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The Chemical Context of Life
CHAPTER 2
Essential Elements of Life
CHNOPS
 Carbon C, Oxygen O,
Hydrogen H, and
Nitrogen N, make up
96% of living matter
 P, S, Ca and K account
for most of the other 4%
 Trace elements, needed
in small quantities by
some species (spp.)

Iodine, human thyroid
gland
Element vs. Compound
 Element:
Can’t be broken down and
still retain the properties
of the element.
 Atoms:
 Nucleus, protons and
neutrons
 Electron Cloud: huge
volume almost no mass
 Mass #: Protons +
Neutrons
 Atomic #: # of protons

 Compound:
Two or more elements
in a fixed proportion
 The properties of the
compound is different
from the elements that
comprise it.

Isotopes and Radioactive Isotopes
 Isotopes:

Elements with a
different number of
neutrons, same # of
protons
 Radioactive Isotopes:
Dangerous to living tissues

However, VERY useful in Biology
Fossil dating
 Tagging DNA for fingerprinting
 Diagnosing illness
 Monitor chemical processes in the
body

Covalent Bonds
 Two atoms share a pair of valence
electrons = molecule
 When two pairs of electrons are
shared = double bond
 Three pairs of electrons = triple
bond
 Remember electrons are shared
only if the molecule has more
stable properties than the single
atoms. This stability happens
because the valence shells of both
atoms are now full.
http://www.armstrongwynne.org/images/bonds.jpg
Non Polar Covalent vs. Polar Covalent
 Non Polar Covalent:

Electrons are shared
equally because of similar
electronegativities
 Polar Covalent

Electrons are shared
unequally because of
electronegativity
differences between .4 and
1.7
http://upload.wikimedia.org/wikipedia/commons/thumb/1/
19/Covalent_bond_hydrogen.svg/700pxCovalent_bond_hydrogen.svg.png
http://academic.brooklyn.cuny.edu/biology/bio4fv/page/image15.gif
Ionic Bonds
 Formed when a
nonmetal strips a metal
of it’s electrons.
 The two atoms have
electronegativity
differences greater than
1.7 (varies w/ text)
 Element with the positive
charge = Cation
 Element with the
negative charge = Anion
http://www.biologycorner.com/resources/ionic_bond.jpg
Amazing Ionic Bonding Joke!
Weak but important chemical bonds
 Hydrogen – formed when a
hydrogen atom covalently
bonded to an electronegative
atom is also attracted to
another electronegative atom

 Van der Waals Interactions

Weak bond
H–O
H–N


occurs between all molecules
because electrons are not
stationary and therefore at
times have a slight charge dipole
Weakest bond
http://productinspiration.com/wp-content/uploads/2008/02/gecko4-h.jpg
Molecule shape and Biological Function
 Molecules that are similarly
shaped, mimic each other in
biological systems.


Morphine, heroin and other
opiates mimic endorphins by
binding to receptors in the
brain. This binding to the brain
receptors triggers euphoria and
relieves pain.
This is why heroin addicts tend
to severely injure themselves
while they are using the drug.
They simply do not feel the
pain.
Chemical Reactions make and break chemical bonds
Photosynthesis is an important chemical
bonds are broken and
reaction:
reformed, leading to new
Sunlight powers the conversion of carbon
arrangements of atoms.
dioxide and water to glucose and oxygen
The starting molecules in
6 CO2 + 6 H20 → C6H12O6 + 6 O2
the process are called reactants,
and the final molecules are
called products.
The reactions must be
“balanced.”
Remember there must be the
same number of atoms of each
type in the products and the
reactants.
 In chemical reactions, chemical

Matter is conserved in a chemical
reaction.

Chemical reactions rearrange matter;
they do not create or destroy matter.
http://thusagricola.typepad.com/photos/uncategorized/2008/10/23/c810x21overview.jpg
You should now be able to:
•
•
•
Identify the four major
elements
Distinguish between the
following pairs of terms:
neutron and proton, atomic
number and mass number,
atomic weight and mass
number
Distinguish between and
discuss the biological
importance of the following:
nonpolar covalent bonds,
polar covalent bonds, ionic
bonds, hydrogen bonds, and
van der Waals interactions
The Chemistry of Life: chocolate
http://www.3dchem.com/imagesofmolecules/Theobromine.jpg