2.4 CHEMICAL FORMULAE AND NOMENCLATURE
(Pages 74-81)
Chemical nomenclature is the system and rules used for naming chemical compounds. The
system has been regulated by the International Union of Pure and Applied Chemistry
(IUPAC).
Synonyms: 1,3,7-trimethyl-2,6-dioxo-1,2,3,6-tetrahydropurine; AlertPep; Caffeine; Cafipel; eldiatric c; Guaranine; Koffein; Mateina; NoDoz; organex; Refresh'n; Stim; Theine;
Oxidation number: The charge assigned to an ion that
indicates the movement of an electron in a compound.
(the bonding capacity or the charge)
Valence electrons: Electrons in the outermost orbits of an element. These are the most
important with respect to the element’s reactivity.
Oxidation number vs. valence electrons
Groups
I
2
13
1
+
2
+
3
1
2
3
Ox. #
+
Val. e-
14
+/-
4
4
15
16
17
-
3
-
2
-
18
1
0
5
6
7
8
IONIC COMPOUNDS
A. BINARY IONIC COMPOUNDS (Metal + Non-Metal)
Chemical Formula  Chemical Name
 Binary compounds are compounds containing two different ions. Ionic compounds
consist of a metal and non-metal.
 The name of the first element is unchanged
 The ending of the second element is changed to ‘ide’
Examples:
KCl
Ca3N2
NaI
Li2S
BeO
Chemical Name Chemical Formula
 To determine the chemical formula, oxidation numbers (charges) are used to find the
number of atoms of each element
 The Zero-Sum Rule (Page 75) takes into consideration that the sum of the positive charges
equals the sum of the negative charges in an ionic compound.
 In the Criss-Cross Rule, simply criss-cross the charges and reduce if necessary
Examples:
Strontium sulfide
Potassium oxide
Barium fluoride
Lithium Hydride
Sodium Nitride
B. BINARY IONIC COMPOUNDS WITH MULTIVALENT ELEMENTS
(Transition Metal + Non-Metal)
 Transition metals can have more than one oxidation state. For example, copper has +1
and +2. Copper (I) and copper (II) when bonded to another anion, can have distinct
physical properties
 If bonded with chlorine, this could result in
CuCl CuCl2 –


Element
Copper
The stock system uses roman numerals in brackets to distinguish valences
The alternate system uses old Latin names to distinguish valences
Ion
Cu+
Cu2+
Iron
Fe2+
Fe3+
Lead
Pb2+
Pb4+
Mercury
Hg22+
Hg2+
Gold
Au1+
Au3+
manganese Mn2+
Mn4+

