Chemistry Chapter 7
Ionic Compounds
and Metals
7.1 Ion Formation
 Objectives:
 1.
Define a chemical bond
 2. Describe the formation of
positive and negative ions
 3. Relate ion formation to
electron configuration
Valence Electrons
Definition: valence electrons are electrons
in the highest energy level or outer shell
of an element’s atoms
 To find the number of valence electrons in
an atom of a representative element
(group A), look at its group number
 Definition: a chemical bond is the force
that holds two atoms together
 Definition: electron dot structures are
diagrams that show valence electrons as
dots

Definition: an octet is a set of eight
 Octet rule: In forming compounds,
atoms tend to achieve the electron
configuration of a noble gas
 Each noble gas except for helium has
8 electrons in its outer shell
 Atoms of most metals tend to lose
valence electrons completing an octet
at the next lowest energy level
 Atoms of some metals tend to share
or gain electrons to complete the
octet

Formation of Cations
 Definition:
An ion is an atom or group
of atoms with a charge
 Recall that a cation is an ion with a
positive charge
 An atom’s loss of valence electrons
produces a cation
 Q: How many electrons are in the
highest occupied energy level of Na+?
 A: 8 electrons
 Metal
ions are always cations
 They are reactive because they
lose electrons easily
 Transition metal ions commonly
lose 2 valence electrons
 Transition metal ions can lose 3
or more valence electrons
 Sometimes they lose only one
(ex: Cu+)
 This is due to electron
configuration
 Exceptions
to the rule about
ion formation have to do with
special cases
 Certain metals have more
stable configurations outside
of the octet rule
 You will learn more about the
exceptions later
Formation of Anions
Recall that an anion is an ion with a
negative charge
 The gain of negatively charged
electrons by a neutral atom produces
an anion
 Q: Which noble gas has the same
electron configuration as a chloride
atom?
 A: Argon

Q: Where are the halogens?
 Q: How many electrons do
halogen atoms need to gain the
electron configuration of a noble
gas?
 Nonmetals gain the number of
electrons that equals 8 when
added to their valence electrons
 Some nonmetals like P gain 3 e- or
lose 5 e- to achieve an octet





7.2 Ionic Bonds and Ionic Compounds
Objectives:
1. Describe the formation of ionic
bonds and the structure of ionic
compounds
2. Generalize about the
strength of ionic bonds
based on the physical
properties of ionic
compounds
3. Categorize ionic
bond formation as
exothermic or endothermic
Formation of Ionic Bonds and Ionic
Compounds
 Recall that a compound is a substance
composed of at least 2 elements in a
fixed ratio
 Definition: Ionic compounds are
compounds composed of cations and
anions
 Ionic compounds are electrically neutral
even though they are composed of
cations (+) and anions (-)
In an electrically neutral ionic
compound, the + and – charges equal
each other producing a neutral
compound
 Definition: ionic bonds are the
electrostatic forces that hold ions
together in ionic compounds
 Definition: a chemical formula shows
the kinds and numbers of atoms in
the representative unit of the
substance







Ionic compounds exist as a collection of +
and – charged ions arranged in repeating
patterns
They are a combination of a metal plus a
nonmetal or polyatomics
Definition: a formula unit is the lowest whole
number ratio of ions in an ionic compound
Remember the ionic charges must exactly
cancel each other out
Q: What is the formula unit for sodium
chloride? Magnesium chloride? Aluminum
bromide?
A: NaCl, MgCl2, AlBr3
Properties of Ionic Compounds
1. Most ionic compounds are crystalline
solids at room temperature
 2. Ionic compounds generally have high
melting points
 3. Ionic compounds can conduct electric
current when melted or dissolved in
water
 4. The strong attraction among the
positive ions and negative ions results in
the formation of a crystal lattice

 Definition:
a crystal lattice is a three
dimensional geometric arrangement
of particles
 Each positive ion is surrounded by a
negative ion
 definition: an electrolyte is an ionic
compound whose solution conducts
electricity
 Ionic bonds are relatively strong
 Ionic crystals require a large amount
of energy to break
General Info
 Ions
in an ionic compound are
arranged in a crystal lattice
 Definition: lattice energy is the
energy required to separate
one mol of the ions in an ionic
compound
 Metals are also arranged in
very compact and orderly
patterns
 Metallic
bonding is between
metals only & usually referred
to as a “sea of electrons”
 Definition: an alloy is a mixture
of 2 or more elements, one of
which is a metal
 Ex: brass = copper + zinc
 Alloys often have properties
that are superior to their
component elements
7.3 Names and Formulas for Ionic
Compounds
 Objectives:
 1. Relate a formula unit of an
ionic compound to its
composition
 2. Write formulas of ionic
compounds
 3. Apply naming conventions to
ionic compounds and oxyanions
Take out your periodic table and
write the charges on it as we go
through the groups
 To write chemical formulas for ionic
compounds, you must know the
types of ions that tend to form
 You must know the ionic charges
typically obtained by the elements
 When metals in Groups 1A, 2A & 3A
lose electrons, they form cations
with positive charges equal to their
group number

