JOURNAL 24
 Why
is it important for chemist to
know chemical names and formulas?
 What
is the difference between an
Ionic and Covalent bond?
TODAY WE WILL DETERMINE THE
FORMULA OF AN IONIC COMPOUND
FORMED BETWEEN TWO GIVEN IONS
SIGNIFICANCE OF A CHEMICAL
FORMULA
Chemical formula- indicates the relative number
of atoms of each kind of chemical compounds.
 Example



C8H18
Subscriptindicates that there are 8 carbon atoms in a molecule
of octane
 Indicates that there are 19 hydrogen atoms in a
molecule of octane


Unlike a molecular compound, an ionic compound
consists of lattice of positive and negative ions
held together by mutual attraction.
A CHEMICAL FORMULA
Al2(SO4)3
 Note
how the parenthesis is used.
 They surround the polyatomic anion to
identify it as a unit.
 The subscript 3 refers to the entire unit.
 When there is no subscript next to an
atom’s symbol, the value of the subscript
is one.
MONATOMIC IONS
Ions formed from a single atoms are known as
monatomic ions.
 By gaining or losing electrons, many elements form ions
with noble-gas configurations.
 Examples
 Group 1 metals lose one electron to give 1+ cations
 Na+
 Group 2 metals lose two electrons to give 2+ cations
 Mg 2+
 Nonmetals of groups 15-17 gain electrons
 N3 S2
NAMING MONATOMIC IONS
 Monatomic
cations are identified by the
elements name
 Monatomic anions
 Ending of the name is dropped
 -ide is added to the root name
Examples: chloride, sulfide, fluoride
 Elements with multiple ions
 Examples:
Iron (II), Iron (III),
 Cobalt (II), Cobalt (III)
 Copper (I) Copper (II)

BINARY IONIC COMPOUNDS
 Binary
compounds- compounds composed
of 2 elements
 The total number of positive charges must
equal the number of negative charges
 Examples: Mg and Br,
 As an aid to determining subscripts in
formulas for ionic compounds, the positive
and negative charges can cross – over.
 Example: Al (3+) and O (2-)  Al2O3
NAMING BINARY IONIC COMPOUNDS
The name of the cation is given first followed by
the anion.
 Examples
 Al2O3  Aluminum Oxide


CaBr2

BaO
YOUR TURN TO PRACTICE
CAN YOU WRITE THE FORMULA WHEN
GIVEN THE NAME?
Barium oxide
 Potassium chloride
 Strontium bromide
 Lithium sulfide

YOUR TURN TO PRACTICE
STOCK SYSTEM OF NOMENCLATURE
 Some
elements have 2 or more cations
(with different charges)
 Examples: Iron, Copper
 Use Roman numeral to indicate the ion’s
charge
 The numeral is in parentheses and placed
right after the metal name
 Fe2+ - Iron (II)
 Metals that form only one cation do not
include a roman numeral
PRACTICE
 Write
the formula and give the name for
the compound formed by the ions Cr3+ and
FWrite the symbols for the ions side by side
(cation first)
 Cross over charges to give subscripts

Answer: Chromium (III) Flouride; the formula
is CrF3
PRACTICE
 Write
the formula and give the name for
the compound formed by the ions Cu2+ and
BrWrite the symbols for the ions side by side
(cation first)
 Cross over charges to give subscripts

Answer: Copper (II) Bromide; CuBr2
PRACTICE
 Write
the formula and give the name for
the compound formed by the ions Fe2+ and
O2Write the symbols for the ions side by side
(cation first)
 Cross over charges to give subscripts

Answer: Iron (II) oxide; FeO
PRACTICE
 Write
the formula and give the name for
the compound formed by the ions Pb2+ and
ClWrite the symbols for the ions side by side
(cation first)
 Cross over charges to give subscripts

Answer: Lead (II) chloride; PbCl2
PRACTICE
 Write
the formula and give the name for
the compound formed by the ions Hg2+ and
S2Write the symbols for the ions side by side
(cation first)
 Cross over charges to give subscripts

Answer: Mercury (II) sulfide; HgS
PRACTICE
 Write
the formula and give the name for
the compound formed by the ions Sn2+ and
FWrite the symbols for the ions side by side
(cation first)
 Cross over charges to give subscripts

Answer: Tin (II) fluoride; SnF2
PRACTICE
 Write
the formula and give the name for
the compound formed by the ions Fe3+ and
O2Write the symbols for the ions side by side
(cation first)
 Cross over charges to give subscripts

Answer: Iron (III) oxide; Fe2O3