The Chemistry of Life:
The Nature of Matter
Biology
Ch. 2
Ms. Haut
Life’s Hierarchical Order
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Atom
Molecule
Organelle
Cell
Tissue
Organ
Organ system
Organism
Population
Community
Ecosystem
Matter is Made of Atoms
• Atom—smallest unit
of matter that cannot
be broken down by
chemical means
• Made up of
subatomic particles
– protons
– neutrons
– electrons
Elements Are the Simplest
Pure Substances
• Elements—substance made of only one
kind of atom
– Elements are represented by a one- or twoletter symbol.
Elements
• The number of protons in an atom of an
element is the element's atomic number.
• Is also the number of electrons
• Atomic weight (mass) is equal to the
number of protons and neutrons
Isotopes
• Atoms of an element that contain a different
number of neutrons
• Identified by their mass numbers
http://www.uwm.edu/Dept/EHSRM/RAD/Figure_1.jpg
Elements and Isotopes
• Radioactive Isotopes
– Their nuclei are unstable and break down at a
constant rate over time, releasing energy
– Although the radiation these isotopes give off
can be dangerous, they have important
scientific and practical uses.
Elements and Isotopes
• Radioactive isotopes can be used:
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•
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to determine the ages of rocks and fossils.
to treat cancer.
to kill bacteria that cause food to spoil.
as labels or “tracers” to follow the movement of
substances within an organism.
BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003
Atoms Can Bond Together
• Chemical compound—substance made
of 2 or more different elements
• Emergent properties—new properties
present at one level that are not seen in
the previous level
sodium + chlorine

sodium
chloride
Atoms Can Bond Together
• Compounds linked together by chemical
bonds
Bond Strength
– Covalent
• Non-polar
• Polar
– Ionic
– Hydrogen
– Van der Waals interactions
Covalent Bonding
• Valence electrons
are shared by
atoms
• Sharing electrons
means that the
moving electrons
actually travel in
the orbitals of
both atoms.
Covalent Bonds
• Electronegativity—the
attraction for electrons
• Nonpolar Covalent
– Electrons are shared
evenly
• Polar Covalent
– One atom more
electronegative than the
other (charged)
– water
Hydrogen Bonding
• Hydrogen atom
covalently bonded to
one electronegative
atom is attracted to
another
electronegative
atom (oxygen or
nitrogen)
• High electronegativity
difference strips
valence electrons away
from another atom
• Electron transfer
creates ions (charged
atoms)
– Cation (positive ion)
– Anion (negative ion)
Na+
Cl–
BIOLOGY: CONCEPTS AND
CONNECTIONS 4th Edition, by Campbell,
Reece, Mitchell, and Taylor, ©2003
http://www.sacbee.com/static/weblogs
/health-andfitness/Salt%2520Shaker.jpg
Ionic Bonding
Van der Waals Forces
van der Waals forces form between
the molecules on the surface of a
gecko’s foot and the molecules on
the surface of the wall, allowing it to
grip the wall
• When molecules are
close together, a slight
attraction can develop
between the oppositely
charged regions of
nearby molecules.
• Not as strong as ionic
bonds or covalent
bonds, they can hold
large molecules
together
The Nature of Matter
The Nature of Matter
The particles that move around the
nucleus of an atom are called
a)
b)
c)
d)
neutrons.
protons.
electrons.
isotopes.
The Nature of Matter
The atomic number of a carbon atom is 6.
How many neutrons does the isotope
carbon-14 have?
a)
b)
c)
d)
6
8
12
14
The Nature of Matter
Which of the following statements about the
three isotopes of carbon is true?
a) They are all radioactive.
b) They have different numbers of electrons.
c) They have the same chemical properties but
differ in atomic mass.
d) They have the same number of protons and
neutrons.
The Nature of Matter
A chemical compound consists of
a) Electrons mixed with neutrons.
b) two or more elements combined in a
definite proportion.
c) two or more elements combined in any
proportion.
d) at least three elements combined by
ionic or covalent bonds.
The Nature of Matter
Van der Waals forces are the result of
a)
b)
c)
d)
unequal sharing of electrons.
ionic bonds.
the bonding of different isotopes.
the chemical combination of sodium and
chlorine.
References
• Unless otherwise noted, illustrations are credited to
Prentice Hall and have been borrowed from Biology
by Miller and Levine, © 2007. These images have
been produced from the originals by permission of
the publisher. These illustrations may not be
reproduced in any format for any purpose without
express written permission from the publisher.