Cellular Respiration
 Photosynthesis:
 6CO2 + 6H2O  C6H12O6 + 6O2
Photosynthesis & Cellular Respiration
 Photosynthesis:
 6CO2 + 6H2O  C6H12O6 + 6O2
 Cellular Respiration:
 C6H12O6 + 6O2  6CO2 + 6H2O + ENERGY!!!!!
Properties of Water
Water Lab – Activity #1
 Penny Challenge. Determine how many drops of water
you can fit onto the HEADS side of a penny vs. the tails
side of a penny. Record data for two trials for each side
in your notebook. Leave space for class data before
recording information for Challenge #2.
 Challenge #2: Spread a thin layer of dish soap on top of
your penny and try the Penny Challenge again. BEFORE
YOU START, write down your hypothesis for what will
happen.

If dish soap is spread onto the heads/tails side of my penny, the
number of drops will... because…
Why is water so important?
 Cells are mostly water (70-95%)
 Cells are mostly surrounded by water.
The Water Molecule
 POLARITY: Oxygen has a
stronger pull of the
electrons than the hydrogen
atoms.



Oxygen – slightly negative at any
given time.
Hydrogen – slightly positive.
Water takes on bent shape.
Water molecules can attract each other
 Because water molecules are charged, they can
attract each other or other ions. (Hydrogen Bonds!)
 COHESION – attraction of water molecules to itself
 ADHESION – attraction of molecules to other
substances.
Examples of Forces
 Surface Tension: A
measure of how difficult
it is to stretch/break
liquid surfaces
 Capillary Action:
Forces that draw water
out of the roots of a
plant and up the step
and leaves.
Capillary Action
Moderation of Temperature
 Water can store/release heat without too
much change in its own temperature.
 Thermal energy is a reflection of both
the mass and movement of water.
Bodies of water have a large mass
therefore have high thermal energy!
 When two temperatures are brought
together, they try to reach equilibrium.
Measures of Heat
 Calorie = amount of heat it takes to raise the
temperature of 1 g of water 1 degree Celsius.
 Kilocalorie = 1,000 cal.
 SPECIFIC HEAT = the amount of heat needed to
change 1 g of that substance by 1 degree.

Water resists changing temperature.
Evaporative Cooling
 Heat of Vaporization:
Quantity of heat a liquid
must absorb for 1 g to be
converted from liquid to
gas.
 High compared to other liquids.
H-bonds?!
 Evaporative Cooling: As
liquid evaporates, it pulls
heat away with the
vaporized liquid.
Remaining liquid is cooler!
Water, when it gets chilly!
Why do ice cubes float in water?
•I C E E X P A N D S W H E N I T
F R E E Z E S ! ( 0 - 4 0C )
•T H I S M A K E S I T L E S S D E N S E
THAN WATER – SO IT FLOATS!
•W H A T I M P A C T D O E S T H I S
HAVE ON THE WORLD?
SOLUTIONS & SUSPENSIONS
 MIXTURES – material composed of two or more
elements or compounds that are physically mixed
but not chemically combined.

SOLUTIONS – Homogenous mixture of two or more
substances. The dissolving agent is the SOLVENT the
dissolved substance is the SOLUTE.

SUSPENSIONS – Heterogeneous mixture
Dissolving Salts
 Positively charged H in water surround chlorine
anions.
 Negatively charged O in water surround sodium
cations.
 Polar water molecules form a HYDRATION
SHELL.
Hydrophilic and Hydrophobic Substances
 Hydrophilic - <3’s water!
 Affinity for water, doesn’t necessarily dissolve!
 Hydrophobic – hates water
Hydrogen has had ENOUGH!
 Hydrogen will leave a water molecule, leaving the
electron behind.



Hydrogen ion: H+ (a lonely proton).
Hydroxide ion: OH- (what H+ left behind!).
Hydronium ion: H+ can’t exist on it’s own, it attaches to the
other water molecule (H3O+)
CONVENTION: H+ represents H3O+
This is RARE
 1.0×10−14 moles of ions per LITER of water.
 BUT, important things happen when the balance
between H+ and OH- ions is broken…
 **Convention** H+ represents H30+
Acids & Bases
 ACIDS have higher [H+]
ions than pure water, pH
value is below 7.
 Examples of Acids



Stomach acid – HCl (~1.5)
Juices (~3.5)
Milk (~6.5)
 Basic, or alkaline,
solutions have lower
concentrations of [H+]
ions. pH value is above
7.
 Examples of Bases:



Blood (~7.4)
Milk of Magnesia (~10.5)
Ammonia (~11.5)
Bases
 Some bases are H+ acceptors.
 Others dissolve to form hydroxide ions [OH-].
 BOTH of these will reduce overall [H+].
The pH Scale
 pH = Potential Hydrogen
 Indicates concentration of H + ions
in solution [H+]
 If [H+] = [OH-] the solution is
neutral (like water!)
 pH = -log[H+]
 Change in pH is TENFOLD!
BUFFERS
 pH of our body must stay around
6.5-7.5; certain systems have a
smaller range of acceptable pH.
 BUFFERS – Weak acids or bases
that can prevent sharp changes in
pH. Accepts or donates H+ ions.
 Example – Carbonic Acid
Bicarbonate in Blood.
Acidification!
 Burning of fossil fuels creates an abundance of carbon
compounds in the atmosphere.
 Reaction with water  ACIDIC!
 25% of the CO2 is absorbed into the ocean and impacts
the marine ecosystems.