CHAPTER 2
CHEMISTRY OF LIFE
2-1 The Nature of Matter

Atom – the basic unit of matter

Atoms are extremely small. 100 million atoms placed side
by side would be about the width of your pinkie.

Atoms contain subatomic particles that are even smaller.
These include protons, neutrons, and electrons.
 Protons
and neutrons have the same mass.
Protons are positively charged particles and
neutrons have no charge (neutral)
 Strong
forces bind protons and neutrons together
to form the nucleus, which is at the center of the
atom.

Electron – a negatively charged particle. It is much
smaller than the proton.

Atoms have an equal number of protons and electrons

Subatomic particles have equal but opposite charges, so
atoms are neutral.

Element – a pure substance that consists entirely of one
type of atom.

More than 100 elements are known, but only about two
dozen are commonly found in living organisms.

Elements are represented by a one or two letter symbol.
 Isotopes
– atoms of the same element that differ in
the number of neutrons they contain
 Ex
– some atoms of carbon have 6 neutrons, some
have 7, and some have 8
 Because
they have the same number of electrons,
all isotopes of an element have the same
chemical properties.
Chemical Compounds

Chemical compound – a substance formed by the
chemical combination of two or more elements in
definite proportions.

Ex.

The physical and chemical properties of a compound are
usually very different from those of the elements from
which it is formed.
Water = H2O
Salt = NaCl
Chemical Bonds
 The
atoms in compounds are held together by
chemical bonds.
 The
main types of chemical bonds are ionic bonds
and covalent bonds.
Ionic Bond – formed when one or more electrons are
transferred from one atom to another
Covalent Bond – forms when electrons are shared between
atoms

Molecule – the smallest unit of most compounds

Van der Waals Forces – a slight attraction that develops
between the oppositely charged regions of nearby
molecules

Van der Waals forces are not as strong as ionic bonds or
covalent bonds but can hold molecules together,
especially when the molecules are large.

Ex – gecko foot

A gecko can climb up walls. Their foot is covered by as
many as half a million tiny hairlike projections. Each
projection is further divided into hundreds of tiny, flatsurfaced fibers. This allows the gecko’s foot to come in
contact with an extremely large area of the wall at the
molecular level. Van der Waals forces form between
molecules on the surface of the gecko’s foot and
molecules on the surface of the wall. The combined
strength of all the van der Waals forces allows the gecko
to balance the pull of gravity.
2-2 Properties of Water
The Water Molecule

A polar molecule is a molecule in which the charges are
unevenly distributed.

A water molecule is polar because there is an uneven
distribution of electrons between the oxygen and
hydrogen atoms.

The negative pole is near the oxygen atom and the
positive pole is between the hydrogen atoms

Cohesion – an attraction between molecules of the same
substance.

Water is extremely cohesive.

Cohesion explains why some insects can walk on a
pond’s surface.

Adhesion – an attraction between molecules of different
substances.

Ex – water in a graduated cylinder adheres to the sides,
causing the sides of water to be higher than the center

Mixture – a material made up of two or more elements or
compounds that are physically mixed together but not
chemically combined.

Ex – salt and pepper mixed together

Solution – mixture of two or more substances in which the
molecules of the substances are evenly distributed

Solute – the substance that is dissolved

Solvent – the substance in which the solute dissolves

Ex – mixing salt into water is a solution. Salt is the solute,
water is the solvent

Suspension – mixture of water and non-dissolved materials
Acids, Bases, and pH

pH Scale – indicates the concentration of H+ ions in solution

The pH scale ranges from 0 – 14. A pH of 7 is neutral. Below 7 is
acidic, above 7 is more basic.

Acid – any compound that forms H+ ions in a solution. Acidic
solutions contain higher concentrations of H+ ions than pure water
and have pH values below 7.

Base – a compound that produces hydroxide ions (OH- ions) in
solution. Basic (alkaline) solutions contain lower concentrations of
H+ ions than pure water and have pH values above 7.

Buffers – weak acids or bases that can react with strong acids or
bases to prevent sharp, sudden changes in pH.
2-3 Carbon Compounds
Four groups of organic compounds found in living
things are carbohydrates, lipids, nucleic acids, and
proteins
 Carbohydrates
– compounds made up of
carbon, hydrogen, and oxygen atoms,
usually in a ratio of 1:2:1
 Living things use carbohydrates as their main
source of energy. Plants and some animals
also use carbohydrates for structural
purposes.
 Lipids
– a large and varied group of biological
molecules that are generally not soluble in water.
They are made mostly from carbon and hydrogen
atoms. Some lipids are fats, oils, and waxes.
 Lipids
can be used to store energy. Some lipids
are important parts of biological membranes and
waterproof coverings.
Nucleic Acids – macromolecules containing
hydrogen, oxygen, nitrogen, carbon, and
phosphorus. They are formed from nucleotides.
 Nucleotides
– consist of three parts: a 5-carbon
sugar, a phosphate group, and an nitrogenous
base
 Nucleic
acids store and transmit genetic
information.
 Two
types of nucleic acids are ribonucleic acid
(RNA) and deoxyribonucleic acid (DNA)

Proteins – macromolecules that contain nitrogen as well
as carbon, hydrogen, and oxygen.

Proteins are polymers of amino acids. Amino acids are
compounds with an amino group (-NH2) on one end and
a carboxyl group (-COOH) on the other end.

Some proteins control the rate of reactions and regulate
cell processes. Some are used to form bones and
muscles. Others transport substances into or out of cells
or help to fight disease.
2-4 Chemical Reactions and Enzymes
 Chemical
Reaction – a process that changes one
set of chemicals into another set of chemicals.
 Reactants
– the elements or compounds that
enter into a chemical reaction
 Products
– the elements or compounds produced
by a chemical reaction
 Chemical
reactions always involve the breaking of
bonds in reactants and the formation of new
bonds in products.
Energy in Reactions
 Chemical
reactions that release energy often
occur spontaneously. Chemical reactions that
absorb energy will not occur without a source of
energy.
 Ex
– hydrogen gas burning with oxygen to
produce water vapor

Activation Energy – the energy that is needed to get a
reaction started

Catalyst – a substance that speeds up the rate of a
chemical reaction. Catalysts work by lowering a
reaction’s activation energy

Enzymes – proteins that act as biological catalysts

Cells use enzymes to speed up chemical reactions that
take place in cells

Enzymes provide a site where reactants can be brought
together to react. Such a site reduces the energy
needed for reaction.
 Substrates
reactions
– the reactants of enzyme-catalyzed
 Enzymes
work best at certain pH values. Many
enzymes are affected by changes in temperature.
 Enzymes
play important roles in regulating
chemical pathways, making materials that cells
need, releasing energy, and transferring
information.