1/7/2015
A Recipe for Compounds
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.
Dinitrogen Trioxide
N2O3
Magnesium Chloride
MgCl2
Unit 7: Chemical Formulas and
Compounds
Lesson #7.2: Naming/ Writing
Formulas for Binary/Ternary
Formulas
38
37
Binary Compounds
Binary Compounds
Compounds made of TWO elements.
The cation (metal) is written first, followed by
the anion (nonmetal).
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)
We use subscripts to show the number of each
atom in the compound.
We never use the subscript 1 (it is assumed)
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.
39
Examples
40
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.
41
1
1/7/2015
Writing Formulas for Binary
Ionic Compound
Writing Formulas of Binary
Ionic Compound
Example: Iron (III) chloride (note the 2 word name)
1. Write the formulas for the cation
and anion, including CHARGES!
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.
Al3+2 S2-3
3. Balance charges , if necessary,
using subscripts. Use the crisscross method to balance the
subscripts.
2.
Now balanced.
Not balanced!
Fe3+ Cl-
3
Check to see if charges
are balanced.
Now balanced.
3. Balance charges , if necessary,
using subscripts. Use the crisscross method to balance the
subscripts.
= Al2S3
Not balanced!
= FeCl3
Roman Numerals
Naming Binary Compounds
If the cation (metal) is type I – has only one
possible oxidation state, it is given its normal name.
If the cation (metal) is type II - has more than one
possible oxidation state, we indicate the oxidation
state it has by using the stock system (put the
oxidation state in a roman numeral after its name).
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
The anion (nonmetal) has the end of its name
changed to “-ide”.
It has the first negative charge listed on the Periodic
Table.
45
Name These:
KCl
ZnO
FeBr3
Ag2S
Cr2O3
CrO3
Ca3P2
CuS
Cu2S
•
•
•
•
•
•
•
•
•
Formulate These
Potassium Chloride
Zinc Oxide
Iron (II) Bromide
Silver Sulfide
Chromium (III) Oxide
Chromium (VI) Oxide
Calcium Phosphide
Copper (II) Sulfide
Copper (I) Sulfide
Potassium Sulfide
Cobalt (II) Oxide
Cobalt (III) Oxide
Tin (II) Sulfide
Tin (IV) Sulfide
Calcium Phosphide
Aluminum Bromide
Silver Nitride
47
•
•
•
•
•
•
•
•
K2S
CoO
Co2O3
SnS
SnS2
Ca3P2
AlBr3
Ag3N
48
2
1/7/2015
More About Polyatomic Ions
Ternary Compounds
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
49
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.
51
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.
50
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
Ammonium Sulfide
Cobalt (II) Cyanide
Cobalt (III) Sulfate
Tin (II) Nitrate
Tin (IV) Nitrate
Calcium Phosphate
Aluminum Dichromate
Silver Nitrite
•
•
•
•
•
•
•
•
(NH4)2S
Co(CN)2
Co2(SO4)3
Sn(NO3)2
Sn(NO3)3
Ca3(PO4)2
Al2(Cr2O7)3
AgNO2
54
3
1/7/2015
Name These:
•
•
•
•
•
•
•
•
•
•
KNO3
ZnSO4
Fe(NO2)2
Fe(NO2)3
Ag2CO3
Cr2(SO3)3
Cr(SO3)3
Ca3(PO4)2
CuCrO4
Cu2CrO4
Molecular Compounds
Potassium Nitrate
Zinc Sulfate
Iron (II) Nitrite
Iron (III) Nitrate
Silver Carbonate
Chromium (III) Sulfite
Chromium (IV) Sulfite
Calcium Phosphate
Copper (II) Chromate
Cooper (I) Chromate
Molecular compounds are made of nonmetals, only.
Two ways to name them:
1. The stock system:
The atom with the lower Eneg is written first. Write the
charge of that atom using a roman numeral.
2. The Prefix System:
1. Use prefixes (mono-, di-, tri-, tetra-) to describe how
many atoms of each element are found in the
molecule. Don’t use “mono-” if there is one of the
first element in the formula
55
56
Try Some
Molecular Formula:
Carbon(IV)CO
Oxide
2
Carbon (II) CO
Oxide
Nitrogen(IV)Oxide
NO2
Nitrogen(VI)Oxide
NO3
Nitrogen(V)Oxide
N2O5
Sulfur(II)Oxide
SO
Sulfur(VI)Oxide
SO3
Carbon(IV)Chloride
CCl4
Phosphorous(III)Oxide
P2O3
Nitrogen(III)Oxide
NCl3
Stock System
• Prefix System
Carbon Dioxide
Carbon Monoxide
Nitrogen Dioxide
Nitrogen Trioxide
Dinitrogen Pentoxide
Sulfur Monoxide
Sulfur Trioxide
Carbon Tetrachloride
Diphosphorous Trioxide
Nitrogen Trichloride
58
NOTE!!!!!
Molecular Compounds:
Prefix System or Stock System is fine
Any
Questions?
Ionic Compounds:
Stock System ONLY!!!
NO PREFIX SYSTEM!!!
EVER!!!!
WHO WILL BE THE FIRST TO FORGET THIS?!?!
What now?
59
60
4