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Naming Compounds and
Writing Formulas
Periodic Table Recall that the periodic table is more
than a list of elements. Elements are put in columns because of
similar properties. Each column is called a group.
2A
1A
3A4A
5A6A
7A
0Representative Elements
The group A elements
Metals
Transition Metals
The Group B elements
Nonmetals
Metalloids
Systematic Naming There are too many compounds to
remember the names of them all. A compound is made of two or more
elements. The name should tell us how many and
what type of atoms.
Types of Compounds
There are two types of compounds: ionic compounds and molecular compounds.
Ionic Compounds
The simplest ratio of the ions represented in an ionic compound is called a formula unit.
The overall charge of any formula unit is zero.
In order to write a correct formula unit, one must know the charge of each ion.
Atoms and Ions Atoms are electrically neutral. They have the same number of protons
and electrons. Ions are atoms, or groups of atoms,
with a charge. Ions have a different numbers of
electrons.
Anions An anion is a negative ion. An anion has gained electrons. Nonmetals can gain electrons. The charge is written as a superscript
on the right.
F-1 Has gained one electron
O-2 Has gained two electrons
Cations A cation is a positive ion. It is formed by losing electrons. There are more protons than electrons. Metals form cations.
K1+ Has lost one electron
Ca2+ Has lost two electrons
Ionic Compounds
The charges of monatomic ions, or ions containing only one atom, can often be determined by referring to the periodic table or table of common ions based on group number.
The charge of a monatomic ion is equal to its oxidation number.
Charges on Ions For most of the Group A elements, the
Periodic Table can tell what kind of ion they will form from their location.
Elements in the same group have similar properties, including the charge when they are ions.
2+
1+
3+ 3- 2- 1-
Charges on Ions:Oxidation Numbers
Naming Cations
We will use the systematic way. For cations, if the charge is always the
same (Group A) just write the name of the metal.
Naming Cations Transition metals (as well as tin and
lead) can have more than one type of charge.
Indicate the charge with Roman numerals in parenthesis.
Zinc (Zn2+) and silver (Ag1+), although transition metals, only have one possible charge. Roman numerals ARE NOT used for zinc and silver.
Example Li1+
Li is the symbol for lithium.
Lithium is a Group 1A metal, so the charge is always the same. Write the name of the metal.
Li1+ is called the Lithium ion.
Example Sr2+
Sr is the symbol for strontium.
Strontium is a Group 2A metal, so the charge is always the same. Write the name of the metal.
Sr2+ is called the Strontium ion.
Example Fe2+
Fe is the symbol for iron.
Iron is a transition metal, so the charge is not always the same. Write the name of the metal, indicating the charge with Roman numerals in parenthesis.
Fe2+ is called the Iron (II) ion.
Example Pb2+
Pb is the symbol for lead.
Lead is a Group 4A metal, and the charge is not always the same. Write the name of the metal, indicating the charge with Roman numerals in parenthesis.
Pb2+ is called the Lead (II) ion.
Problem Name the following cations.
Ca2+
Sn4+
Calcium ion
Al3+ Aluminum ion
Tin (IV) ion
Problem Name the following ions.
Na1+
Cu1+
Sodium ion
Fe3+ Iron (III) ion
Copper (I) ion
Writing the Formulas for Cations
Write the formula for the metal. If a Roman numeral is in parenthesis
use that number for the charge. Indicate the charge with a superscript.
Writing the Formulas for Cations
If no Roman numeral is given, find the Group A metal on the periodic table and determine the charge from the column number.
Example Nickel (II) ion
Ni is the symbol for nickel.
Nickel is a transition metal, which is the reason why the charge with Roman numerals in parenthesis was included.
The formula for the nickel (II) ion is
Ni2+.
Example Gallium ion
Ga is the symbol for gallium.
Gallium is a Group 3A metal and its charge is always the same (+3).
The formula for the gallium ion is
Ga3+.
Problem Write the formulas for the following
cations.
Copper (II) ion
Magnesium ion
Potassium ion
Mg2+
Cu2+
K1+
Problem Write the formulas for the following ions.
Chromium (VI) ion
Silver ion
Mercury (II) ion
Ag1+
Cr6+
Hg2+
Naming Anions Naming monatomic anions is always the
same. Change the element ending to – ide Example: F1- F is the symbol for fluorine, F1- is
ide.fluor ine.
Example Cl1-
Cl is the symbol for chlorine.
Chlorine is a Group 7A nonmetal, so the charge is always the same (-1).
