Chemicals of
Life
Chemistry
• chemicals give cells properties of life
–must know principles of chemistry to
understand biology
–organisms-bags of chemicals
–structure determines function
• Hierarchy
• chemicalsorganellescellstissues
organsorganisms
Matter
• living things are made of
matter
–anything that occupies space
& has mass
• composed of elements
Elements
• substances which cannot be decomposed
into simpler substances by chemical
means
• 92 naturally occurring ones
• 25 found in living things
• 96%-H, O, C & N
• 4%-Ca, P, K & S
• trace elements-Fe, Mg, Mn (manganese) & I
– called essential
– cannot live without them
Periodic Table
Atoms
• elements are composed of atoms
• only one kind of atom for each element
– smallest units of matter that retain the
properties of an element
Sub-atomic Particles
• Protons
• Electrons
• Neutrons
–different elements have different
numbers of sub-atomic particles
–chemical & physical differences of
elements are due to these
differences
Sub-Atomic Particles
• Protons
– one positive charge
– found in nucleus of
atom
• Neutrons
– no charge
– found in nucleus of
atom
• Electrons
– one negative charge
– orbit nucleus
Periodic Table
• atom’s structure
determines how
element it comprises
forms compounds &
molecules
• key to this can be
found by knowing
number of sub-atomic
particles an element
possess
• found in Periodic Table
of the Elements
atomic
number-number in upper left corner
atomic weight or mass number-number located on
bottom
Atomic Number
• gives number of
protons in an
atom
• Helium
• Atomic Number
=2
–has 2 protons
Mass Number
• found by adding number
of neutrons & number of
protons
• He = 4
• some atoms of an element
may have different mass
numbers
• these are isotopes
– same number of
protons & electrons but
different number of
neutrons
Number of Electrons
• net charge of an atom is zero
• each proton has one positive
charge
• each electron has one
negative charge
• neutrons have no charge
• to be neural atom must have
the same number of
electrons and protons
• atom of helium with 2 protons
• has 2 electrons
Atomic Number
• How many protons does Sulfur have?
• How many electrons?
• Why?
Chemical Properties
• arrangement of electrons
determines chemical properties of
an atom
• electrons orbit around nucleus
• found at different energy levelsshells
• each shell accommodates a
specific number of electrons
Electron Shells
• innermost shell-2
• 2nd & 3rd-8
• number of electrons in
outermost shell determines
chemical properties of atom
• those with shells that are not
full will interact with other
atoms & participate in
chemical reactions
• those with full shells do not
interact-inert
Electron Shells
• H-only one electron in outer most shell
– very reactive
• C, N, & O
• also highly reactive since outer shells are incomplete
• He-inert or nonreactive because outer shell is full
Reactivity of Chlorine
• Is Chlorine
reactive or not
reactive?
• How can you
tell?
Atom Interactions-Chemical Bonds
• when an atom with an incomplete outer
shell reacts with another atom with an
incomplete outer shell they can interact or
form a bond
• Share
• Donate
• Receive electrons
• in this way both atoms can have a
completed outer shell
Types of Chemical Bonds
• Covalent Bonds
– share electrons
• Ionic
– give or receive
electrons
Sodium & Chloride
Ionic
Bonding
Covalent Bonds
• 2 atoms with incomplete shells
• each share a couple electrons
• so at any one time one atom has a
completed outer shell
• forms molecules
In Class Exercise
• Pretend you are an atom
• Take the number of your birth month as
your atomic number
• Determine the configuration of electrons in
your valence shell
• Find another atom that you might interact
with to form ions or new molecules
• Demonstrate-draw on the board
Chemical Reactions
• elements combine to make molecules &
compounds
• 2 H2 + O2  2H2O
• 2 molecules of H react with one
molecule of O (reactants) to form 2
molecules of water (product)
• arrow indicates direction of reaction
• two sides of equation on either side of
arrow must balance
Water
• single most important
constituent of body
• life on Earth depends on
unusual structure & nature of
water
Importance of Water
• Organisms consist mostly of water
– 2/3rds total body weight of
humans
• Biochemistry is a wet chemistry
– biological molecules do not
react chemically unless in
solution
• Water is an important reactant
– nearly all chemical reactions in
the body occur in water
• Foods are digested to their building
blocks by decomposition reactions
called hydrolysis
– involves addition of water
• When large molecules form from
smaller ones, water is removed in
dehydration synthesis or
condensation reactions
Water Structure
• 2 H atoms attached covalently
to one O2 molecule
• sharing of electrons is not equal
• oxygen pulls more on
electrons than does hydrogen
• electrons spend more time near
oxygen than hydrogen
• unequal sharing producespolar bond
• Nonpolar bond
– bonds in which two atoms
involved have an equal pull
on electrons
Water Structure
• O2 attracts electrons more strongly than Hgiving water an asymmetrical distribution of
charge
• result-V-shape
• H end has positive charge
• Oxygen end has negative charge
• water has 2 poles-polar
• polarity results in weak electrical attractions
between neighboring water molecules
Polarity of Water
• Polarity results in weak
electrical attraction between
neighboring water molecules
• slightly positive Hs in one water
molecule attract slightly
negatively charged O2 in
another water molecule
• opposite electrical charges
attract
• water molecules attract each
othermaking water kind of
sticky
• these weak attractionshydrogen bonds
– much weaker than covalent
or ionic bonds
•
•
•
•
Polarity, H Bonding &
Water’s Properties
cohesive nature
ability to moderate temperature
ice floating
universal solvent properties
Dissociation
• compounds formed by ionic
bonds will ionize or
dissociate in water
• dissociation produces
cations (+) & anions (-)
• aqueous solution containing
anions & cations will conduct
electrical currents
• cations move to negative side
having a + change & anions
move to positive side having
a – charge
• soluble inorganic molecules
whose ions will conduct an
electrical current in solution
are called electrolytes
• NaCl is an electrolyte
• NaCl + H2ONa+ + Cl-
Acids
• H+ & OH- are in solutions at all times
• H2O <-------> H+ + OH- -reversible
reaction
• some compounds add more hydrogen ions
• others remove them
• compound that donates hydrogen ionacid
• HClH+ + Cl• acidic solution is one that has more H+
than OH-
Bases
• compound that accepts or
removes hydrogen ions is a
base
• NaOHNa+ +OH• basic solution- has more OHthan H+
pH scale
• pH = potential hydrogen
• scale developed in
1909 by Dane Soren
Sorensen
– beer brewer looking
for a way to check
acidity of beer
• describes how acidic or
basic a solution is
• scale ranges from 0-14
• 0 = most acidic
• 14 = most basic
• 7=neutral
•
•
•
•
pH
at neutral pH
H+ = OHpH < 7 is acidic
pH > than 7 is more basic or alkaline
Buffers
• pH of blood ranges
between 7.35-7.45
• value must be maintained
in narrow range
• even small change can
lead to severe metabolic
consequences
• biological fluids contain
buffers
– substances that resist
changes in pH by
accepting H+ when in
excess & donating H+
when depleted