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TORTORA • FUNKE
• CASE
Microbiology
AN INTRODUCTION
EIGHTH EDITION
B.E Pruitt & Jane J. Stein
Chapter 2, part A
Chemical Principles
Chemistry
• Chemistry is the study of interactions between
atoms and molecules.
• The atom is the smallest unit of matter that
enters into chemical reactions.
• Atoms interact to form molecules.
The Study of Atoms
Atoms are composed of
• Electrons: negatively charged particles, no weight
• Protons: positively charged particles, 1 amu
• Neutrons: uncharged particles, 1 amu
• Amu = atomic mass unit 6 X 1023 = 1 gram
Atomic weight is the weight of the atom - the sum of it’s
parts: protons and neutrons
Atomic number is the number of protons.
The Study of Atoms
• Protons and neutrons are in the nucleus.
• Electrons move around the nucleus.
Figure 2.1
Chemical Elements
• Each chemical element has a different number of
protons - it’s atomic number.
• Isotopes of an element are atoms with different
numbers of neutrons than typical for that atom.
Carbon 14 versus 12. Isotopes of oxygen are:
16
8
O
17
8
O
18
8
O
Table 2.1
Electronic Configurations
• Electrons are arranged in electron shells
corresponding to different energy levels.
Electronic Configurations
Table 2.2.1
Electronic Configurations
Table 2.2.2
How Atoms Form Molecules: Chemical Bonds
• Atoms combine to complete the outermost shell.
• The number of electrons in this shell is the valence.
How Atoms Form Molecules: Chemical Bonds
• A compound contains different kinds of atoms.
H2O
• The forces holding atoms in a compound are chemical
bonds.
Types of bonds:
• Ionic - exchange of electronics making ions
• Covalent - shared electrons
• Polar unequal sharing
• Hydrogen bonds - between molecules
How Atoms Form Molecules: Chemical Bonds
• The number of protons and electrons is equal in a
neutral atom.
• Ions are atoms that have gained or lost electrons and
are charged.
Figure 2.2a
Ionic Bonds
• Ionic bonds are attractions between ions of opposite
charge. One atom loses electrons and another gains
electrons.
Figure 2.2b
Covalent Bonds
• Covalent bonds form when two atoms share one or
more pairs of electrons.
Figure 2.3a
Hydrogen Bonds
• Hydrogen bonds
form when a
hydrogen atom
covalently bonded to
an O or N atom in
another molecule.
Figure 2.4
Molecular Weight and Moles
• The sum of the
atomic weights in a
molecule is the
molecular weight.
• One mole of a
substance is its
molecular weight in
grams.
H2O
2H
=21
=2
O
= 16
MW
= 18
1 mole weighs 18 g
Chemical Reactions
• Chemical reactions involve the making or breaking of
bonds between atoms.
• A change in chemical energy occurs during a chemical
reaction.
• Endergonic reactions absorb energy.
• Exergonic reactions release energy.
Synthesis Reactions
• Occur when atoms, ions, or molecules combine to form
new, larger molecules
A
Atom, ion,
or molecule A
+
B
Atom, ion,
or molecule B

AB
New molecule
AB
• Anabolism is the synthesis of molecules in a cell.
Decomposition Reactions
• Occur when a molecule is split into smaller molecules,
ions, or atoms.
Breaks
down into
AB
New molecule
AB

A
Atom, ion,
or molecule A
+
B
Atom, ion,
or molecule B
• Catabolism is the decomposition reactions in a cell.
Exchange Reactions
• Are part synthesis and part decomposition.
NaOH +
HCl  NaCl
+ H2O
Reversible Reactions
• Can readily go in either direction.
• Each direction may need special conditions.
Heat
A
+ B
 AB

Water