Cl1- is called the chloride ion.
Example O2-
O is the symbol for oxygen.
Oxygen is a Group 6A nonmetal, so the charge is always the same (-2).
O2- is called the oxide ion.
Problem Name the following anions.
S2- sulfide ion
Br1- bromide ion
N3- nitride ion
Problem Name the following anions.
As3- arsenide ion
Te2- telluride ion
Writing the Formulas for Anions
Write the formula for the nonmetal. Find the Group A nonmetal on the
periodic table and determine the charge from the column number.
Problem Write the formulas for the following anions.
iodide ion I1-
phosphide ionP3-
Problem Write the formulas for the following anions.
selenide ion Se2-
carbide ion C4-
Ionic Compounds
Oxidation numbers can be used to determine the chemical formulas for ionic compounds.
If the oxidation number of each ion is multiplied by the number of that ion present in a formula unit, and then the results are added, the sum must be zero.
Ionic Compounds
In the formula for an ionic compound, the symbol of the cation is written before that of the anion.
Subscripts, or small numbers written to the lower right of the chemical symbols, show the numbers of ions of each type present in a formula unit.
Binary Ionic Compounds
Binary ionic compounds are composed of a metal bonded with a nonmetal.
Name the metal ion using a Roman numeral in parenthesis if necessary.
Follow this name with the name of the nonmetal ion.
Example
Name the following binary ionic compounds.
NaCl Sodium chloride
Ca3P2 Calcium phosphide
Example
Name the following binary ionic compounds.
CuO Copper (II) oxide
SnBr2 Tin (II) bromide
Problem
Name the following binary ionic compounds.
Fe2S3 Iron (III) sulfide
AlF3 Aluminum fluoride
Problem
Name the following binary ionic compounds.
KCl Potassium chloride
Na3N Sodium nitride
Problem
Name the following binary ionic compounds.
CrN Chromium (III) nitride
PbO2 Lead (IV) oxide
Writing Formulas for Binary Ionic Compounds
Write the symbol for the metal. Determine the oxidation number from either the column number or the Roman numeral and write it as a superscript to the right of the metal’s symbol.
Writing Formulas for Binary Ionic Compounds
To the right of the metal’s symbol, write the symbol for the nonmetal. Determine the oxidation number from the column number and write it as a superscript to the right of the nonmetal’s symbol.
Writing Formulas for Binary Ionic Compounds
Example: potassium fluoride
K1+
F1-
Writing Formulas for Binary Ionic Compounds
If the two oxidation numbers add together to get zero, the formula is a one-to-one ratio of the elements.
Writing Formulas for Binary Ionic Compounds
Example: potassium fluoride
K1+
F1-
KF
Writing Formulas for Binary Ionic Compounds
Example: aluminum sulfide
Al3+
S2-
Writing Formulas for Binary Ionic Compounds
If the two oxidation numbers DO NOT add together to get zero, you will need to “criss-cross” the superscripts. These numbers now become subscripts.
Writing Formulas for Binary Ionic Compounds
Example: aluminum sulfide
Al3+
S2-
3+2-
Writing Formulas for Binary Ionic Compounds
Omit all positive and negative signs and omit all 1’s.
Writing Formulas for Binary Ionic Compounds
Example: aluminum sulfide
Al S2 3
Al2S3
Problem
Lithium selenide
Write the formulas for the following binary ionic compounds.
Tin (II) oxide
Li2Se
SnO
Problem
Tin (IV) oxide
Write the formulas for the following binary ionic compounds.
Magnesium fluoride
SnO2
MgF2
Problem
Copper (II) sulfide
Write the formulas for the following binary ionic compounds.
Iron (II) phosphide
CuS
Fe3P2
Problem
Gallium nitride
Write the formulas for the following binary ionic compounds.
Iron (III) sulfide
GaN
Fe2S3
Ternary Ionic Compounds
Ternary ionic compounds are composed of at least 3 elements.
Name the metal ion, using a Roman numeral in parenthesis if necessary.
Follow this name with the name of the polyatomic ion.
Polyatomic ions Polyatomic ions are groups of atoms
that stay together and have a charge. Examples are on page 7 of the
Reference Tables for Chemistry and include:Nitrate NO3
-1
Nitrite NO2-1
Hydroxide OH-1
Ternary Ionic Compounds
There is one polyatomic ion with a positive oxidation number (NH4
+) that
may come first in a compound. Name the ion.
Follow this name with the name of the anion or second polyatomic ion.
