Section 7.1
IONS
Understanding the Key
• Valence electrons hold the key to ion
formation.
• Gilbert Lewis formulated the Octet
Rule: elements are more stable if they
find a way to reach 8 electrons (by
filling up to get 8 or emptying out the
valence shell to get an inner shell to
become the new outer shell that is full).
• Helium is the exception to the Octet
Rule.
Showing Valence Electrons
• Lewis Gilbert also created a notation for
showing only the valence electrons of an
atom: electron dot structures (a.k.a. Lewis
dot diagram).
Forming an Ion
• The fewer the valence electrons, the more
likely the atom is to give up electrons (empty
out the valence shell), becoming positive ions
known as cations.
Forming an Ion
• The closer to 8 valence electrons an atom is,
the more likely the atom is to gain more
electrons to try to reach a total of 8, becoming
negative ions known as anions.
Forming an Ion
• The representative elements behave in a
predictable manner when determining the
type of ion they will form.
• The group #
(1A-8A) tells
how many
valence
electrons each
has (except for
helium).
Forming an Ion
Naming Cations
• For metallic elements, naming cations that
are formed is easy. The name of the ion is the
same as the name of the atom, just followed
by the word “ion” or “cation.”
Transition Metal Cations
• Transition
metals are
not as easy
to predict.
Some of
them will
readily form
more than
one type of
ion; these
must be
memorized.
• Others to know are silver (Ag+), gold
(Au+), zinc (Zn2+) and cadmium (Cd2+).
Naming Transition Metal Cations
• Notice that
these cation
names are
followed by
Roman
numerals,
providing a way
to distinguish
them from each
other. (Make
flash cards!)
Forming Anions
• Atoms of
nonmetals and
metalloids
form anions by
gaining enough
electrons to fill
their valence
shell.
• This oxygen atom has room for 2 more valence
electrons to fill the 2nd energy level with 8.
Naming Anions
• How do we name anions?
• The atom name endings
(suffix) is changed to –ide,
and it is followed by either
“ion” or “anion.”
• Fluorine atom becomes a
fluoride ion, sulfur atom
becomes sulfide ion, and
phosphorus atom
becomes phosphide ion.
Getting Some Practice
For the following elements, draw the electron
dot structure. Then, predict the ion it would
form. Finish by naming the ion properly.
• Strontium
• Oxygen
• Cesium
Getting Some Practice
• Boron
• Chlorine
• Arsenic
• Krypton
Breaking the rules
• Why does copper form more than one type of
ion? Consider the following:
This is a
pseudo
noble-gas
configuration
since the
preceding
noble gas,
Argon,
doesn’t have
3d-level
electrons.
Breaking the rules
• If the 2 electrons remained in the 4s sublevel,
then there are 2 valence electrons to lose:
Copper atom
Cu
Copper(II) ion
Cu2+
Many transition
metals have
multiple ions
they can form,
and their reasons
may vary. This
example
demonstrates
that it is possible
since 3d and 4s
are so close in
energy.
Mono- versus Poly• All of these ions we’ve discussed are called
monatomic ions – ions formed when one atom
forms an ion.
• Ions also exist that are polyatomic ions – ions
formed when a group of atoms chemically
bonded together has more or less electrons than
it should.
• Most polyatomic ions are anions, although two
you may encounter are cations: the ammonium
ion (NH4+) and hydronium ion (H3O+).
Common Polyatomic Ions
• You should
make
flashcards of
these
polyatomic
ions to learn
their symbols,
charges and
names.
Common Polyatomic Ions
• You should
make
flashcards of
these
polyatomic
ions to learn
their symbols,
charges and
names.
We will be having a couple of ion quizzes, similar to
the element quizzes, during this chapter.
References

http://www.calzim.com/online/online2_1/class_material/unit1/ion.gif

http://www.roymech.co.uk/images14/lewis_elements.gif

http://www.middleschoolchemistry.com/img/content/multimedia/chapter_4/lesson_6/lewis_dot_table.jpg

http://www.kanescience.com/_images/chem_ionic/sodium_ions.png

http://www.calzim.com/online/online2_1/class_material/unit1/unit1.htm

http://www.personal.kent.edu/~cearley/ChemWrld/compounds/ionictable.gif

http://www.chem.uwec.edu/Chem103_F08_F0F/pages/resources/media/transitions_metal_ions_Silberberg_table_2.4.jpg

http://wps.prenhall.com/wps/media/objects/1053/1078773/tools/HPMP.table.2.4.gif