Transcript +6 - C7Chemistry

Naming Binary
Compounds
Containing a Metal
and a Nonmetal
Pisgah High School
M. Jones
The Stock System
Named for Alfred Stock, a
German chemist and teacher who
published the system in 1919.
Add a Roman numeral after
the name of the metal to
indicate the oxidation number.
Using the Stock System:
1. Write the name of the metal
2. Add a Roman numeral
corresponding to the oxidation
number of the metal (if necessary)
3. Write the name of the negative
element, modified to end in -ide
When is the Roman Numeral
Necessary?
When the metal has more than one
oxidation number.
Metals in groups IA, IIA, and III B
do not need Roman numerals.
In addition, omit the Roman numeral
for Al, Ga, In, Zn, Cd and Ag.
What is an oxidation number?
The oxidation number is a
number that tells us how an
element combines with other
elements.
For ions, the
oxidation number is
the ionic charge.
What does the Roman Numeral do?
The Roman numeral indicates the
oxidation number on a single metal
atom, and differentiates between
several possible compounds.
Consider: FeO and Fe2O3
Both contain iron and oxygen
But, both cannot be iron oxide …
What does the Roman Numeral do?
Therefore…
FeO is called iron(II) oxide and
Fe2O3 is called iron(III) oxide.
Consider: FeO and Fe2O3
Both contain iron and oxygen
But, both cannot be iron oxide …
First, determine the oxidation
number of iron in FeO …
… by starting with the negative
element, find the oxidation number
of the positive element.
Since iron has an oxidation
number of +2, FeO is named
iron(II) oxide.
Then for Fe2O3…
First, determine the oxidation number
of iron in Fe2O3 …
… by starting with the negative
element, find the oxidation
number of the positive element.
Since iron’s oxidation number is +3,
Fe2O3 is named iron(III) oxide.
Remember …
The Roman numeral indicates the
oxidation number of the metal.
You need not use a Roman
numeral for metals in groups
IA, IIA and IIIA,
or for Al, Ga, In, Zn, Cd or Ag
Name these compounds:
SrO
Srontium oxide
CrCl3 Chromium(III) chloride
ZnS
Zinc sulfide
Mn2O3 Manganese(III) oxide
SnF4 Sin(IV) fluoride
TiS2
Titanium(IV) sulfide
Writing formulas for
binary compounds of a
metal and a nonmental
The sum of the oxidation numbers
on all the atoms in a compound
must equal zero.
Consider iron(II) oxide.
Oxygen is –2
+2 –2 = 0
and iron is +2.
FeO
The sum is 0.
Now consider iron(III) oxide
+3 -2
Fe2O3
In iron(III) oxide,
the iron is +3 and
the oxygen is –2.
These don’t add up to zero.
Now consider iron(III) oxide
But, since there
+6 -6 = 0
are two Fe atoms
+3 -2
and
three
O
atoms,
Fe2O3
we can multiply to
2x3=6
get the totals.
3 x –2 = -6
Now the sum is
zero.
Look at it another way:
+6 –6 = 0
-6
+6
+3
+3
-2
-2
-2
Fe2O3= Fe Fe O O O
Now you are ready to
write formulas
The Crisscross Method
Simple but effective…
…most of the time.
Be aware of the potential
problems with this
method.
Suppose you are writing the formula
for copper(II) chloride
First, write down
the symbols:
Cu Cl
Then write the oxidation numbers in
copper(II) chloride
The oxidation
number of
copper comes
+2
from the
name.
Get the
oxidation
number of
-1
chlorine
from the
periodic table.
Cu Cl
Crisscross the numbers for the
formula of copper(II) chloride
When you crisscross,
ignore the signs.
+2
-1
Cu1 Cl 2
Clean up the subscripts in the
formula of copper(II) chloride
Subscripts of 1 are invisible.
(don’t even put the 1)
+2
-1
Cu1 Cl 2
Clean up the subscripts in the
formula of copper(II) chloride
Subscripts of 1 are invisible.
(don’t even put the 1)
+2
-1
Cu Cl 2
Now you have the formula of
copper(II) chloride
Cu Cl 2
When is the “crisscross
method” a problem?
When all the subscripts
are divisible by a number
other than 1.
Look at chromium(VI) oxide
The
oxidation +6
number
of Cr is
+6
-2
Cr O
Oxygen is
always -2
Look at chromium(VI) oxide
Now, crisscross the oxidation
numbers. +6
-2
Cr2O6
When you crisscross, both
subscripts are divisible by 2.
Look at chromium(VI) oxide
Divide each subscript by 2.
+6
-2
Cr__2O__6
2
2
Look at chromium(VI) oxide
This is the correct formula
Cr O3
Remember, 1’s are invisible.
Remember: reduce the
subscripts to their smallest
whole-number values.
Unless there’s a really
good reason not to.
Some Exceptions:
N2O4
C2H6
P4O10
Hg2Cl2
C6H6
H2O2
The “ic/ous” System
The “ic/ous” method …
… is an archaic method, but still in
use today by the chemical industry
… uses the –ic or –ous suffixes
on the name of the metal.
… may use the Latin name
… uses prefixes like hypo- & per-
Higher oxidation number
Use “ic” for the
higher oxidation
number, like
ferric.
IC
OUS
Use “ous” for the
lower oxidation
number, like
ferrous.
Lower oxidation number
Name and
Latin Root
Lower Ox.
Number
Higher Ox.
Number
iron
ferrous
ferric
2+
3+
ferrum
Fe
Fe
copper
cuprous
cupric
cuprum
Cu+
Cu2+
mercury mercurous mercuric
2+
2+
Hg2
Hg
Examples …
FeCl2
CuO
FeN
Cu3P
HgS
Hg2Cl2
Ferrous chloride
Cupric oxide
Ferric nitride
Cuprous phosphide
Mercuric sulfide
Mercurous chloride
Write the formula …
Ferric bromide
Cupric nitride
Ferrous chloride
Mercuric oxide
Mercurous iodide
Stannous fluoride
FeBr3
Cu3N2
FeCl2
HgO
Hg2I2
SnF2
Mike Jones
Pisgah High School
Canton NC
[email protected]
Copyright 2012
All rights reserved.