THE CHEMISTRY OF LIFE
Chapter 2
Biology – Miller • Levine
ATOMS
Basic
unit of matter
 From
the Greek word atomos,
which means “unable to be cut”
 Subatomic particles:
Protons – positive charge (p+)
Neutrons – neutral, no charge
(n0)
Electrons – negative charge (e-)

ATOMS
 Nucleus
– contains
protons & neutrons
 Electron cloud –
area where electrons
are located around
the nucleus
 Atoms are neutral
because p+ = e-
ELEMENT
A
pure substance that consists
entirely of one type of atom
 Periodic Table of Elements:
Represented by a 1 or 2 letter symbol
 Atomic number - # of protons
 Mass number – protons + neutrons

ELEMENTS
ISOTOPES
 Atoms
of the same element that have
a different number of neutrons
 Radioactive isotopes – isotopes that
are unstable and give off radiation

Can be used in geological dating, to
treat cancer, to kill bacteria in food, &
as “tracers” in medical diagnosis
ISOTOPES
CHEMICAL COMPOUNDS
 Compound
– a substance formed by
two or more different elements
 Chemical formula – shows the
number of each element in a
compound

Ex. H2O
CHEMICAL BONDS
Atoms
in compounds are held
together by chemical bonds
Valence electrons – electrons
that are available to form bonds
3 major types of bonds – ionic,
covalent, and hydrogen
IONIC BONDS
 When
one or more electrons are transferred
from one atom to another
 Oppositely charged ions are attracted to each
other
 Ex. NaCl
COVALENT BONDS
 Form
when electrons
are shared between
atoms
 Molecule – when
atoms are joined
together by a
covalent bond
 Ex. H2O
THE WATER MOLECULE
 Water
is a polar molecule, where the
electrons are not shared equally

There is a – charge near the O and a +
charge near the H
 Hydrogen
bonds – attraction between
the H of one water to the O of another

Weaker than covalent or ionic
HYDROGEN BONDS
COHESION & ADHESION
 Cohesion
– the
attraction between
molecules of the
same substance
 Adhesion – the
attraction between
molecules of
different substances
MIXTURES
 When
two or more elements or
compounds are physically mixed
together but not chemically
combined
 Suspension – a mixture of water
and nondissolved materials

Will settle back out over time
MIXTURES
 Solution
– a mixture in which all
the components are evenly
distributed
Solute – the substance that is dissolved
 Solvent – the substance in which the
solute dissolves


Water is the greatest solvent
SOLUTIONS
ACIDS, BASES, AND PH
A
water molecule can react to form
hydrogen (H+) and hydroxide (OH-) ions
 Acid – any compound that forms H+ ions
in solution (pH less than 7)
 Base – any compound that forms OHions in solution (pH greater than 7)
ACIDS, BASES, AND PH
 pH
scale – a
measurement system
that indicates the
concentration of H+
ions in a solution (014)
 Buffer – weak acids
or bases that react
with strong acids or
bases to prevent
sudden changes in
pH
CHEMICAL REACTIONS
 Process
that changes one set of chemicals
into another set of chemicals
Fe + O2 → Fe2O3
 Reactants – in front of the arrow
 Products – after the arrow

 Law
of Conservation of Matter – matter
can be neither created nor destroyed

Equations must be balanced
ENERGY IN REACTIONS
Endergonic
– reactions that
require an input of energy or
store energy
Exergonic – reactions that
release energy
Activation energy – the
energy needed to start a reaction
ENZYMES
 Some
chemical reactions are too slow or
have too high an activation energy
 Catalyst – a substance that speeds up
the rate of a chemical reaction by
lowering the activation energy
 Enzymes – proteins that are catalysts
EFFECT OF ENZYMES
ENZYME ACTION
 The
enzyme-substrate complex
Substrates – the reactants
 Active site – the place where the
substrates bind to the enzyme
 When the substrates bind to the active
site they form the enzyme-substrate
complex

ENZYME-SUBSTRATE COMPLEX
REGULATION OF ENZYME ACTIVITY
 Can
be affected by pH and
temperature

Most enzymes have an optimal pH and
temperature
 Can
be turned “on” or “off”
 Can be used over and over again