Chapter 2
Biology
Sixth Edition
Raven/Johnson
(c) The McGraw-Hill Companies, Inc.
Matter is anything
that takes up space
and has weight.
All matter, living or
nonliving, is made
up of elements
Elements contain
atoms, the smallest
unit of matter that
can enter chemical
reactions.
Atoms have a
central nucleus
made up of
protons (+) and
neutrons (o),
and shells
around the
nucleus in which
electrons (-)
orbit.
Fig 2.2
The atomic number = number of protons (#
of protons determines the element).
• protons bear a positive electrical charge
The atomic weight = number of protons plus
number of neutrons.
• neutrons bear no electrical charge
• electrons bear a negative electrical charge
An electrically neutral atom means:
number of protons = number of electrons
Atoms have an atomic symbol, atomic number, and
atomic mass.
Some atoms differ in their number of neutrons and
are called isotopes.
Carbon has 3 isotopes:
• Carbon 12 (most abundant)
• Carbon 13
• Carbon 14 (radioactive - unstable)
Fig 2.3
Which has more mass?
Review of an Atom
3
10
2 in inner shell
8 e- in outer shell
10 e- TOTAL
10 neutrons
10 protons
20 atomic mass units
4
1
e-
9
5
Element = Ne (Neon)
8
2
6
# of protons determine element
7
Atomic number
10
Ne
Atomic mass
20
Chemical Behavior of Atoms
Because an atom’s electrons are relatively far
from the nucleus, the nuclei of two atoms never
come close enough in nature to interact with
each other. Therefore, an atoms electrons
determine its chemical behavior.
Electron Orbital vs. Energy Level
• Electron Orbital – The area around a
nucleus that an electron is most likely to
be found.
• Electron Energy Level – The potential
energy of an electron is directly related to
the distance between an electron and the
nucleus.
– Energy – the ability to do work
Fig 2.4
Only 2 electrons per orbital
Fig 2.5
K only has ‘s’ orbital (1s)
L and M has ‘s’ and ‘p’ orbitals (L: 2s and 2p; M: 3s
and 3p)
Fig 2.7
Elements are arranged in a periodic table
by atomic number and # electrons in outer shell:
1 Electron in Outer Shell
Outer Shell Full
Distribution of the Elements Fig 2.8
Important Atom Characteristics
• Electrons in the outermost energy level
are called valence electrons.
– These are the electrons that determine
the atoms chemistry
• Octet rule (rule of eight) – For most atoms
important to life, the outer energy level
can contain no more than eight electrons.
Fig 2.6
Oxidation – The loss of an electron (atom becomes
electrically positive)
Reduction – The gain of an electron (atom becomes
electrically negative)
Chemical Bonds Build Molecules
• Bonds between atoms can either be ionic,
covalent, or hydrogen.
• Ionic and covalent bonds are the result of
interactions among electrons.
• Hydrogen bonds are attractions between
weakly positive and weakly negatively
charged particles.
Fig 2.9
In ionic bonding, atoms either give up or accept electrons,
resulting in ions (electrically charged atoms/non-neutral).
Ions with opposite charges (- or +) are attracted to each
other and form an ionic bond. (Opposite charges attract, + is
attracted to -, - is attracted to +).
Fig 2.10
In covalent
reactions, atoms
share electrons,
resulting in
covalent bonds.
Covalent Bonds
-build stable molecules
7 e- in
outer
shells
2 shared e- to complete
both outer shells
Aside from single covalent bonds, double,
or triple covalent bonds can form.
Which is stronger?
Why is a molecule formed by
covalent bonds stable?
• It has not net charge
• The octet rule is satisfied
• It has no free electrons
Fig 2.12
Fig 2.13
Important Properties of Water
•
•
•
•
•
Cohesion (liquid) / Adhesion (polarity)
High Specific Heat (maintain temperature)
High Heat of Vaporization (cools body)
Lower Density of Ice (water bodies)
High Polarity / Water as a Solvent
Fig 2.14
Fig 2.15
Fig 2.16
Fig 2.17
Water Ionizes
• Water dissociates and releases hydrogen
ions (H+) and hydroxide ions (OH-).
• Concentrations of hydrogen ions or hydroxide
ions can be represented using the pH scale.
moles/liter
1 x 10 –6 [H+] = pH 6
1 x 10 –7 [H+] = pH 7
1 x 10 –8 [H+] = pH 8
*A mole is the atomic weight of a molecule weighed out
in grams. Atomic weight of H+ is one.
pH
Concentration of H+
pH 0 = 1x10-0
pH 1 = 1x10-1
pH 2 = 1x10-2
pH 3 = 1x10-3
pH 4 = 1x10-4
pH 5 = 1x10-5
pH 6 = 1x10-6
pH 7 = 1x10-7
pH 8 = 1x10-8
pH 9 = 1x10-9
pH 10 = 1x10-10
pH 11= 1x10-11
pH 12 = 1x10-12
pH 13 = 1x10-13
pH 14 = 1x10-14
1
0.1
0.01
0.001
0.0001
0.00001
0.000001
0.0000001
0.00000001
0.000000001
0.0000000001
0.00000000001
0.000000000001
0.0000000000001
0.00000000000001
• Acids are molecules that release
hydrogen ions in solution (usually
water).
HCl  H+ + Cl•Bases are molecules that either take up
hydrogen ions or give off hydroxide ions
in solution.
NaOH  Na+ + OHHydroxide ion
Fig 2.18
• Buffers are substances that help to resist
change in pH. Buffers will take-up/remove
excess hydrogen ions (H+) or hydroxide (OH-)
ions.
When hydrogen ions are added to
solution the following reaction occurs:
H+ + HCO3¯  H2CO3
When hydroxide ions are added to
solution the following reaction
occurs:
OH ¯ + H2CO3  HCO3¯ + H2O
Fig 2.20
Fig
2.19