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
1. Two elements chemically bonded
2. An element and a polyatomic ion chemically bonded
3. Two polyatomic ions chemically bonded
A chemical compound consisting of two parts, a CATION (+) and an ANION (-)
Examples:
Binary Compounds
Have two parts
Left side is the cation
Positively charged
Right side is the anion
Negatively charged
MgCl2
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.
11 monomono
22 didi
33 tritri
44 tetratetra
55 pentapenta
66 hexahexa
77 heptahepta
88 octaocta
99 nonanona
1010 decadeca
Hydrates
CaSO4 • 2 H2O Calcium sulfate dihydrate
CuSO4 • 5 H2O
AlO3 • 3 H2O Aluminum oxide trihydrate
Copper (II) sulfate pentahydrate
Binary compound
Binary compound
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.
Na Cl
1 2 3
+ -
4Write chemical symbols for the cation and anionAdd cation and anion oxidation numbers as superscripts
Check to see if oxidation numbers add to zero
If yes, leave as written
Writing Binary Formulas
Write the formula for magnesium nitride
Mg N
1 2 3 4 5
+2 -3
23
Writing Binary Formulas
Write the formula for hydrogen carbonate
H CO3
1 2 3 4 5
+ -2
2
Writing Binary Formulas
Write the formula for magnesium phosphate
Mg PO4
1 2 3 4 5
+2 -3
23( )
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 Page 619
NameName FormulaFormula
AmmoniumAmmonium NHNH44++
AcetateAcetate CC22HH33OO22--
ChlorateChlorate ClOClO33--
HydroxideHydroxide OHOH--
NitrateNitrate NONO33--
CarbonateCarbonate COCO332-2-
SulfateSulfate SOSO442-2-
PhosphatePhosphate POPO443-3-
More Polyatomic Ions
(learn these, too)
NameName FormulaFormula
Hydrogen carbonateHydrogen carbonate
(bicarbonate)(bicarbonate) HCOHCO33
--
Nitrite Nitrite NONO22--
PermanganatePermanganate MnOMnO44--
SulfiteSulfite SOSO332-2-
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
c. Anion: Write the name of the polyatomic ion:
lithium hydroxide
or
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
c. Anion: Name the polyatomic ion:
copper (I) sulfate
or
Exceptions to rule:
Ag+1 Zn+2
Cd+2 Al+3
(Use Rule 1)
Naming Binary Formulas – Rule 3
For cations (elements) to the right (above) the “staircase”
CO2 CO N4S3
a. Count the “number” of each element. (C-1, O-2 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 N4S3
CARBON DIOXIDE TETRANITROGEN TRISULFIDE
CARBON MONOXIDECO
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
c. Anion: Name the polyatomic ion:
ammonium hydroxide
or
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 CompoundsCovalent CompoundsExample: phosphate ion
P O43-
Since oxygen is the more electronegative element, it will
have its normal oxidation number.
-23.52.1
Polyatomic ion with a charge = -3
Electronegativity:
Covalent CompoundsCovalent CompoundsExample:
P O43-
-2
The phosphate ion has a charge of negative three, so the
oxidation numbers must add up to the total charge of the ion.
+5+ 5
- 8
- 3
Ionic Compounds with PolyatomicsIonic Compounds with PolyatomicsExample:
Ca SO4
This is an ionic compound, so the charge of the metal cation is its
oxidation number
+2
Ionic Compounds with PolyatomicsIonic Compounds with PolyatomicsExample:
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
+2
Ionic Compounds with PolyatomicsIonic Compounds with PolyatomicsExample:
Ca SO4
Oxygen is the more electronegative of the two, so it
keeps its normal oxidation number.
+2 -23.52.5
Ionic Compounds with PolyatomicsIonic Compounds with PolyatomicsExample:
Ca SO4
Sulfur and the four oxygen atoms must add to negative two (the charge of the sulfate anion).
+2 -2+6
Ionic Compounds with PolyatomicsIonic Compounds with PolyatomicsExample:
Pb(OH)4This 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 PolyatomicsIonic Compounds with PolyatomicsExample:
Pb(OH)4But 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.
+4 -1
Ionic Compounds with PolyatomicsIonic Compounds with PolyatomicsExample:
Pb(OH)4Within the anion, oxygen is the more electronegative of the two elements, and keeps its normal
oxidation number.
+4 -2
3.5 2.1
Ionic Compounds with PolyatomicsIonic Compounds with PolyatomicsExample:
Pb(OH)4Within the hydroxide ion, the
oxygen and hydrogen must add to the charge of the ion, -1
+4 -2 +1