Stock System
copper (I)
copper (II)
iron (II)
iron (III)
lead (II)
lead (IV)
mercury (I)
mercury (II)
gold (I)
gold (III)
manganese (II)
manganese(IV)
Alternative
cuprous
cupric
ferrous
ferric
plumbous
plumbic
mercurous
mercuric
aurous
auric
manganous
manganic
Element
nickel
chromium
cobalt
tin
palladium
platinum
Ion
Ni2+
Ni3+
Cr2+
Cr3+
Co2+
Co3+
Sn2+
Sn4+
Pd2+
Pd4+
Pt2+
Pt4+
Stock System
nickel (II)
nickel (III)
chromium (II)
chromium (III)
cobalt (II)
cobalt (III)
tin (II)
tin (IV)
palladium (II)
palladium (IV)
platinum (II)
platinum (IV)
Alternative
nickelous
nickelic
chromous
chromic
cobaltous
cobaltic
stannous
Stannic
palladous
palladic
platinous
platinic
When determining the formula, criss-cross the charges as before, except this time use the
charge that corresponds with the roman numeral
Examples:
manganese (II) chloride
tin (IV) fluoride
iron (III) phosphide
cobalt (II) nitride
lead (II) oxide
FeCl2
FeCl3
CuS
SnS2
Pb(SO4)2
C. COMPOUNDS WITH POLYATOMIC IONS
 Compounds that contain one or more polyatomic ions are often called tertiary compounds
or polyatomic ionic compound because they contain three or more elements. These
compounds still contain a cation and an anion.
 Polyatomic ions are ions that contain more than one type of atom, generally oxygen
included.
 Oxyanions are negatively charged polyatomic ions that contain hydrogen
 Acronym: Nick the Camel ate a Clam Supper in Phoenix. These are the most common.
Other important ones are included in your textbook and your study sheet
 When determining the formula, use the charges of the ions and criss-cross
Note: Most polyatomic ions have a negative charge. Ammonium has a positive charge.
Examples:
NH4ClO3
iron (III) hydroxide
Al2(SO4)3
calcium carbonate
Pb(NO3)4
magnesium phosphate
CuOH
copper (I) cyanide
D. POLYATOMIC IONS with VARIABLE OXYGEN
 Some polyatomic ions have a variable number of oxygens. When you add or remove
oxygens, the charges do not change. The base ion is the one with the ‘ate’ ending.
Example:
Parent Polyatomic Ion
‘- ate’
Example: chlorate ClO3-
Add one oxygen
‘per – ate’
Example:
Remove one oxygen
‘- ite’
Example:
Remove two oxygens
‘hypo – ite’ Example:
E. HYDRATES
 Some ionic compounds release water when heated
 A hydrate occurs when water molecules are weakly bonded to the ionic compounds within
its crystal structure
 When the water is present in the ionic compound, the compound is considered hydrated.
When water is removed, the compound is considered anhydrous (without water)
 The first part of the compound is named according to proper nomenclature rules
 The second part represents the number of water molecules (using prefixes)
 A ‘•’ indicates a weak bond between the ionic compound and the water
 Naming: Write the name of the ionic compound followed by prefix + hydrate
Examples:
Na2CO3 • 10H2O
CuSO4 • 5H2O
cobalt (II) chloride hexahydrate
MOLECULAR COMPOUNDS
F.




BINARY COVALENT COMPOUNDS (Non-Metal + Non-Metal)
Covalent compounds consist of two non-metals
Prefixes are used to show the number of atoms of each non-metal
The element closest to the bottom left corner is named first
Prefix + Element Name + Prefix + Element name with ‘ide’ ending

When providing the formula, provide the symbols and subscripts according to the prefixes
and element names.
Examples:
N2O5
sulfur dioxide
BF3
nitrogen trihydride
(no need for mono on first element)
CCl4
carbon monoxide
Exception to the rules:
Do not use a prefix for hydrogen. H2S is hydrogen monosulfide.
G. DIATOMIC MOLECULES
 These are elements that naturally occur in pairs. There are seven.
 Acronym:
I Never Have Clever Brains On Fridays or
I Never Have Clean Briefs On Fridays
Diatomic Molecules
I2
N2
H2
Cl2
Br2
O2
F2
Prefixes
1 – mono
2 – di
3 – tri
4 – tetra
5 – penta
6 - hexa
7 - hepta
8 - octa
9 – nona
10 - deca
ACIDS
H.




(WILL BE SEEN AGAIN IN UNIT 4)
BINARY ACIDS
Acids are compounds that when dissolved in water release hydrogen ions (H+ ions)
Hydrogen is usually the first element in the formula of an acid
Hydrogen can combine with single elements to form binary acids
The name of the acid is in the form ‘hydro – ic acid’
Examples:
Gas compound -->
Acid -->
--> HCl
--> HCl(aq)
Gas compound -->
--> H2S
Acid -->
I.





 H2S(aq)
OXY-ACIDS
Hydrogen combines with a polyatomic ion to form an oxy-acid
All acids with ‘-ate’ endings are called ‘-ic acids’
All acids with one extra oxygen are called ‘per – ic acids’
All acids with one less oxygen are called ‘-ous acids’
All acids with two less oxygen are called ‘hypo – ous acids’
Examples:
HNO3
HNO2
HNO4
HNO
COMMON NAMES
IUPAC NAME
Sodium bicarbonate
FORMULA
NaHCO3
Sodium carbonate
NaCO3
Dinitrogen monoxide
N2O
Dihydrogen monoxide
H2O
Hydrochloric acid
HCl
COMMON NAME
HOMEWORK:
Page 75 PP#1-2, Page 77 PP #1, Page 78 PP#2, Page 79 PP#1, Page 80 #1-2
Page 81 #1-8