Chemical formula - combination of
symbols that represent the
composition of a compound
 Shows
elements present and
number of atoms
subscripts
 Represent
the number of atoms of
that element in the compound
 No
subscript is an “understood” 1
NaCl
 1 Na
1 Cl
 H2SO4
2H 1S 4O
 Ca(ClO3)2
?????
 1 Ca
2 Cl
6O

Two types of compounds we will
learn how to write formulas for
Ionic – transfer of electrons
Covalent – share electrons
(called Molecular)
Molecular Compounds
(covalent)
unit – “molecule”
(bonded covalently)
 Representative
of elements – nonmetals
 Physical state – solid, liquid, gas
Solids – low melting point,
brittle
 Type
– electrically neutral
group of atoms that act as a
unit
Molecule
Naming binary molecular
compounds
2
elements in the compound
 Both nonmetals!
 2 naming systems
 Prefix system
 Stock system (roman numerals)
 Both systems are correct
 I’m sure you will prefer the prefix
system!
PREFIXES YOU MUST MEMORIZE!
Number of
atoms
1
2
3
4
5
6
7
8
9
10
Prefix used
mono
di
tri
tetra
penta
hexa
hepta
octa
nona
deca
 When
2 nonmetallic elements
combine
 Often do so in more than one
way
 Example
CO
CO2
 Problem with calling them both
“carbon oxide”

CO2 – you exhale. It is normally present in
the air you breathe

CO – hopefully is not in the air you breathe
In large amount R.I.P.
Catalytic converter – cars


 Converts CO to CO2

Prefix + first element name
Followed by prefix + 2nd element name with
“ide” ending

******only time

you can not use
a prefix is if the first element in the
compound is a single atom
PCl3
phosphorus trichloride



CO
Carbon monoxide (not monocarbon
monoxide!)

Don’t use “double vowels”
Change if a “tongue twister”
Monooxide  monoxide
Decaoxide  decoxide

Trioxide – is fine









N2O
Dinitrogen monoxide
SF6
Sulfur hexafluoride
N2H4
Dinitrogen tetrahydride
 NO FACTORING ALLOWED!!!
P2O3
Diphosphorus
trioxide
Name the following:
• CS2
• Carbon disulfide
• Cl2O7
• Dichlorine heptoxide
• P4O10
• Tetraphosphorus decoxide
• N2O5
• Dinitrogen pentoxide
• CCl4
• Carbon tetrachloride
Write formulas for the following:
•carbon tetrabromide
•CBr4
•dinitrogen tetrahydride
•N2H4
• boron trichloride
• BCl3
• diphosphorus trioxide
• P2O3
•A molecular
compounds
worksheet just for
you!!
IONIC COMPOUNDS
• Four different types we will learn
about
• Metal + nonmetal (binary ionic)
• Metal + polyatomic ion
• Polyatomic ion + polyatomic ion
• Polyatomic ion + nonmetal
Ionic Charges
• Monatomic ions – ions consisting of only
one atom
• Charges can often be determined by using
the periodic table
• Metallic elements – tend to lose electrons
to form cations
• Group 1 – all 1+
• Group 2 – all 2+
Nonmetals
• Nonmetals tend to gain
electrons when they bond
with metals – form anions
Transition metals
• Many have more than one
common ionic charge
Are going to use roman
numerals
I, II, III, IV, V
Oxidation number
• Indication of how many electrons it will
gain or lose when it forms a bond
• Gains or loses electrons – forms an ion
• Charged particle
• Can be found for each element on the
periodic table
• Refer to yours!!!
 Some elements have more
than 1 oxidation number –
that means they can form
more than one type of
compound
When a single atom takes on a charge
(by gaining or losing electrons) – it
forms a
“monatomic ion”
 Ion made up of more than 1 atom –
“polyatomic” ion

