REVIEW OF CHEMICAL FORMULAS AND NOMENCLATURE
Ionic Compounds
Writing Chemical Formulas
Binary ionic compounds
1. Use the Criss-Cross rule to find the subscripts on each of the elements:
Criss-cross the charge on each ion, to find the subscript on the opposite ion.
This is a shortcut rule that will determine the number of atoms required to achieve an electrically-neutral
combination of cations and anions.
Example:
Aluminum + Oxygen
3+
Al
Al forms a 3+ cation; Oxygen forms a 2- anion
2-
2 Al3+ ions will combine with 3 O2- ions
O
Al2O3
The formula of aluminum oxide is Al2O3.
2. If the subscripts have a common factor, reduce to lowest terms.
Example: Beryllium + Sulfur
Be forms a 2+ cation; Sulfur forms a 2- anion
2+
Be
2-
S
Be2S2
reduce
the formula of beryllium sulfide is BeS.
 Practice: Write formulas for the following compounds:
(a) lithium chloride
_________
(f) barium bromide
_________
(b) beryllium chloride
_________
(g) francium phosphide _________
(c) arsenic (V) sulfide
_________
(h) gallium sulfide
_________
(d) calcium carbide
_________
(i) silver nitride
_________
(e) cobalt (III) phosphide
_________
(j) titanium (IV) carbide _________
Polyatomic ionic compounds
3. If there is a subscript on a polyatomic ion, write brackets around the ion, and write the subscript
outside the brackets. If the subscript is one, do not write brackets.
Example:
Calcium + Hydroxide
2+
Ca
Ca forms a 2+ cation; Hydroxide is a 1- anion
1-
1 Ca2+ ions will combine with 2 OH- anions
OH
Ca(OH)2
Example:
The formula of calcium hydroxide is Ca(OH)2.
Aluminum + Phosphate
3+
Al
3-
PO4
Al3(PO4)3
reduce
AlPO4
 Practice: Write formulas for the following compounds:
(a) manganese (IV) hydroxide_________ (g) cesium bromate
_________
(b) lithium sulphate
_________
(h) barium chlorate
(c) ammonium carbonate
_________
(i) potassium phosphate_________
(d) antimony (III) nitrate
_________
(j) nickel (III) carbonate _________
(e) iron (II) phosphate
_________
(k) ammonium phosphate_________
(f) barium manganate
_________
(l) beryllium acetate
Naming Ionic Compounds
BaCl2
Li3N
2+
Fe
barium chlorine chloride
lithium nitrogen nitride
3. If the metal is a multivalent metal (has more than one possible cation
charge), write the charge in Roman numerals and brackets
immediately after the metal name.
Examples:
FeCl2
FeCl3
PbO2
iron (II) chloride
iron (III) chloride
lead (IV) oxide
 Practice: Name the following compounds:
(a) LiF
___________________________
__________
Determining the cationic charge:
To find the charge of the metal,
reverse the criss-cross rule.
Binary Compounds
1. Name the metal element first, then the non-metal.
2. Change the ending of the non-metal to “ide”.
Examples:
_________
1-
Cl 2
The charge on the iron cation is 2+.
[ 2+
1- ] × 2
Pb O 2
The charge on the lead cation is 4+.
(since the charge on the oxide ion is always 2- and
never 1-, the subscripts must have been reduced)
(f) CsI ___________________________
(b) Au2O3 ___________________________
(g) TiO2__________________________
(c) AlP
___________________________
(h) SrAt2___________________________
(d) FeCl3
___________________________
(i) Al4C3___________________________
(e) MnS2
___________________________
(j) Cu3P2__________________________
Polyatomic Compounds
4. Name the cation, then name the anion.
Examples:
NaNO3
(NH4)3N
Fe2(SO4)3
sodium nitrate
ammonium nitride
lead (II) sulfate
(a) LiOH ___________________________
(g) (NH4)2S__________________________
(b) K2CO3 ___________________________
(h) Ti(CO3)2_________________________
(c) Sn(ClO3)4___________________________
(i) Al2(SO4)3_________________________
(d) GaPO4 ___________________________
(j) Ni(OH)2__________________________
(e) FeSO4 ___________________________
(k) Hg3PO4___________________________
(f) Ba(CN)2___________________________
(l) Cu(IO3)3___________________________
Extension: Polyatomic ions
There are four polyatomic ions that contain chlorine and oxygen. They all have the same charge, but
different numbers of oxygen atoms:
ClO2-
ClO-
ClO3-
ClO4-
ClO3- is the chlorate ion; this is the most common combination of chlorine and oxygen. It is known as the
parent ion (and recognized by its “-ate” ending). Some other elements can also form multiple oxyanions;
their names can be derived from the name of the parent anion.
