Mission B5
- How do you Name
and Write
chemical formulas
for Compounds?
“Not Just
James Bond”
Part 1 - Naming Binary Compounds
• Binary compounds – elements with only two
types of atoms in it
• Naming binary compounds is simple
– It is based on the names of the cations and
anions and all binary compounds end in -ide
• Examples:
–
–
–
–
NaCl =
CaF2 =
Al2O3 =
BaO =
sodium chloride
calcium fluoride
aluminum oxide
barium oxide
Part 2 - Naming Transition Metal Compounds
• Similar to naming binary compounds
• But transition metals have multiple oxidation
states (can have different charges)
• Steps
– determine the oxidation number of the
nonmetal
– use the rules of oxidation states to solve
– determine the oxidation number of the
nonmetal
– The name must have Roman numerals to
show the oxidation state of the metal
Example: CuCl2
• Step 1
– determine the charge on the chlorine
– Chlorine has a higher EN therefore will be a
negative oxidation state which is -1
– But there are two chlorines so the total is -2
• Step 2
– Determine the charge on the copper
– The compound’s total charge must equal zero
– Copper must be a +2 charge to balance the
chlorine
• Therefore CuCl2 is called copper II chloride
Example: In FeCl3
Step 1
– what is the charge on the chlorine?
-1 = it has the higher electronegativity and is
negative
– What is the total charge of 3 chlorines?
-3 = 3 x -1
Step 2
– what is the charge on FeCl3?
Zero = charges in compounds add up to 0
– What is the charge on the iron then?
+3 = chlorine’s -3 + iron’s +3 = 0
What is the name of the particle FeCl3 then?
– iron III chloride = “III” shows the iron’s charge
Part 3 - Naming Polyatomic Compounds
• Polyatomic ions
– Groups of atoms that have a
collective charge on them
– See CRTable E
– Similar to binary naming
– If more than two elements in the
compound, look up the
polyatomic ion on Table E
– Example
[Na]+ + [SO4] 2- Na2SO4
sodium + sulfate = sodium sulfate
Naming Polyatomic Compounds
• Examples
• Na2CO3
= sodium carbonate
• HCN
= hydrogen cyanide
• KClO3
= potassium chlorate
• NH4Cl
= ammonium chloride
Part 4 - Naming Molecular Compounds
• Naming molecular
compounds
(covalently bonded
substances) is similar to
naming ionic ones with
one exception:
– When naming
substances with all
nonmetals
– Prefixes are used to
designate the
number of atoms of
each
Prefix
# of Formula
Atoms example
Name
mono
1
CO
Carbon
monoxide
di
2
CO2
Carbon
dioxide
tri
3
SO3
Sulfur trioxide
tetra
4
CCl4
Carbon
tetrachloride
penta
5
PCl5
Phosphorus
pentaflouride
Examples of Naming Covalent Compounds
• Examples:
– CO - carbon monoxide
– CO2 - carbon dioxide
– SO2 - sulfur dioxide
– N2O3 - dinitrogen trioxide
– SF6 - sulfur hexafluoride
– H2O - dihydrogen monoxide
Writing Formulas
• When writing chemical formulas
• Reverse the rules for writing chemical
names
• Here are examples of each type of chemical
formula
• Ex 1 - Binary compound - sodium chloride
– sodium’s oxidation number is Na+1
– chlorine’s oxidation number is Cl-1
– Charges are equal and cancel each other
– Therefore the chemical formula = NaCl
Writing Chemical Formulas
• Ex 2 - Binary compound - aluminum chloride
–
–
–
–
one aluminum has is Al+3
one chlorine is ClIt takes one Al+3 to balance the charge of three ClTherefore the formula for aluminum chloride is
AlCl3
• Ex 3 - Transition metals – iron II oxide
– one iron II has a charge of Fe+2
– one oxygen has a charge of O-2
– The two charges balance out to a 1:1 ratio
– Therefore the formula for iron II oxide is FeO
Writing Chemical Formulas
• Ex 4 - Nonmetal-nonmetal compounds dinitrogen trioxide
– Oxidation numbers aren’t required in writing
this formula
– Dinitrogen is two nitrogens
– Trioxide is there oxygens
– Therefore the formula for dinitrogen trioxide
is N2O3
Writing Chemical Formulas
• Ex 5 - Polyatomic ions –
magnesium nitrate
– Magnesium (Mg+2) is in Group 2 and has
a +2 oxidation charge
– Nitrate (NO3-) is a polyatomic ion from
Table E with an oxidation number of -1
– So two nitrates are needed to balance
the one magnesium and give a zero
charge
– Therefore the formula for magnesium
nitrate is Mg(NO3)2
Writing Chemical Formulas
• Ex 6 - Polyatomic ions and transition
metals – copper I sulfate
– Copper (Cu+1) has a +1 charge as per the
Roman numeral
– Sulfate (SO4-2) is a polyatomic ion from
Table E with an oxidation number of -2
– So two coppers are needed to balance
the one sulfate and give a zero charge
– Therefore the formula for copper I sulfate
is Cu2 SO4
Writing Chemical Formulas
• A short cut – the Criss-Cross method of
writing
– Look at the oxidation states of the elements
in the compound
– cross the numbers, drop the charges, and
you will have the formula
– Example – lead II chloride
• Lead
+2 charge
• Chlorine
-1 charge
Pb +2
Cl -1 
Pb1Cl2