• Monatomic ions
• Na+ Ca+2
Cl-
O-2
• Polyatomic ions
• CO3-2
ClO3-
OH-
 Why would an atom want to
form an ion?
 Remember the “octet rule”
 Wants a filled outer shell
 For most atoms, that is 8
 Samples on board using
electron dot notation
 Na and Cl
 Ca and Cl
 Al and Cl
 Ca and S
 K and N you do
Metal always written first – has
positive oxidation number (written
first)
 Nonmetal written second – has
negative oxidation number

 Can use “criss-cross” method to
arrive at correct formula.
 Must remember to factor
subscripts if possible!!
 Magnesium oxide - MgO






Metal full name first
Nonmetal name with “ide” ending
NaCl
sodium chloride
CaCl2
calcium chloride
LiF
lithium fluoride
AlBr3
aluminum bromide




Use Roman numerals to specify the oxidation
number used
I, II, III, IV, V, VI, VII, VIII
Transition metals characteristically have
multiple oxidation numbers
ONLY USE ROMAN NUMERALS IF THE
METAL HAS MORE THAN ONE OXIDATION
NUMBER LISTED
 Nonmetals may have more than
one oxidation number, you just
use the first number listed NEGATIVE

Co, Ni, Cu, Fe, Mn

Always check before writing name for the
compound
FeCl2
Iron(II) chloride
FeO
Fe2O3




 calcium sulfide
 CaS
 strontium bromide
 SrBr2
 chromium(III) chloride
 CrCl3
 iron(II) oxide
 FeO
 Fe2O3
 Iron(III) oxide
 KI
 Potassium iodide
 CuO
 Copper(II) oxide
 NiCl3
 Nickel(III) chloride
 CrO3
 Chromium(VI) oxide
2. Metal + polyatomic ion
 Almost
all polyatomic ions have a
negative charge
 2 you are responsible for have a
positive charge NH4+ and H3O+
 Polyatomic ions travel as a unit
 Page
102 in text - list of polyatomic ions
 You will use the table I gave you
NEVER
CHANGE
THE SUBSCRIPTS IN
A POLYATOMIC ION
THAT MEANS
NEVER!!!!!!!


Can use same “criss-cross” method for
determining the correct formula
Same rules apply – must factor the subscripts
if you can (only the oxidation numbers that
are used – NOT THE SUBSCRIPTS OF THE
POLYATOMIC ION!!!!!!


At first, always put a parenthesis around the
polyatomic ion
Only time the parenthesis can be dropped is if
a “1” criss-crosses down or if the subscript
factors to a “1”

Don’t forget to include a roman numeral in
the name if the metal has multiple oxidation
numbers!!!!!!
Metal name first (only use roman
numeral if the metal has more than
one oxidation number!!!)
 Second is the name of the polyatomic
ion – taken directly from the table!!

Don’t make up
your own
name!!!!!!!!
Representative unit = “formula unit”
Type of elements: Metal with
nonmetal
 Physical state: crystalline solid (hard)
 High melting point
 Most are soluble in H2O


 Poor conductors of electricity in
the solid state
 But good conductors when
melted (molten) or dissolved in
H2O (aq) (ions free to move)





Oxyacids – contain H, O and a third
element (usually a nonmetal)
Acetic
HCH3COO (acetate ion)
Nitric
HNO3
(nitrate ion)
Nitrous
HNO2
(nitrite ion)
Phosphoric H3PO4
(phosphate ion)







Sulfuric
H2SO4
Sulfurous
H2SO3
Carbonic
H2CO3
Hypochlorous HClO
Chlorous
HClO2
Chloric
HClO3
Perchloric HClO4
(sulfate ion)
(sulfite ion)
(carbonate ion)
(hypochlorite ion)
(chlorite ion)
(chlorate ion)
(perchlorate ion)
 HF
 HCl
 HBr
 HI
hydrofluoric acid
hydrochloric acid
hydrobromic acid
hydroiodic acid