Number of O atoms
x+1
x
x-1
x-2
Rules for naming oxyanions
Naming rule
Example
per_______ate
perchlorate
ClO4_______ate
chlorate
ClO3_______ite
chlorite
ClO2hypo_______ite
hypochlorite
ClO-
Practice: Identify the parent ion, then name the oxyanion.
Oxyanion
Parent ion
Oxyanion name
22(a) CO2
carbonate, CO3
carbonite
3(b) PO2
(c) CrO32(d) SO32(e) CO42-
Molecular Compounds
Naming Binary Molecular Compounds
1. Name elements that are present. Change ending of second one to “ide”.
2. Add prefixes to indicate the number of atoms of each element*
Prefixes for Molecular Compounds
Number of atoms
Prefix
Number of atoms
1
hex
6
2
hept
7
3
oct
8
4
non
9
5
dec
10
Prefix
mono
di
tri
tetra
pent
*
Example
P2O5
2 × Phosphorus; 5 × Oxygen
Examples:
CO2
CO
carbon dioxide
carbon monoxide
exception: Don’t write “mono” on the first element
phosphorus and oxygen are present
____ phosphorus ____oxide
diphosphorus pentoxide
 Practice: Name the following compounds:
(a) H2O
________________________
(b) NH3
________________________
(c) PCl5 ________________________
(d) BI3
________________________
(e) N2H5 ________________________
(f) SO3
________________________
(g) N2O
________________________
Writing Formulas for Binary Molecular Compounds
1. Write the symbols of the elements
2. Interpret the prefixes and write the appropriate subscript
Example
Nitrogen trioxide
1 × Nitrogen; 3 × Oxygen
Nitrogen and oxygen present
N_ O _
NO3
 Practice: Write formulas for the following:
(a)
nitrogen trifluoride
________
(b)
nitrogen monoxide
________
(c)
diboron trioxide
________
(d)
phosphorus trichloride
________
(e)
dinitrogen tetroxide
________
(f)
sulfur hexafluoride
________
(g)
xenon triiodide
________
Element
hydrogen
Diatomic elements
Some non-metals exist as diatomic molecules in their elemental form (two of the same
atom bonded together): HOFBrINCl
oxygen
fluorine
bromine
iodine
Acids
nitrogen
+
Acids are substances that dissolve in water to produce H ions.
In order to display its acidic properties, it must be in the aqueous state (aq).
The formulas of acids always begin with H.
Naming and writing formulas for acids
Binary acids (H + element, aq)
1. Identify the element bonded to H, and write its name.
2. Write “hydro-” in front of the element, and change the ending to “-ic acid”
Example
HF (aq)
Fluorine is bonded to hydrogen
The name of this acid is hydrofluoric acid.
H2S (aq)
hydrosulfuric acid
chlorine
Molecule
H2
O2
Oxyacids (H + polyatomic anion, aq)
1. Identify the element (other than oxygen) in the oxyanion, and write its name.
2. Change the ending to “-ic acid” if the anion ends in –ate, or “-ous acid” if anion ends in –ite. (See
table below)
Name of oxyanion
per_______ate
_______ate
_______ite
hypo_______ite
Example
Name of acid
Example
Anion
perchlorate, ClO4chlorate, ClO3chlorite, ClO2hypochlorite, ClO-
per_________ic acid
_________ic acid
_________ous acid
hypo_________ous acid
Acid
perchloric acid
chloric acid
chlorous acid
hypochlorous acid
The bromate ion (BrO3-) is bonded to hydrogen
The name of this acid is bromic acid.
HBrO3 (aq)
 Practice: Identify the anion, and name/write the formula for the following acids:
Acid formula
(a) H2S (aq)
Anion
S2-
Acid name
(b) HF (aq)
(c) HNO3 (aq)
(d) HI (aq)
(e) HIO3 (aq)
(f) H2SO4 (aq)
(g) HBr (aq)
(h) H3PO2 (aq)
(i) H3P (aq)
(j)
phosphoric acid
(k)
nitrous acid
(l)
bromic acid
(m)
chloric acid
(n)
hyposulfurous acid
(o)
hydrofluoric acid
(p)
carbonic acid
(q)
sulfuric acid
(r)
hypochlorous acid
HClO4
HClO3
HClO2
HClO