CHEMICAL FORMULAS AND
CHEMICAL COMPOUNDS
Objectives:
1. Explain the significance of a chemical
2.
3.
4.
5.
formula.
Determine the formula of an ionic
compound formed between two given ions.
Name an ionic compound given its formula.
Using prefixes, name a binary molecular
compound from its formula.
Write the formula of a binary molecular
compound given its name.
Chemical names and Formulas
 There are millions of natural and synthetic
chemical compounds
 Calcium carbonate – limestone
 Sodium chloride – table salt
 Dihydrogen monoxide – water
 These are their chemical and common names
 Chemical names help to describe the atomic makeup
of the compounds
Significance of a Chemical
Formula
 Chemical formula
 Indicates the relative number of atoms of each
kind in a chemical compound.
 Molecular formula
 Indicates the relative number of atoms of each
kind in a molecule. (Covalently bonded)
C8H18
Subscript indicates there
are 8 atoms of carbon in a
molecule of octane
Subscript indicates there
are 18 atoms of hydrogen
in a molecule of octane
 Chemical formula for ionic compound
 Ionic compound consists of lattice of positive and
negative ions held together by mutual attraction.
 Chemical formula represented by one formula unit
 Simplest ratio of the compounds positive and negative
ions
 Aluminum sulfate below consists of aluminum cations
and sulfate ions
Al2(SO4)3
Subscript 2 refers to 2
Aluminum atoms
Note: when you only
have one of an atom,
no subscript is used
Subscript 4 refers
to 4 oxygen atoms
in the sulfate ion
Subscript 3 refers to
everything inside the
parentheses giving 3
sulfate ions, with a total
of 3 sulfur atoms and 12
oxygen atoms
Note: parentheses are
used to identify
polyatomic ion as one unit
Monatomic ions
 Ions formed from a single atom
 Examples
 Na+1
 Mg2+
 S2 N-3
 Cl1-
lose one electron
gain two electrons
 Not all main-group elements readily form ions
 Examples
 Carbon & Silicon form covalent bonds
 d-block elements form variable charges
 examples
 Copper, can be Cu+1 or Cu+2
 Iron, can be Fe+2 or Fe+3
 Lead, can bePb+2, Pb+3, or Pb+4
Naming Monatomic ions
 Positive ions
 Name of element
 Ex: K+
Potassium
Mg+2
Al+3
Sr+2
Magnesium
__________
__________
 Negative ions
 Base of element + -ide ending
 Ex: F-1
Fluoride
N-3
O-2
Br-1
Nitride
_______
_______
Binary Ionic Compounds
 Compounds composed of two different
elements
 Total # of positive charges must be equal to total # of
negative charges
 Writing formulas, Ex: Aluminum oxide
1.
Write the symbols for ions (Cation first)
Al+3 O-2
2.
Cross over the charges as subscripts
+3
-2
Al2O3
3.
Check to make sure total charges are equal, divide by largest
number, to give smallest whole-number ratio
Al2O3
2 x (+3) = +6
3 x (-2) = -6
Naming binary ionic
compounds
 Nomenclature
 Naming system
 Name Al2O3
 Name cation first : full name of cation
 Aluminum
 Name Anion last : base of anion + -ide
 oxide
Al2O3
aluminum oxide
Practice Naming and Writing
Formulas
 Name
AgCl
2. ZnO
3. SrF2
1.
silver chloride
zinc oxide
strontium fluoride
 Write the formulas for
Zinc iodide
ZnI2
ZnS
2. Zinc sulfide
3. Aluminum sulfide
1.
Al2S3
Stock System of Nomenclature
 Some cations may have two or more different charges
 Use stock system of naming (usually with d-block elements)
 Roman numeral represents charge in parentheses
 Fe+2
Iron(II)
Fe+3
Iron(III)
 Some cations that commonly form only one cation
 Do not use roman numerals ( main group elements)
 No Anions form more than one charge
+2 -1
CuCl2
copper(II) chloride
Practice stock system
 Write formula and give name for compound
formed by ions Cr+3 and F-1
CrF3
chromium(III) fluoride
 Write formulas and give name for the
following ionic compounds:
Cu+2 and Br-1
CuBr2
copper(II) bromide
Fe+2 and O-2
FeO
iron(II) oxide
Fe+3 and O-2
Fe2O3
iron(III) oxide
Compounds containing
Polyatomic Ions
 All but NH4+, ammonium ion, are negatively
charged
 Most are oxyanions
 Examples
 NO3-1
nitrate
NO2-1
nitrite
 Most common anion has –ate ending
 Anion with one less oxygen has –ite ending
 Anion with two less oxygen has hypo prefix and –ite
ending
 Anion with one extra oxygen has per prefix and –ate
ending
ClO3-1
chlorate
ClO2-1
chlorite
ClO-1
hypochlorite
ClO4-1
perchlorate
Naming Compounds with
Polyatomic Ions
 Same as naming for ionic compounds except
 Name polyatomic ion as one unit
 Example:
 AgNO3
silver nitrate
 Use parentheses if more than one polyatomic ion
 Example
 Al2(SO4)3
aluminum sulfate
Show 2 Al+3 ions and 3 SO4-2 ions
Writing Formulas and Naming
Compounds with Polyatomic Ions
 Write the formula for these:
1.
2.
3.
4.
5.
tin(IV) sulfate
Sn(SO4)2
calcium chloride CaCl2
lithium nitrate
LiNO3
calcium nitrite
Ca(NO2)2
potassium perchlorate
KClO4
 Write the names for these:
1.
2.
3.
4.
5.
Ag2O
Ca(OH)2
NH4OH
FeCrO4
KClO
silver oxide
calcium hydroxide
ammonium hydroxide
iron(II) chromate
potassium hypochlorite
Naming Binary Molecular
Compounds
 May use stock system to name these
 New system – must understand oxidation
numbers
 Prefix system
 Old system – must know numerical prefixes
1. mono-
6. hexa-
2. di-
7. hepta-
3. tri-
8. octa-
4. tetra-
9. nona-
5. penta-
10. deca-
Rules for prefix system of
Nomenclature
1. less-electronegative element is given first
• First element only gets a
prefix if it has more than one
Ex:
P4O10
2. Second element is named by combining
a. Prefix indicating number of atoms
b. Root of name of second element
c. -ide ending
Ex:
tetra phosphorus decoxide
3. The o or a at the end of a prefix is usually
dropped when the word following the prefix
begins with another vowel
The 6 binary compounds of
Nitrogen and Oxygen
N2O
NO
NO2
N2O3
N2O4
N2O5
dinitrogen monoxide
nitrogen monoxide
nitrogen dioxide
dinitrogen trioxide
dinitrogen tetroxide
dinitrogen pentoxide
•Name the following
molecular compounds
•Write formulas for the following
molecular compounds
1. SO3 sulfur trioxide
1. carbon tetraiodide
CI4
2. ICl3 iodine trichloride
2. phosphorus trichloride PCl3
3. PBr5 Phosphorus pentabromide 3. oxygen difluoride
OF2