11/22/2015
A Recipe for Compounds
Unit 6: Part I – Ionic and
Metallic Bonding
Lesson #6.3: Naming/ Writing
Formulas for Binary/Ternary
Compounds
Magnesium Chloride
MgCl2
Writing Compounds
Compounds:
Substances made of two or more elements
chemically bonded together.
Compound Formulas and names follow specific
rules.
You need to know how to write compounds’
formulas and names.
55
54
Binary Compounds
Formulas for Ionic Compounds (cont.)
• A formula unit represents the simplest ratio of
the ions involved.
Compounds made of TWO elements.
The formula of a binary ionic compound is
always the simplest whole-number ratio it can
be (a.k.a. empirical formula or formula unit)
• Monatomic ions are one-atom ions.
The ratio of the elements in the compound has
to be such that the sum of the oxidation states
of the elements is ZERO = the compound is
neutral.
56
Formulas for Ionic Compounds (cont.)
• Oxidation number, or oxidation state, is the
charge of a monatomic ion (common oxidation
states are listed
• on the Periodic
• Table).
Formulas for Ionic Compounds (cont.)
• Polyatomic ions are ions made
up of more than one atom.
• Never change subscripts of
polyatomic ions, place in
parentheses and write the
appropriate subscript outside the
parentheses.
1
11/22/2015
Formulas for Ionic Compounds
Formulas for Ionic Compounds (cont.)
• Chemists around the world need to communicate
with one another, so a standardized system of
naming compounds was developed.
• The symbol for the cation is always written
first, followed by the symbol of the anion.
• Subscripts represent the number of ions of
each element in an ionic compound.
• When writing names and formulas for ionic
compounds, the cation (metal) always appears
first followed by the anion (nonmetal).
• The total charge must equal zero in an ionic
compound.
• We use subscripts to show the number of each
atom in the compound.
• We never use the subscript 1 (it is assumed)
Examples
Writing Formulas – The Criss-Cross Method
X = metal (cation) Y = nonmetal (anion)
• Because compounds are electrically neutral, one
can determine the formula of a compound this
way:
– The charge on the cation becomes the subscript on
the anion.
– The charge on the anion becomes the subscript on the
cation.
– If these subscripts are not in the lowest whole-number
ratio, divide them by the greatest common factor.
62
Writing Formulas for Binary
Ionic Compound
Writing Formulas of Binary
Ionic Compound
Example: Aluminum sulfide (note the 2 word name)
1. Write the formulas for the cation
and anion, including CHARGES!
2. Check to see if charges are
balanced.
3. Balance charges , if necessary,
using subscripts. Use the crisscross method to balance the
subscripts.
Al3+2 S2-3
Now balanced.
Not balanced!
= Al2S3
Example: Iron (III) chloride (note the 2 word name)
1. Write the formulas for the cation
and anion, including CHARGES!
2.
Check to see if charges
are balanced.
3. Balance charges , if necessary,
using subscripts. Use the crisscross method to balance the
subscripts.
Fe3+ Cl-
3
Now balanced.
Not balanced!
= FeCl3
2
11/22/2015
Ternary Compounds
More About Polyatomic Ions
1. They are all made of
more than one atom.
2. Most of them have
negative charges.
3. Most of them contain
Oxygen.
4. The positive ones end
in –ium. The negative
ones end in –ide (two
atoms), -ite (less O’s),
or –ate (more O’s).
Ionic Compounds that
contain at least one
POLYATOMIC ion.
Polyatomic Ion:
Ion made from two or
more atoms that are
covalently bonded
These are listed on
Reference Table E
66
Writing Formulas for Ternary Compounds
Pretty much the same rules. Some
modifications:
1. If there is more than one polyatomic ion in
the compound, you need a parentheses and a
subscript that goes outside the parenthesis.
2. + ion keeps it’s name and uses the stock
system if necessary.
3. - ion keeps its name if it is a polyatomic ion.
68
Writing Formulas for Ternary Ionic
Compound
Example: Ammonium sulfate (note the 2 word name)
1. Write the formulas for the
cation and anion,
including CHARGES!
