Notes on Naming Common Compounds: Ionic, Covalent, Acidic
Naming IONIC COMPOUNDS
1. Name the metal (or cation) first, then name the nonmetal (or anion).
2. The metal ion usually has the same name as the metal atom, the name of the nonmetal ion must have the ending suffix
changed to –ide. (or just the special name of the polyatomic anion such as sulfate, carbonate, etc.)
3. The transition metals often have two or more possible charges so you must also indicate the charge on the ion by using
roman numeral in parenthesis afterward OR by using the suffix –ic added to the latin root word for the higher charge or the
suffix –ous for the lower charge.
MgCl2 = magnesium chloride CuSO4 = copper(II) sulfate; Li2CO3 = lithium carbonate
Predicting Chemical Formulas for IONIC COMPOUNDS
1) Write the symbols for the two ions, placing the cation (the metallic ion) first.
2) Determine the charge on the ions. The three sources to use for this are your memory, the polyatomic ion table, or the
periodic table of elements.
Some good general rules to follow for predicting ionic charges for elements are Column 1 elements always have a +1
charge, Column 2 = +2, Column 17 = -1, Column 16 = -2, and Column 15 = -3.
3) Using the known charges of the ions select subscripts that will make the total positive charge equal to the total negative
charge. A good trick to use: Try the switch method of putting the absolute value of the charge of the anion as the
subscript for the cation and vice versa.
Mg+2 and Br-1 …switch ‘em to predict the chemical formula of MgBr2
Fe+3 and O-2 ….to predict the chemical formula of Fe2O3
4) Special situation: When using subscripts with polyatomic ions (more than one element ions), the formula of the
polyatomic ion is put in parentheses, and the subscript is place outside the parentheses. This applies to compounds
made up of three elements (these are called ternary compounds). (Binary compounds are made up of two elements.)
Ca+2 and NO3-1 …switch ‘em to predict the chemical formula Ca(NO 3)2
Cu+2 and PO4-3 …. To predict the chemical formula Cu3(PO4)2
Naming COVALENT COMPOUNDS ( or MOLECULAR COMPOUNDS)
1. Binary compounds containing two nonmetallic elements are usually molecular.
2. Because each element can have multiple oxidation states, and because the same two elements can form multiple molecular
compounds, latin prefixes must be used: “mono” meaning 1; “di” meaning 2; “tri” meaning 3; “tetra” meaning four;
“penta” 5; “hexa” six, “hepta” 7; “octa” 8; “nona” 9; “deca” 10.
3. The elements with the positive oxidation state (apparent chrg) come first.
The prefixes must be used for both elements except in the case where the first element (the positive chrg) only has one you
can drop the “mono” prefix.
CO2 = carbon dioxide; N2O = dinitrogen monoxide; N2O3 = dinitrogen trioxide;
PCl5 = phosphorus pentachloride
Predicting Formulas of COVALENT COMPOUNDS (aka Molecular Compounds)
are tougher, not too many great rules, just memorization.
In molecular compounds, electrons are shared by two atoms rather than being transferred from one atom to another (like in
ionic compounds). In some molecular cmpnds, the electrons are not shared equally, that is the electrons spend more time near
one atom than the other. The atom having the greater attraction for the electrons is assigned a negative apparent charge (or
oxidation state) while the smaller attraction atom is given a positive apparent charge (or oxidation state).
1) In predicting formulas, the best rule is that the apparent charge of Oxygen in molecular compounds is always –2, that
means it has a greater attraction for two shared electrons (except in the rare case of peroxides like H 202 where the
apparent charge is –1).
2) From here you should be able to calculate the apparent charges of the other elements.
Chemical formula: a notation with chemical symbols and numbers used to 1)
in the elements in a compound and 2) indicate the number of each atom in the
compound
Called molecular formulas when referring to molecular compounds (aka
COVALENT COMPOUNDS); a molecule is one unit of a covalent compound
(for example one C6H12O6 is one molecule of the compound called glucose)
The empirical formula is the simplest whole number ratio of atoms (CH 2O for
the glucose molecular formula mentioned above, by dividing all the atoms by 6)
Called formula units when referring to IONIC COMPOUNDS. This is when a cation
(almost always a metal) gives electrons to the anion (nonmetal). There is a transfer of
electron(s) from one atom to another creating two oppositely charge particles (called a
cation and an anion) which become attracted to one another.
The formula unit for ionic compounds is always the simplest whole number ratio,
therefore it is the same as an empirical formula.
NAMING ACIDS:
In binary acids you start with the prefix hydro- to indicate it is a binary hydrogen compound; then the ending of the
name is modified by the suffix –ic and the word acid is included as part of the name.
In ternary acids, the polyatomic suffix –ate changes to –ic still ending with acid.
And polyatomic suffix –ite changes to –ous still ending with acid.
________-ic acid  for those having a polyatomic ion ending with –ate (sulfate, perchlorate, chlorate)
________-ous acid  for those having a polyatomic ion ending with –ite (nitrite, chlorite, hypochlori
ACID DEFINITIONS:
Acids are a UNIQUE category in that they are covalently bonded nonmetals in the solid salt form, yet dissociate into two
ions when in water (like ionic substances), with the cation always being H+ ions.
Dry (undissolved) acid compounds consist of molecules of neutral charge, yet they are named like ionic
compounds...HSO4(s) is hydrogen sulfate and HNO3(s) is hydrogen nitrate.
Yet when certain compounds are placed in water their molecules interact with water molecules to produce cations (H+
ions) and anions (often halogen ions or polyatomic ions containing oxygen).
Acids are substances that form hydrogen ions H + (or hydronium ions H3O+) in water.
Binary acids are water solutions of binary hydrogen compounds like HCl and H 2S.
Ternary acid is an acid made up of three elements, always hydrogen combined with a polyatomic ion (usually containing
oxygen).
te)
EXAMPLES:
Progression of suffixes use in naming polyatomic anions with oxygen in them. (remember that hypo = “less
than” in Latin and hyper (or per) = “greater than” in Latin)
Prefix/Suffix
Anion Name
Acid Name
perClO4- perchlorate
HClO4 perchloric acid
-ate
ClO3- chlorate(most common)
HClO3 chloric acid
-ite
ClO2- chlorite
HClO2 chlorous acid
hypoClO- hypochlorite
HClO hypochlorous acid
NO3nitrate
HNO3 nitric acid
NO2nitrite
HNO2 nitrous acid
SO4-2 sulfate
H2SO4 sulfuric acid
SO3-2 sulfite
H2 SO3 sulfurous acid
Formula of Compound
HCl
Dry (undissolved) compound
hydrogen chloride
Name of water solution
hydrochloric acid… HCl (aq)
HBr
H2S
hydrogen bromide
hydrogen sulfide
hydrobromic acid…HBr (aq)
hydrosulfuric acid…H2S (aq)