Ternary Ionic Compounds
Certain polyatomic ions, called oxyanions, contain oxygen and another element.
Examples Name the following ternary ionic
compounds.LiCN
Fe(OH)3
Lithium cyanide
Iron (III) hydroxide
Examples Name the following ternary ionic
compounds. (NH4)2CO3 Ammonium carbonate
NiPO4 Nickel (III) phosphate
Problems Name the following ternary ionic
compounds.NaNO3 Sodium nitrate
CaSO4 Calcium sulfate
Problems Name the following ternary ionic
compounds.
(NH4)2O Ammonium oxide
CuSO3 Copper (II) sulfite
Writing Formulas for Ternary Ionic Compounds
Write the symbol for the metal or ammonium ion. Write the oxidation number as a superscript to the right of the metal’s/ammonium ion’s symbol.
Writing Formulas for Ternary Ionic Compounds
To the right of the metal’s symbol, write the symbol for the nonmetal or polyatomic ion. Write the oxidation number as a superscript to the right of the nonmetal’s/polyatomic ion’s symbol.
Writing Formulas for Ternary Ionic Compounds
Example: potassium nitrate
K1+
NO3
1-
Writing Formulas for Ternary Ionic Compounds
If the two oxidation numbers add together to get zero, the formula is a one-to-one ratio of the elements.
Writing Formulas for Ternary Ionic Compounds
Example: potassium nitrate
K1+
NO3
1-KNO3
Writing Formulas for Ternary Ionic Compounds
Example: aluminum hydrogen sulfate
Al3+
HSO4
1-
Writing Formulas for Ternary Ionic Compounds
If the two oxidation numbers DO NOT add together to get zero, you will need to “criss-cross” the superscripts. These numbers now become subscripts.
Parentheses are to be placed around polyatomic ions before criss-crossing.
Writing Formulas for Ternary Ionic Compounds
Example: aluminum hydrogen sulfate
Al3+
HSO4
1-
3+1-( )
Writing Formulas for Ternary Ionic Compounds
Omit all positive and negative signs and omit all 1’s.
Writing Formulas for Ternary Ionic Compounds
Example: aluminum hydrogen sulfate
Al(HSO4) 3Al(HSO4)3
Problems Write the formulas for the following
ternary ionic compounds.Ammonium chloride
Ammonium sulfide
NH4Cl
(NH4)2S
Problems Write the formulas for the following
ternary ionic compounds.Barium nitrate
Zinc iodate
Ba(NO3)2
Zn(IO3)2
Problems Write the formulas for the following
ternary ionic compounds.Sodium hypochlorite
Chromium (III) acetate
NaClO
Cr(CH3COO)3
Problems Write the formulas for the following
ternary ionic compounds. Iron (II) dichromate
Mercury (I) bromate
FeCr2O7
HgBrO3
STOP HERE
Molecular Compounds
Writing Names and Formulas
Molecular Compounds
Molecular compounds are made of molecules.
They are made by joining nonmetal atoms together into molecules.
Naming is Easier
A molecular compound’s name tells you the number of atoms through the use of prefixes.
Prefixes
1 mono- 2 di- 3 tri- 4 tetra- 5 penta-
6 hexa- 7 hepta- 8 octa- 9 nona- 10 deca-
Prefixes
The name will consist of two words.
Prefix name prefix name -ide
One exception is we don’t write mono- if there is only one of the first element.
Prefixes
The following double vowels cannot be used when writing names: (oa) (oo)
Example
NO2
There is one nitrogen
mononitrogen
But, you cannot use mono- on the first element, so drop the prefix.
mononitrogen nitrogen
Example
NO2
There are two oxygens
dioxygen
Example
NO2
dioxygen
You need the suffix -ide
dioxygenide
Example
NO2
nitrogen dioxide
Example
N2O
There are two nitrogens
dinitrogen
There is one oxygen
monooxygen
Example
N2O
monooxygen
You cannot run (oo) together, so
monoxygen
Example
N2O
monoxygen
You need the suffix -ide
monoxygenide
Example
N2O
dinitrogen monoxide
Problem
Name the following molecular compounds.
Cl2O7
CBr4
dichlorine heptoxide
carbon tetrabromide
Problem
Name the following molecular compounds.
CO2
BCl3
carbon dioxide
boron trichloride
Naming Molecular Compounds
You will not need to criss-cross oxidation numbers.
Molecular compounds name tells you the number of atoms through the use of prefixes.
Example
diphosphorus pentoxide
The name implies there are 2 phosphorous atoms and 5 oxygens.