2. Check to see if charges
are balanced.
( NH4+) SO422
Now balanced.
Not balanced!
= (NH4)2SO4
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.
67
Writing Formulas For Ternary Ionic
Compound
Example: Barium nitrate (note the 2 word name)
1. Write the formulas for the
cation and anion, including
CHARGES!
2. Check to see if charges are
balanced.
Ba2+ ( NO3- ) 2
Now balanced.
Not balanced!
3. Balance charges , if necessary,
using subscripts. If you need
more than one of a polyatomic
ion, put parentheses around the
ion’s formula. Use the criss-cross
method to balance subscripts.
= Ba(NO3)2
Formulate These
Potassium Sulfide
Cobalt (II) Oxide
Cobalt (III) Oxide
Tin (II) Sulfide
Tin (IV) Sulfide
Calcium Phosphide
Aluminum Bromide
Silver Nitride
•
•
•
•
•
•
•
•
K2S
CoO
Co2O3
SnS
SnS2
Ca3P2
AlBr3
Ag3N
71
3
11/22/2015
Names for Ions and Ionic Compounds (cont.)
Formulate These
Ammonium Sulfide
Cobalt (II) Cyanide
Cobalt (III) Sulfate
Tin (II) Nitrate
Tin (IV) Nitrate
Calcium Phosphate
Aluminum Dichromate
Silver Nitrite
•
•
•
•
•
•
•
•
• Chemical nomenclature is a systematic way of
naming compounds.
(NH4)2S
Co(CN)2
Co2(SO4)3
Sn(NO3)2
Sn(NO3)3
Ca3(PO4)2
Al2(Cr2O7)3
AgNO2
– Name the cation followed by the anion.
– For monatomic cations with one oxidation state , use
the element name.
– For monoatomic cation with multiple oxidation states of
the same element, the oxidation state is written in
parentheses after the name of the cation.
– For monatomic anions, use the root element name and
the suffix –ide.
– When the compound contains a polyatomic ion, name
the cation followed by the name of the polyatomic ion.
72
Roman Numerals
Names for Ions and Ionic Compounds (cont.)
Standard Number
Roman Numeral
Standard Number
Roman Numera
1
2
3
4
5
I
II
III
IV
V
6
7
8
9
10
VI
VII
VIII
IX
X
Name These:
KCl
ZnO
FeBr3
Ag2S
Cr2O3
CrO3
Ca3P2
CuS
Cu2S
•
•
•
•
•
•
•
•
•
Name These:
Potassium Chloride
Zinc Oxide
Iron (III) Bromide
Silver Sulfide
Chromium (III) Oxide
Chromium (VI) Oxide
Calcium Phosphide
Copper (II) Sulfide
Copper (I) Sulfide
KNO3
ZnSO4
Fe(NO2)2
Fe(NO2)3
Ag2CO3
Cr2(SO3)3
Cr(SO3)3
Ca3(PO4)2
CuCrO4
Cu2CrO4
76
•
•
•
•
•
•
•
•
•
•
Potassium Nitrate
Zinc Sulfate
Iron (II) Nitrite
Iron (III) Nitrite
Silver Carbonate
Chromium (III) Sulfite
Chromium (VI) Sulfite
Calcium Phosphate
Copper (II) Chromate
Cooper (I) Chromate
77
4
11/22/2015
Lesson 6.3 Assessment
Lesson 6.3 Assessment
What is the name of the compound
Ca(OH)2?
D
0%
A. A
B. B
C. C
D.0% D0%
0%
C
calcium oxide
calcium(I)oxide
calcium hydroxide
calcium peroxide
A
D
A
0%
A. A
B. B
C. C
0%
0%
0%
D. D
C
1 and 2
2 and 1
2 and 3
1 and 1
B
A.
B.
C.
D.
A.
B.
C.
D.
B
Which subscripts would you most likely
use for an ionic compound containing an
alkali metal and a halogen? (Remember,
1 = no written subscript)
5