Naming Ions, Compounds and
Molecules
Naming Ions
 OBJECTIVES:
 Identify the charges on monatomic
ions by using the periodic table, and
name the ions.
 Define a polyatomic ion and write
the names and formulas of the most
common polyatomic ions.
Atoms and Ions

Atoms are electrically neutral.


Ions are atoms, or groups of atoms,
with a charge (positive or negative)


Because there are the same number of
protons (+) and electrons (-).
They have different numbers of
protons and electrons.
Only electrons can move, and ions are made
by gaining or losing electrons.
An Anion is…



A negative ion.
Has gained electrons (been reduced).
Nonmetals can gain electrons.

Charge is written as a superscript on the right.
1F
2O
Has gained one electron (-ide
is new ending = fluoride)
Gained two electrons (oxide)
A Cation is…
l
l
l
l
A positive ion.
Formed by losing electrons (been
oxidized).
More protons than electrons.
Metals can lose electrons
+
K
2+
Ca
Has lost one electron (no
name change for positive ions)
Has lost two electrons
Predicting Ionic Charges
Group 1:
Lose 1 electron to form 1+ ions
H+
Li+
Na+
K+
Rb+
Predicting Ionic Charges
Group 2:
Loses 2 electrons to form 2+ ions
Be2+ Mg2+ Ca2+ Sr2+ Ba2+
Predicting Ionic Charges
B3+
Al3+
Ga3+
Group 13: Loses 3
electrons to form
3+ ions
Predicting Ionic Charges
Neither! Group 4
elements rarely form
ions (they tend to share)
Group 4: Do they
lose 4 electrons or
gain 4 electrons?
Predicting Ionic Charges
N3-
Nitride
P3-
Phosphide
As3- Arsenide
Group 15: Gains 3
electrons to form
3- ions
Predicting Ionic Charges
O2-
Oxide
S2-
Sulfide
Se2- Selenide
Group 6: Gains 2
electrons to form
2- ions
Predicting Ionic Charges
F- Fluoride
Cl- Chloride
Group 7: Gains
Br- Bromide
1 electron to form
I- Iodide
1- ions
Predicting Ionic Charges
Group 0: Stable
noble gases do not
form ions!
Predicting Ionic Charges
Many transition elements have more than one
possible oxidation state.
Note the use of Roman
Iron (II) = Fe2+
numerals to show charges
Iron (III) = Fe3+
Predicting Ionic Charges
Some of the post-transition elements also
have more than one possible oxidation state.
Tin (II) = Sn2+
Lead (II) = Pb2+
Tin (IV) = Sn4+
Lead (IV) = Pb 4+
Predicting Ionic Charges
Some transition elements have only one
possible oxidation state, such as these three:
Silver = Ag+
Zinc = Zn2+ Cadmium = Cd2+
Naming cations

Two methods can clarify when more than
one charge is possible:
1)
2)
Stock system – uses roman
numerals in parenthesis to indicate
the numerical value
Classical method – uses root word
with suffixes (-ous, -ic)
Naming cations



We will use the Stock system.
Cation - if the charge is always the same (like
in the main group of metals) just write the
name of the metal.
Transition metals can have more than one
type of charge.
 Indicate their charge as a roman
numeral in parenthesis after the name
of the metal
Naming Anions
 Anions are always the
same charge
 Change the monatomic
element ending to – ide
 F a fluorine atom will
become a fluoride ion.
Practice by naming these:





Cl
chloride ion
3N
nitride ion
Br
bromide ion
O23+
Ga
oxide ion
gallide ion gallium ion (not anion)
Write symbols for these:




sulfide ion
iodide ion
phosphide ion
strontium ion
This last one was to see if you were paying
attention. This is a cation and thus stays with the
actual element name, no change in ending!
S2IP3Sr2+
Naming Ionic Compounds
 1. Name the cation first, then anion

2. Monoatomic cation = name of the
element
Ca2+ = calcium ion

3. Monoatomic anion = root + -ide
Cl- = chloride
CaCl2 = calcium chloride
Not all ionic compounds are that
simple…
• Polyatomic ions are groups of atoms
covalently bound, but because of the way they
are together AS A UNIT, they have a charge…
The polyatomic ion
chlorate is chlorine
and oxygen
sharing electrons
but as a group
have a -1 charge.
(more on why this
happens in a few
classes!)
-1
O
Cl
O
O
Polyatomic ions are…

Groups of atoms that stay together and
have an overall charge, and one name.

Acetate (ethanoate):

