Writing and Naming
Binary Compounds & Hydrates
You will need:
A periodic table
A list of common polyatomic ions
Patience and understanding
Generic Chemical Formulas
MgCl2
Chemical
symbols
Subscript
Binary Compounds
A chemical compound consisting of two parts, a
CATION (+) and an ANION (-)
Examples:
1. Two elements chemically bonded
2. An element and a polyatomic ion
chemically bonded
3. Two polyatomic ions chemically bonded
Binary Compounds
Have two parts
Left side is the cation
Positively charged
MgCl2
Right side is the anion
Negatively charged
Hydrates
A hydrate is a binary compound that
has water attached to its ions and the
water is a PART of the chemical
formula.
Naming hydrates uses terms that
indicate the number of water molecules.
1
2
3
4
5
6
7
8
9
10
mono
di
tri
tetra
penta
hexa
hepta
octa
nona
deca
Hydrates
CaSO4 • 2 H2O
Calcium sulfate dihydrate
Binary compound
AlO3 • 3 H2O
Aluminum oxide trihydrate
Binary compound
CuSO4 • 5 H2O
Copper (II) sulfate pentahydrate
Binary compound
Writing Binary Formulas
6 Steps
1. Write chemical symbols for cation and anion
2. Add cation and anion oxidation numbers as superscripts
3. Check to see if oxidation numbers add to zero
4. If yes, leave as written
5. If no, make oxidation numbers subscripts
6. Check for lowest whole number ratio
Writing Binary Formulas
Write the formula for sodium chloride.
+
-
3
4
Na Cl
1
Add cation andCheck
anionto
oxidation
see if oxidation
numbers
If yes, leave
as as
Write chemical symbols for the cation and anion
superscripts numbers add to zero
written
2
Writing Binary Formulas
Write the formula for magnesium nitride
+2
-3
Mg3 N 2
1
2
3
4
5
Writing Binary Formulas
Write the formula for hydrogen carbonate
+
-2
H 2 CO3
1
2
3
4
5
Writing Binary Formulas
Write the formula for magnesium phosphate
-3
+2
Mg 3(PO4 ) 2
1
2
3
4
5
Writing Binary Formulas
For transition metals the oxidation number is
given in parentheses, In Roman numerals.
Write the formula for iron (III) oxide.
Fe
+3
O
-2
Fe2 O3
Writing Binary Formulas
For hydrates, that is, binary compounds with water (hydrate)
attached:
nickel (II) sulfate hexahydrate
a. Write the formula of the binary compound (first part) using rules 1-4:
NiSO4
b. Insert a “raised dot” after the binary compound:
NiSO4 ●
c. Use name prefix to note the number of water molecules (hydrates):
NiSO4 ● 6 H2O
Polyatomic Ions (learn these)
Table 4
Name
Ammonium
Acetate
Chlorate
Hydroxide
Nitrate
Carbonate
Sulfate
Phosphate
Page 619
Formula
NH4+
C2H3O2ClO3OHNO3CO32SO42PO43-
More Polyatomic Ions
(learn these, too)
Name
Formula
Hydrogen carbonate
(bicarbonate)
HCO3-
Nitrite
NO2-
Permanganate
MnO4-
Sulfite
SO32-
A quick review of hydrates.
