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•Binary Compounds: compounds composed of two
elements.
•Binary ionic compounds contain a positive ion (cation)
always written first in the formula and a negative ion
(anion).
•In naming binary ionic compounds, the following rules
apply:
1. The cation is always named first and the anion second.
2. A monatomic (meaning “one-atom”) cation takes its
name from the name of the element. For example,
Na+, is called sodium in the names of compounds
containing this ion.
3. A monatomic anion is named by taking the root of the
element name and adding –ide. Thus the Cl- ion is
called chloride.
•In formulas of ionic compounds, simple ions are
represented by the element symbol: Cl means Cl-, Na
means Na+, and so on.
•The rules for naming binary ionic compounds are
illustrated by the following examples:
Compound
NaCl
KI
CaS
Li3N
CsBr
MgO
Ions Present
Na+, ClK+, ICa2+, S2Li+, N3Cs+, BrMg2+, O2-
Name
Sodium chloride
Potassium iodide
Calcium sulfide
Lithium nitride
Cesium bromide
Magnesium oxide
•Formulas from names: the reverse process is also
important.
•Rules for Writing Formulas of Ionic Compounds
1. The positive ion is given first in the formula.
2. The subscripts in the formula must produce an
electrically neutral formula unit. (Nature does require
electrical neutrality.)
• Formula unit: smallest unit of an ionic compound.
3. The subscripts should be the smallest set of whole
numbers possible.
Example: Write the formulas for the ionic compounds.
1. Barium sulfide
The ions are Ba2+ and S2-. The charges are equal but
opposite, so a 1:1 ratio will give a neutral formula unit.
(2+) + (2-) = 0 (electrical neutrality)
BaS
2. Aluminum chloride
The ions are Al3+ and Cl- (the charge on Cl is 1-; the one
is understood). We can obtain a neutral formula unit by
combining one Al3+ with three Cl-.
1(3+) + 3(1-) = (3+) + (3-) = 0
AlCl3
3. Aluminum oxide
The ions are Al3+ and O2-. In the formula there must be
the same number of positive charges as negative charges
for the compound to be electrically neutral.
This number must be a whole-number multiple of both 3
and 2.
The smallest whole number-multiple of 3 and 2 is 6, so
there must be two Al3+ and three O2- in the formula.
2(3+) + 3(2-) = (6+) + (6-) = 0
Al2O3
•There are many metals that form more than one type of
positive ion and thus form more than one type of ionic
compound with a given anion.
•For example, the compound FeCl2 contains Fe2+ ions, and
the compound FeCl3 contains Fe3+ ions.
•In this case, the charge on the metal ion must be specified
in the name.
•The systematic names for these two iron compounds are
iron(II) chloride and iron(III) chloride, respectively.
•The Roman numeral indicates the charge of the cation.
•Another system for naming these compounds is seen in
older literature and still on some reagent bottles.
•The ion with the higher charge has a name ending in –ic,
and the one with the lower charge has a name ending in
–ous.
•For example, Fe3+ is called the ferric iron, and Fe2+ is called
the ferrous ion.
•The names for FeCl3 and FeCl2 are then ferric chloride and
ferrous chloride, respectively.
•Example: Give the systematic name for each of the
following compounds.
1. CuCl
Because the anion is Cl-, the cation must be Cu+ (for
charge balance), which requires a Roman numeral I.
Copper(I) chloride
2. HgO
Because the anion is O2-, the cation must be Hg2+
[mercury(II)].
Mercury(II) oxide
3. Fe2O3
The three O2- ions carry a total charge of 6-, so the total
positive charge must be 6+ for electrical neutrality.
There are two Fe ions so 6+ divided by 2 = 3+.
The Fe ion is Fe3+ [iron(III)].
Iron(III) oxide
•Example: Given the following systematic names, write the
formula for each compound.
1. Manganese(IV) oxide
The manganese ion has a 4+ charge. There is only one
so the total positive charge is 4+.
Thus, the total negative charge must be 4-.
(4+) + (4-) = 0 (electrical neutrality)
Oxygen ions (oxide) carry a 2- charge; two O2- ions (total
charge 4-) are required by the Mn4+ ion.
MnO2
2. Lead(II) chloride
The lead ion is Pb2+.
Chloride ion has a 1- charge (Cl-).
For electrical neutrality two Cl- ions would be required.
(2+) + (2 x 1-) = (2+) + (2-) = 0
PbCl2
•Example: Name the following using the old nomenclature
system.
1. CrCl3
There are three Cl- ions giving a total 3- charge which
must be balanced by a 3+ charge.