nitrate:
CH3CO O-

NO3nitrite: NO2-

permanganate: MnO4-

hydroxide:
OH- and cyanide: CN-
(see the common polyatomic ions to know
that I gave you in class.)
Writing Ionic Compound Formulas
Example: Barium nitrate (note the 2 word
name)
1. Write the formulas for the cation and
anion, including CHARGES!
2. Check to see if the charges are balanced.
3. Balance charges , if necessary, using
subscripts. Use parentheses if you need
more than one of a polyatomic ion. Use
the criss-cross method to balance
subscripts. (The charge of the cation becomes the
subscript of the anion, and vise versa, of course, you
don’t have to write the charge or subscript of “1”)
Ba(NO3)2
Writing Ionic Compound Formulas
Example: Ammonium sulfate
1. Write the formulas for the
cation and anion, including
CHARGES!
2. Check to see if charges
are balanced.
NH4 SO42-
3. Balance charges , if necessary,
using subscripts. Use parentheses if
you need more than one of a
polyatomic ion. Use the criss-cross
method to balance the subscripts.
Remember the charge and subscript of “1” are not
actually written in.
+
(NH4)2SO4
Writing Ionic Compound Formulas
Example: Iron (III) chloride
1. Write the formulas for the
cation and anion, including
CHARGES!
Fe3+ Cl-
2. Check to see if charges
are balanced.
3. Balance charges , if necessary,
using subscripts. Use parentheses if
you need more than one of a
polyatomic ion. Use the criss-cross
method to balance the subscripts.
FeCl3
Writing Ionic Compound Formulas
Example: Aluminum sulfide
1. Write the formulas for the
cation and anion, including
CHARGES!
3+
Al
2S
2. Check to see if charges
are balanced.
3. Balance charges , if necessary,
using subscripts. Use parentheses if
you need more than one of a
polyatomic ion. Use the criss-cross
method to balance the subscripts.
Al2S3
Writing Ionic Compound Formulas
Example: Magnesium carbonate
1. Write the formulas for the
cation and anion, including
CHARGES!
2. Check to see if charges
are balanced. (Since they
balance they are in a 1:1
ratio! No need for
subscripts, remember ionic
are shown as the lowest
ratio of atoms.)
Mg2+ CO32MgCO3
Writing Ionic Compound Formulas
Example: Zinc hydroxide
1. Write the formulas for the
cation and anion, including
CHARGES!
2+
Zn
OH
2. Check to see if charges are
balanced.
3. Balance charges , if necessary,
using subscripts. Use parentheses if
you need more than one of a
polyatomic ion. Use the criss-cross
method to balance the subscripts.
Zn(OH)2
Writing Ionic Compound Formulas
Example: Aluminum phosphate
1. Write the formulas for the
cation and anion, including
CHARGES!
2. Check to see if charges are
balanced.
3+
Al
PO4
AlPO4
3-
Naming Ionic Compounds
(Metals with multiple oxidation states)


some metals can form more than one charge
(usually the transition metals)
use a Roman numeral in their name:
PbCl2 – use the anion to find the charge on the
cation (chloride is always 1-)
Pb2+ is the lead (II) cation
PbCl2 = lead (II) chloride
Things to look for:
1)
2)
3)
If cations have ( ), the number
in parenthesis is their charge.
If anions end in -ide they are
probably off the periodic table
(Monoatomic)
If anion ends in -ate or –ite,
then it is polyatomic
Practice by writing the formula
or name as required…





Iron (II) phosphate
Fe3(PO4)2
Potassium sulfide
K2S
Ammonium chromate (NH4)2CrO4
MgSO4
Magnesium sulfate
FeCl3
Iron (III) chloride
Practice by writing the formula
for the following:
 Magnesium hydroxide
 Mg(OH)2
 Iron (III) hydroxide
 Fe(OH)3
 Zinc hydroxide
 Zn(OH)2 (Zinc is always +2, see slide 16)
Hydrates




Some compounds contain H2O in their
structure. These compounds are called
hydrates.
The H2O can usually be removed if heated.
A dot separates water: e.g. CuSO4•5H2O is
copper(II) sulfate pentahydrate.
A Greek prefix indicates the # of H2O groups
 Sodium sulfate decahydrate is
 Na2SO4· 10H2O
• How well do you know your
Greek prefixes?
Prefixes




1: mono
tri
4: tetra
hexa
7: hepta
nona
10: deca
2: di
3:
5: penta
6:
8: octa
9:
Hydrates
Give the name of the following:
1. CuSO4 . 5H2O
• Copper (II) sulfate pentahydrate
2. MgCl2 . 6H2O
•
3.
Magnesium chloride hexahydrate
Na2SO4 . 10H2O
•
Sodium sulfate decahydrate
Write the formula for the following:
1. zinc chloride hexahydrate
ZnCl2 . 6H2O
2. calcium phosphate dihydrate
Ca3(PO4)2 . 2H2O
3. copper (I) chloride pentahydrate CuCl2 . 5H2O
Covalent Bonding
• Covalent Bond:
– a bond formed by the sharing of electrons
between atoms. (does NOT form charges)
– Made up of nonmetals
• Molecule: a neutral group of atoms joined
together by covalent bonds. (Compounds
formed with ionic bonds do NOT have
molecules)
• Molecular Formula: chemical formula for
a molecular compound. It shows how many
atoms of each element a molecule contains.
Molecular Nomenclature
•
Prefix System (binary compounds)
1. Less electronegative
atom comes first.
2. Add prefixes to indicate # of atoms.
Omit mono- prefix on first element.
3. Change the ending of the second
element to -ide.
most
Molecular Nomenclature
PREFIX NUMBER
mono1
di2
tri3
tetra4
penta5
hexa6
hepta7
octa8
nona9
deca10
Naming Covalent Binary Compounds
P2O5 = diphosphorus pentoxide
CO2 = carbon dioxide
CO = carbon monoxide
N2O = dinitrogen monoxide
phosphorous pentachloride = PCl5
dinitrogen tetrahydride = N2H4
dichlorine heptaoxide = Cl2O7
iodine dioxide = IO2
Basic reminders in naming Covalent
Compounds

First name: name of the first element in the
formula



Usually the least electronegative
Requires a prefix if more than one of
them
Second name: ends in –ide

ALWAYS requires a prefix
Now try this on your own. Complete the Chemistry
worksheet on naming compounds you were given
in class and posted in Moodle