Chapter 2
The Chemical Context of Life
Basic Terms

Element = cannot be broken down
to other substances


Examples: Na, O, C, Cl
Compound = combination of 2 or
more different elements

Examples: NaCl, CO2, CH4
Requirements for Life

92 natural
elements…



25 are essential to
life
Carbon, oxygen,
hydrogen, and
nitrogen make up
96% of living
matter
Trace elements are
needed, too,
though

Iodine…lack of =
goiter!!
Atomic Structure


Atom = smallest possible amount of
an electron that retains the
element’s properties
Subatomic particles:



Protons = + charge
Electrons = - charge
Neutrons = neutral charge
Atomic Structure

Atomic Number:


# of protons (also equals # of
electrons…)
Mass Number:

# of protons + # of neutrons

Examples
Isotopes

Def’n: atoms that have more
neutrons than atoms of the same
element


Same number of protons, but different
number of neutrons
Therefore…different atomic mass!
Radioactive Isotopes

Radioactive Isotopes:


Nucleus decomposes spontaneously,
giving off particles and energy (ie.
Carbon 14)
Uses:


Dating fossils
Tracers

marking something and finding it again
later
Energy


Energy = the ability to do work
Energy levels

Further out = more energy
Electron Orbitals

Electrons move within orbitals

Orbitals are 3-D spaces, not linear
Valence Shells




Valence shell =
outermost energy level
Valence shell
determines an atom’s
reactiveness
Alone =
reactive/unhappy!
Paired =
nonreactive/happy !
Chemical Bonding

2 types of bonding that occurs
between atoms:


Covalent bonding
Ionic bonding
Covalent Bonds


Def’n: 2 atoms
share a pair of
valence electrons
Valence = bonding
capacity
Covalent Bonds

Nonpolar covalent bonds


Polar covalent bonds


Electrons are shared equally between 2 atoms
Electrons are NOT shared equally between 2
atoms
Whether a bond is nonpolar and polar is
determined by an atom’s electronegativity

Electronegativity = how much an atom wants
to pull its electrons to itself
Ionic Bonds

Def’n: one atoms “donates” its electrons
to the other


Cation = atom that donates, +
Anion = atom that receives, -
Hydrogen Bonds



A hydrogen atom that
is covalently bonded to
one electronegative
atom is also attracted
to another
electronegative atom
Usually between
oxygen of one water
molecule and
hydrogen of another
Individually weak, but
strong together!
Molecular Shape & Function


Molecules have characteristic sizes
and shapes
Molecular shape is crucial in
biology because it determines how
biological molecules recognize and
respond to each other with
specificity

Examples: ??
Applications

Morphine


Lock and key concept
Morphine is designed
to be the same shape
as endorphins



Therefore,
morphine will bind
to the endorphin
binding site in the
brain
Brain will be
tricked!
Heroin works in the
same way
Chemical Reactions



Def’n: the making and
breaking of chemical
bonds
Reactants  Products
1st Law of
Thermodynamics:

Energy can be neither
created nor destroyed