Why Study Chemistry in
Biology?
I. Atoms
Definition: smallest particle of an element
B. 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
C. If Neutral Atom: # protons = # 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
E. Atomic Mass / Mass Number
ii. Atomic mass: count of the total
number of protons and neutrons in an
atom's nucleus
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. 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
A. Covalent Bonds
• 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
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
IV. Water
A.
B.
C.
D.
Human Composition: 65–90% water
Plant Composition: 80-90%
Formula: H2O
Bonds:
i. Hydrogen bonds: the slightly (+) H atoms
are attracted to nearby (-) O atoms, and
develop a weak bond.
ii. Covalent bonds: are shared between oxygen
and hydrogen in a single molecule.
V. Water (con.’t)
5. Water is a polar molecule:
i. Definition of polarity: molecule
that has opposite electrical
charges on opposite ends
ii. Why? Oxygen does not share
electrons equally- pulls them closer
to itself, making it more negative
and Hydrogen more positive
V. Water (con.’t)
F. Unique molecule:
i. Cohesion:
1. Definition: molecules of same
kind stick to one another
2. Example: Surface tension; trees
transporting water from roots to
leaves
ii. Adhesion:
1. Definition: attraction that occurs
between unlike molecules
2. Example: Water molecules and
cotton string.
iii. Solutions:
1. Water is able to dissolve other polar
and ionic compounds when mixed by
causing the ions to break away and surround
them.
Ex.: Salt Water
2. Suspensions
a. Definition: A heterogeneous mixture in
which particles settle out of solvent-like
phase some time after their introduction
b. Example: oil & water
iv. Boiling Point: water will boil at 100C or 212F
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