P2O5
Example
sulfur hexaflouride
The name implies there is 1 sulfur atom and 6 fluorines.
SF6
Problem
Write the formulas for the following molecules. tetraiodide nonoxide
nitrogen trioxide
I4O9
NO3
Problem
Write the formulas for the following molecules. carbon tetrahydride
phosphorus trifluoride
CH4
PF3
Types of Compounds
Smallest piece
Melting Point
State
Types of elements
Formula Unit Molecule
Metal and nonmetal
Nonmetals
SolidSolid, liquid or gas
High >300ºC Low <300ºC
Ionic Molecular
Acids
Writing Names and Formulas
Acids Acids are compounds that give off
hydrogen ions (H+) when dissolved in water.
Acids will always contain one or more hydrogen ions next to an anion.
The anion determines the name of the acid.
Naming Binary Acids
Binary acids contain hydrogen and an anion whose name ends in –ide.
When naming the acid, put the prefix hydro- and change -ide to -ic acid.
Example HCl
The acid contains the hydrogen ion and chloride ion.
Begin with the prefix hydro-, name the nonmetallic ion and change -ide to -ic acid.
hydrochlorideic acid
Example
H2S The acid contains the hydrogen ion
and sulfide ion.
Begin with the prefix hydro- and name the nonmetallic ion.
hydrosulfide
Example
H2S
The next step is change -ide to -ic acid, but for sulfur the “ur” is added before -ic.
hydrosulfideic acidur
Problem
HF
H3P(hydrophosphoric acid)
(hydrofluoric acid)
Name the following binary acids.
Writing the Formulas for Binary Acids
The prefix hydro- lets you know the acid is binary.
Determine whether you need to criss-cross the oxidation numbers of hydrogen and the nonmetal.
Example
Hydrobromic acid The acid contains the hydrogen ion
and the bromide ion.
Example
Hydrobromic acid
H1+Br1-
The two oxidation numbers add together to get zero.
HBr
Example
Hydrotelluric acid The prefix hydro- lets you know the
acid is binary. The acid contains the hydrogen ion
and the telluride ion.
Example
Hydrotelluric acid
H1+Te2-
The two oxidation numbers do NOT add together to get zero, so you must criss-cross.
H2Te
Problem Write the formulas for the following
binary acids. Hydrocyanic acid HCN
Hydroselenic acid H2Se
Naming Ternary Acids The acid is a ternary acid if the anion
has oxygen in it. The anion ends in -ate or -ite. Change the suffix -ate to -ic acid Change the suffix -ite to -ous acid The hydro- prefix is NOT used!
Example
HNO3
The acid contains the hydrogen ion and nitrate ion.
Name the polyatomic ion and change -ate to -ic acid.
nitrateic acid
Example
HNO2
The acid contains the hydrogen ion and nitrite ion.
Name the polyatomic ion and change -ite to -ous acid.
nitriteous acid
Example
H3PO4
The acid contains the hydrogen ion and phosphate ion.
Name the polyatomic ion and change -ate to -ic acid.
phosphateoric acid
Problem
H2CO3
H2SO4
(carbonic acid)
(sulfuric acid)
Name the following ternary acids.
Problem
H2CrO4
HClO2
(chromic acid)
(chlorous acid)
Name the following ternary acids.
Writing the Formulas for Ternary Acids
The lack of the prefix hydro- from the name implies the acid is ternary, made of the hydrogen ion and a polyatomic ion.
Determine whether you need to criss-cross the oxidation numbers of hydrogen and the polyatomic ion.
Example
Acetic acid
H1+C2H3O21-
The polyatomic ion must end in –ate since the acid ends in -ic.
The acid is made of H+ and the acetate ion.
Example
The two charges when added equal zero.
H1+C2H3O21-
HC2H3O2
Example
Sulfurous acid
Again the lack of the prefix hydro- implies the acid is ternary, made of the hydrogen ion and a polyatomic ion.
Example
sulfurous acid
H1+SO32-
The polyatomic ion must end in –ite since the acid ends in -ous.
The acid is made of H+ and the sulfite ion.
Example
The two charges when added do not equal zero, so you must crisscross the oxidation numbers.
H1+SO32-
Example
Ignore the negative sign and ones are understood.
H1+SO32-
H2SO3
Problem
Write the formulas for the following ternary acids. perchloric acid
HClO4
iodic acid HIO3
Problem
Write the formulas for the following ternary acids. perchloric acid
HClO4
iodic acid HIO3