Sections 9.1 & 9.2
NAMING IONS &
FORMULAS FOR
IONIC COMPOUNDS
Type of Ion Formed
• Remember that 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
Forming an Ion
• Remember
that ions are
different in
size from the
atomic form
of the
element. This
affects
crystalline
structure, but
not ratios in
formulas.
Review of 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
easy to
predict.
Several will
readily form
more than one
type of ion.
Roman
numerals also
are part of •
their names.
Others to know are silver (Ag+), gold
(Au+), zinc (Zn2+) and cadmium (Cd2+).
Review: Naming 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.
• Group 4A and 8A tend not to form ions.
Transition Metal Ion Use
• The transition metal
compounds are frequently
very bright in color, so they are
frequently used as pigments
(to color other materials).
• For example:
• chromium compounds are used to make yellow,
orange, red or green paints.
• Cadmium compounds produce colors from yellow to
red to maroon.
Practice
Write the symbol (including the charge) for the ion
formed by each element and then name the ion
and classify it as an anion or a cation:
Arsenic
Beryllium
Astatine
Gallium
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 –
these are tightly bound groups of atoms that
behave as a unit and carry a charge.
• Most polyatomic ions are anions and usually
end in “ite” or “ate;” however, there are some
exceptions to this rule.
Polyatomic Suffixes
• The two exceptions included
in the table are cyanide and
hydroxide.
• You may also encounter a
couple of polyatomic cations,
which end in “ium”: the
ammonium ion (NH4+) and
hydronium ion (H3O+).
• You should study your ion
flashcards again this chapter.
Polyatomic Suffixes
• One thing you may notice about
polyatomic anions ending in “ite”
or “ate” is that they always refer
to anions containing oxygen.
• The “ite” suffix indicates that the
ion has one less oxygen than a
polyatomic ion with the “ate”
ending (but it doesn’t tell you
how many that is).
Similar Polyatomics
• Notice also that some of these ions
are similar, they just have an H as
part of the formula – think of this as
having a hydrogen ion (H+)
combined with the polyatomic ion
(notice that the anionic charge is
one less when H is part of the
formula – from adding a +1 to the
charge).
• Look at PO43-, HPO42- and H2PO4-.
Classical Naming
• One other thing you should
be aware if is that initially
their naming system differed
from the system we use
today.
• In the “classical” system, the
elements that had more than
one possible charge were
named using “ous” or “ic” as
suffixes, with “ous” being
used on the cation with the
lower charge, as shown in the
table:
Naming Compounds
• Scientists used to make up
their own names for
compounds so its name
described its properties,
source or use:
• Baking soda – used to make
cakes rise when baked
• Plaster of paris – plaster used to
make face masks
Naming Systematically
• Antoine Lavoisier and other chemists
decided to come up with a systematic method
for naming compounds (so they wouldn’t
have to memorize all the names).
• The easiest ones to name are binary ionic
compounds – these consist of two types of
ions joined together: the name of the
compound is just the combination of the ion
names, with the cation name always given
first.
Naming Systematically
• Before we practice naming binary ionic
compounds, first recall that ions will combine
in a way that the result has no charge (the
positive and negative charges will balance).
Sn4+ bound to F- would be: SnF4
This is called: tin(IV) fluoride
Naming Systematically
• Also, you should know that if you wish to
indicate that there are 2 or more units of a
polyatomic ion in one formula unit of the
compound, use parentheses around the
polyatomic ion formula.
• It would take 2 nitrate cations to balance with
one calcium ion in calcium nitrate:
Ca2+ bound to NO3- would be: Ca(NO3)2
Practice Naming Binary Ionic:
NaF
MgCl2
Cs2O
FeCl2
MnF3
CaSO4
Practice Naming Binary Ionic:
Na2CO3
NaHCO3
Cu(NO2)2
KC2H3O2
Zn(OH)2
NH4Cl
Taking it the other way:
• If you know the name of a binary ionic
compound, you can write the formula – just
remember to make sure that your formula has
the proper number of each type of ion to
insure that the charges add to give zero.
• Start with the formulas of the ions involved
along with their charges. Then “crisscross” the
charges to get the subscripts – finish by
making sure the ions are in a simplified ratio in
the formula.
Using the Crisscross Method
• Iron(III) oxide
• Iron(II) oxide
• Cobalt(II) phosphate
• Silver sulfite
• Calcium dihydrogen phosphate
Practice
Write formulas for compounds formed from these
pairs of ions, then name the compounds:
Ba2+, S2-
Li+, O2-
Ca2+, CN-
NH4+, I-
Practice
Write formulas for these compounds:
Sodium iodide
Stannous chloride
Potassium sulfide
Plumbic fluoride
Lithium hydrogen sulfate Chromium(III) nitrite
Review:
• Three things must be considered when
naming ionic compounds:
• The identity of ions
• The order of the names (cation first)
• The possibility that an element may form cations
with more than one charge (so you must use
roman numerals)
• Name FeN, Mg(NO3)2 and (NH4)2C2O4.
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

http://www.behsscience.com/apchem/chapter7/ion_size.jpg

http://www.chemicalregister.com/storefront/cr/3099/f-Pigments.gif

http://3.bp.blogspot.com/-tM9zAA_mvZ0/Td-V4G0HG_I/AAAAAAAAAXE/x_Zx-i-OICo/s1600/baking-795089.JPG

http://images.melissaesplin.com/wp-content/uploads/2009/03/_dsc1749sm.jpg

http://reich-chemistry.wikispaces.com/file/view/HSantoin.jpg/44989145/HSantoin.jpg