Why Study Chemistry in
Biology?
Banana Cell with Starch Granules
The Size of an Atom
The Atom
Definition: smallest particle of an element
C. Composition
Subatomic
Particle
Charge
Mass
Location
Proton
+1
1
Nucleus
Neutron
0
1
Nucleus
Electron
-1
1/1840 the
mass of a
proton
Orbiting
nucleus
D. If Neutral Atom: protons will = electrons
II. Elements
A. Definition: substance that cannot be broken
down into other substances
B. Biologically important elements
i. Major: C H O N
ii. Minor: Ca Fe Mg I Se P K Na Cl
C. Symbol: usually from first letter or two of full
name
Elements Con’t.
Mass Number
Atomic Mass
12.0107 amu
D. Atomic Number: # of protons in
nucleus
i. Mass number: count of the total number of protons and
neutrons in an atom's nucleus
ii. Atomic mass: average mass of an atom based on the
relative abundance of its isotopes
F. Isotopes
i. Definition: forms of the same element have same #
of protons but different # of
neutrons
Mass Number
ii. Radioactive isotopes: An isotope having an unstable
nucleus that decomposes
spontaneously
G. Location of Electrons
i.
First level is closest to
nucleus- holds TWO
electrons
ii. Second level is further
out- holds EIGHT
electrons
iii. Third level can hold up
to 18 electrons
Fill the orbital closest to nucleus first
1. Valence electrons: outermost electrons, participate
in BONDING
See the different
i
levels?!
H. Chemical Compounds
i. Molecules definition: two or more atoms held
together by COVALENT bonds
ii. Compound definition: a substance
containing two or more elements in a
fixed ratio
– Ex: H2O, NaCl
Decoding Chemical Formulas??
C6H12O6
Element
subscript is the
NUMBER of
ATOMS
So in this molecule, there are 6 carbon atoms,
12 hydrogen, and 6 oxygen
2H2O
• The number in front of H2O means
two entire molecules of H2O
• Think of it like 2 x (H20)
• Sooooo… how many total atoms
of H are there?
• Of oxygen?
• Atoms want to fill their outer energy
levels to be
• In order to do this, they will meet up with
other atoms and either share or
exchange electrons
• Atoms share electrons
so that both atoms fill
their outer energy level
B. Ionic Bonds: gimme that electron!
• Atoms transfer electrons, becoming (+) or (-)
charged
• This attraction brings them together
– Ex: Na and Cl
i. Ions
> An electrically charged atom
CATIONS: positively charged ions, have more PROTONS
ANIONS: negatively charged ions, have more ELECTRONS
Hydrogen
Has 1 electron,
needs 1 to fill its
orbital
Carbon
Has 4 electrons in
outer level, needs 4
more to fill its orbital
Can form ONE
bond
Can form FOUR
bonds
V. WATER
LIFE DEPENDS ON THE UNIQUE
PROPERITIES OF WATER
Questions to think about
• Why do put salt on the roads?
• Why do we salt a pot of pasta water?
• At a higher altitude why must we
cook “boil” something longer?
A. Human Composition:
Cells are 70–90% water
B. Plant Composition
As much as 95%
plants can be made
of water
C. Formula:
H2O
D. Bonds:
i. Hydrogen bonds: the slightly (+) H atoms
are attracted to nearby (-) O atoms, and
develop a weak bond.
Hydrogen Bonds
• Hydrogen Bondsweak bonds
slightly positive H
is attracted to the
slightly negative
O of another
water molecule
ii. Covalent bonds: are shared between
oxygen and hydrogen in a single
molecule.
E. Polarity
• Polar molecule:
molecule in which
opposite ends have
opposite electric
charges
• Why? Water is a
polar molecule:
because Oxygen is
an electron HOG
• POLAR COVALENT BOND
The polar nature of water and the
effects of hydrogen bonding explain
most of water's unique properties.
•
•
•
•
•
Cohesion
Adhesion
Solubility
Temperature moderation
The lower density of ice
i. Cohesion
• Definition: Water
“sticks” to each
other
• Surface tension
1-inch
paperclip
over-filled water
3oz Dixie cup
Jesus Christ Lizard
ii. Adhesion
1. Definition: Water
molecules are also
attracted to certain
other molecules.
2. Ex. In
trees/plants water
goes against gravity
Called capillary action
iii. Solubility
Water is the a Universal Solvent
1. Water is able to dissolve other Polar & ionic
compounds when mixed by causing the ions to
break away and surround them.
• Water dissolves Salt (Na+Cl-)
Water (Polar) will not dissolve
(Nonpolar)
• Like dissolve
Like
• Water won’t
dissolve oils
Temperature and Water
Boiling Point: 100 oC
• When you heat
molecules move faster
• When you cool
molecules move
slower
• Water takes more
energy to heat
because energy must
break hydrogen
bonds
212 oF
iv. Boiling Point
Does water boil faster if you add salt to it?
• Water Boils when it has enough energy for the
molecules to leave
v. Freezing Point
0 oC or 32 oF
• What would happen if
our oceans did not
have salt in them?
• Why do we put salt on
our roads?
• Why at effect does salt
have on FREEZING
POINT?
LOW DENSITY OF ICE
• Density- amount of
matter in a volume
• In most substances the
solid state is more dense
than the liquid state
• Water is the opposite
ICE IS LESS DENSE
THAN WATER and will
FLOAT
LOW DENSITY OF ICE
• WHY?????
• Hydrogen
bonds in ice
(solid) keep
molecules
spaced out
LOW DENSITY OF ICE
• Floats
• Ice insulates the
liquid water below
allowing life to persist
G. Acids and Bases
i. A water molecule can react to form ions
ii. An ion is when a molecule breaks down
and the atoms get a charge
1. Example: H+ and OH-
iii. pH Scale
1. How? Scale of 0-14; each pH unit
represents a tenfold change in the
concentration of H+ ions
2. Acid definition: pH 0-6
3. Base definition: pH 8-14
4. Buffer definition: substances that cause a
solution to resist changes in pH.;
works by accepting H+ ions when levels rise
and donating H+ ions when levels fall,
maintaining a constant pH
a. Weak acid or base