Naming Binary Formulas
Binary Compound = CATION + ANION
First:
Get a periodic table and table of common polyatomic ions
Next: Determine the cation and anion in the compound
Then: Note the cation and apply the 5 naming rules IN ORDER
Naming Binary Formulas
5 Rules that begin with the location or kind of the
CATION
Rule 1. For elements in the first two columns of the periodic table
Rule 2. For elements from group 3 up to the staircase
Rule 3. For elements to the right (above) the staircase
Rule 4. For CATIONS that are polyatomic ions
Rule 5. For hydrates
Naming Binary Formulas – Rule 1
For cations (elements) in the first two columns of the periodic
table:
MgCl2
LiOH
a. Cation: Write the name of the element as the first part of the compound:
magnesium
lithium
b. Anion: Write the name of the element with an ide ending:
magnesium chloride
or
c. Anion: Write the name of the polyatomic ion:
lithium hydroxide
Naming Binary Formulas – Rule 2
For cations (elements) from the third group of the periodic table
up to the “staircase”
FeCl2
Cu2SO4
a. Cation: Name of element with Roman Numeral to show oxidation number:
iron (II)
copper (I)
b. Anion: Name the element with an ide ending:
iron (II) chloride
Exceptions to rule:
or
Ag+1
Zn+2
Cd+2
Al+3
(Use Rule 1)
c. Anion: Name the polyatomic ion:
copper (I) sulfate
Naming Binary Formulas – Rule 3
For cations (elements) to the right (above) the “staircase”
CO2
CO
a. Count the “number” of each element. (C-1, O-2
N4S3
C-1, O-1
N-4, S-3)
b. Use prefixes (mono, di, tri, tetra, penta, hexa, hepta, octa, nona, deca) to
indicate the number of each atom present.
b. Do not use “mono” if there is only one of the first element in the compound.
c.
CO2
CARBON DIOXIDE
N4S3
TETRANITROGEN TRISULFIDE
CARBON MONOXIDE
CO
Naming Binary Formulas – Rule 4
For cations that are polyatomic ions:
NH4Cl
NH4OH
a. Cation: Name the polyatomic ion:
ammonium
ammonium
b. Anion: Name the element with an ide ending:
ammonium chloride
or
c. Anion: Name the polyatomic ion:
ammonium hydroxide
Naming Binary Formulas – Rule 5
For hydrates, that is, binary compounds with water (hydrate)
attached:
NiSO4● 6 H2O
a. Name of the binary compound (first part) using rules 1-4:
nickel (II) sulfate
b. Note the number of water molecules (hydrates) by using prefixes:
nickel (II) sulfate hexahydrate
Rest stop!
Inhale and breathe easy!
The next group of slides goes into some detail
about oxidation numbers in covalent compounds
and in polyatomic ions. For this presentation, a
periodic table that shows electronegativities is
most helpful.
Covalent Compounds
Example: phosphate ion
Electronegativity:
2.1
3.5
-2
P O4
3Polyatomic ion
with a charge = -3
Since oxygen is the more
electronegative element, it will
have its normal oxidation
number.
Covalent Compounds
Example:
+5
-2
P O4
+5
3-
The phosphate ion has a charge
of negative three, so the
oxidation numbers must add up
to the total charge of the ion.
- 8
- 3
Ionic Compounds with Polyatomics
Example:
+2
Ca SO4
This is an ionic compound, so the
charge of the metal cation is its
oxidation number
Ionic Compounds with Polyatomics
Example:
+2
Ca SO4
The anion is a polyatomic ion,
sulfate, and the charge of sulfate
is negative two. So the oxidation
numbers of sulfur and oxygen
must add to -2
Ionic Compounds with Polyatomics
Example:
2.5
+2
3.5
-2
Ca SO4
Oxygen is the more
electronegative of the two, so it
keeps its normal oxidation
number.
Ionic Compounds with Polyatomics
Example:
+6
+2
-2
Ca SO4
Sulfur and the four oxygen atoms
must add to negative two (the
charge of the sulfate anion).
Ionic Compounds with Polyatomics
Example:
Pb(OH)4
This is an ionic compound, so the
charge of the metal cation is its
oxidation number. But this is a
transition metal, so we cannot
know it from its position on the
periodic table.
Ionic Compounds with Polyatomics
Example:
+4
-1
Pb(OH)4
But the anion, the hydroxide ion,
carries a charge of negative one.
All four hydroxides are negative
one, but since the compound is
neutral, the oxidation number of
lead must balance it out.
Ionic Compounds with Polyatomics
Example:
3.5
+4
2.1
-2
Pb(OH)4
Within the anion, oxygen is the
more electronegative of the two
elements, and keeps its normal
oxidation number.
Ionic Compounds with Polyatomics
Example:
+4
-2 +1
Pb(OH)4
Within the hydroxide ion, the
oxygen and hydrogen must add
to the charge of the ion, -1