Only one chromium ion is given in the formula so it must
have a 3+ charge.
Remember the ion with the higher charge has a name
ending in –ic and the one with the lower charge has a
name ending in –ous.
Chromium forms the Cr2+ ion and the Cr3+ ion.
Chromic chloride
2. PbS
Sulfide ion has a 2- charge (S2-) so to balance the charges
the lead ion must have a 2+ charge (Pb2+).
Remember lead forms two ions: Pb2+ and Pb4+.
Since we are using the ion with the lower charge it will
have the ending –ous.
Plumbous sulfide
The following flowchart is useful when you are naming
binary ionic compounds.
Does the compound contain
Type I or Type II cations?
Type I: metal present
forms only a single
type of cation.
Type II: metal present
forms more than one
type of cation.
Type I
Name the cation using
the element name.
Type II
Using the principle of charge balance,
determine the cation charge.
Include in the cation name a Roman
numeral indicating the charge.
•Polyatomic ions are assigned special names that must be
memorized to name the compounds containing them.
•Several series of polyatomic anions contain an atom of a
given element and different numbers of oxygen atoms.
These anions are called oxyanions.
•The name of the one with the smaller number of oxygen
atoms ends in –ite and the name of the one with the larger
number ends in –ate.
•For example, sulfite (SO32-) and sulfate (SO42-).
•When more than two oxyanions make up a series, hypo(less than) and per- (more than) are used as prefixes to
name the oxyanions with the fewest and most oxygen
atoms. For example, hypochlorite (ClO-), chlorite (ClO2-),
chlorate (ClO3-), and perchlorate (ClO4-).
•Example: Give the systematic name for the each of the
following compounds.
1. Ca3(PO4)2
Calcium phosphate
2. Na2CO3
Sodium carbonate
3. (NH4)2SO4
Ammonium sulfate
4. Fe(NO3)3
Iron is a transition metal – requires a
Roman numeral. Fe3+ balances three
NO3- ions.
Iron(III) nitrate
•Example: Given the following systematic names, write the
formula for each compound.
1. Calcium sulfate
Calcium forms an ion with a 2+ charge (Ca2+) and the
sulfate ion has a 2- charge (SO42-).
One Ca2+ ion balances charge with one SO42+ ion.
CaSO4
2. Iron(III) acetate
The iron ion has a 3+ charge (Fe3+) and the acetate ion
has a 1- charge (C2H3O2-).
Three acetate ions are needed to balance charge.
Fe(C2H3O2)3
Note: the formula for the acetate is written with
parentheses to show it appears three times.
•Binary covalent compounds are formed between two
nonmetals.
•In the naming of binary covalent compounds, the following
rules apply:
1. The first element in the formula is named first, using the
full element name.
2. The second element is named as if it were an anion.
3. Prefixes are used to denote the numbers of atoms
present.
4. The prefix mono- is never used for naming the first
element. For example, CO is called carbon monoxide,
not monocarbon monoxide.
•Example: Name each of the following compounds.
1. P4S7
Tetraphosphorus heptasulfide
2. I2O5
Diiodine pentoxide
3. S2F10
Disulfur decafluoride
4. OF2
Oxygen difluoride
•Example: From the following systematic names, write the
formula for each compound.
1. Diiodine tetroxide
I2O4
2. Tetraphosphorus triselenide
P4Se3
3. Antimony pentafluoride
SbF5
Flowchart for Naming Binary Compounds
Overall Strategy for Naming Chemical Compounds
•An acid can be viewed as a molecule with one or more H+
ions attached to an anion.
•The rules for naming acids depend on whether the anion
contains oxygen.
•If the anion does not contain oxygen, the acid is named
with the prefix hydro- and the suffix –ic.
•For example, when gaseous HCl is dissolved in water, it
forms hydrochloric acid.
•When the anion contains oxygen, the acidic name is formed
from the root name of the anion with a suffix of –ic or –ous,
depending on the name of the anion.
1. If the anion name ends in –ate, the suffix –ic is added to
the root name.
For example, H2SO4 contains the sulfate anion (SO42-) and
is called sulfuric acid.
2. If the anion has an –ite ending, the –ite is replaced by
–ous.
For example, H2SO3, which contains sulfite (SO32-), is
named sulfurous acid.
Flowchart for Naming Acids.
•Example: name the following acids.
1. HI(g) dissolved in water
The anion does not contain oxygen so the prefix hydroand the suffix –ic is added.
Hydroiodic acid
2. HClO4
The anion contains oxygen and is called perchlorate so
the suffix –ic is added to the name.
Perchloric acid