For monoatomic ions or ions consisting of
only one atom, the ionic charges can
often be determined by using the
periodic table
 The metallic ions in Group 1A (with Na+
and Li+) tend to lose electrons
 Notice that you do not write the number
1 as it is implied by the charge
 These ions have a 1+ charge because
they have 1 valence electron which they
give up to have a complete outer shell
 The group 2A metals (with Ca2+ and Mg2+
form cations with a 2+ charge due to 2
valence electrons

Al is a group 3A metal with a 3+
charge (3 valence electrons)
 The charges on Group A nonmetal
anions are determined by subtracting
the group number from 8
 Nonmetals tend to gain electrons and
form anions, so the sign of the
charge is negative
 Group 7A has a charge of 1- while
Group 6A is 2 Group 5A can form anions with a 3charge or a 5+ depending on
whether it acts as an anion or a
cation

Most of the elements in Group 4A and 0 do
not form ions
 Group 0 or 8A has no charge because its
outer shell has 8 electrons & is full
 Group 4A will share electrons to gain 4
more or it will lose 4 electrons
 The charge for Group 4A can be either 4+
or 4- depending on whether it loses its 4
valence electrons or shares them with
another element
 Whenever an element acts as an anion and
gains electrons (has a negative charge) the
name of the ion will end in -ide and keep
the stem name of the element









Transition metals sometimes have more than
one common ionic charge
The charges for many transition metal cations
is detemined by the number of electrons lost
Fe can exist as Fe2+ or Fe3+
Fe2+ is called iron(II) ion (there is no space
between the Roman numeral and the name)
The older method of naming used the –ous
ending for cations with the lower of the two
ionic charges
The suffix –ic is used to name the cation with
the higher charge
Using this system Fe2+ is called ferrous cation
Fe3+ is called ferric cation







A few of the transition metals have only one
ionic charge
The exceptions are silver (Ag+), with a
cation that nearly always has a 1+ charge,
cadmium and zinc with charges of 2+ (Cd2+,
Zn2+)
Many transition metal compounds are used
as pigments
Ionic compounds will be a combination of a
metal (cation) plus a nonmetal (anion)
When naming these compounds, the cation
comes first & states its full name
The anion trails after and uses its stem
name plus the –ide ending
The exception to this is polyatomic ions
Polyatomic Ions






All the previous ions are monoatomic composed
of only one atom
Definition: the charge of a monoatomic ion is
the oxidation number
Polyatomic ions a combination of more than
one atom that are joined to each other with
covalent bonds
Definition: a nonmetal bonded to one or more
oxygens is called an oxyanion
All polyatomics act as a single unit as if they
are one ion & they carry a charge, making
them participants in ionic bonding
Their presence in a substance indicates an ionic
compound
2 Common Endings
Many polyatomic ions have similar names
 The charges on the ion pairs are the
same, but the ending is different (either
–ite or –ate)
 The -ite ending is used for the partner
which has less oxygen
 The –ate ending is used for the partner
with more oxygen
 The ending, however, does not give the
actual number of oxygens in the
polyatomic ion









For example: The sulfate ion is
composed of one sulfur and four
oxygen atoms (is an oxyanion)
The five atoms together form the
sulfate ion with a 2- charge
Sulfite has 1 sulfur & 3 oxygens with a
2- charge
While most names end in –ite or –ate,
there are exceptions
Important exceptions to that rule are …
The postively charged ammonium
cation (NH4+)
The cyanide ion (CN-) and …
The hydroxide ion (OH-)
When the formula begins with H
(hydrogen), combine the H+ with
another polyatomic ion such as CO32to make hydrogen carbonate, which is
also called bicarbonate
 Hydrogen phosphate (HPO42-) &
dihydrogen phosphate (H2PO4-) are
other examples
 Many such combinations occur
 Many anions and cations are essential
to living systems with the exception of
CN Cyanide stops cells from producing
energy and is lethal to humans

Writing Binary Ionic Compounds
 Definition:
a binary compound is
composed of two elements and
can be either ionic or molecular
 To name any binary ionic
compound, place the cation(+)
name first, followed by the anion
name(-) (which will end in –ide)
 The charges of the cation must
equal the charges of the anion
 The net ionic charge of the
compound must equal zero
 Write
the symbol of the cation
first, followed by the symbol of
the anion
 Add subscripts to balance the
charges
 The ionic compound potassium
chloride is composed of
potassium cations (K+) and
chloride anions (Cl-)
 Write the cation followed by the
anion: KCl, then add subscripts
 Never
write a subscript of 1
 One is always implied: only add
subscripts if a number other
than one is needed
 In the case of KCl, the
potassium carries a charge of
1+ and the chloride has a
charge of 1 These 2 numbers add up to
zero, so the formula is balanced
 Calcium
bromide will require
subscripts
 Calcium ion has a charge of 2+
while bromide has a charge of 1 You need 2 bromides to make the
charges add up to zero
 It looks like this: CaBr2
 The calcium is 2+, bromide is now
2 x -1 or 2 -2 + 2= 0, so it is balanced
 Some
formulas are more
complicated such as rust
 Fe3+ ions combine with oxide
anions (O2-)
 One method of writing the
balanced formula requires finding
the least common multiple of the
charges
 The result is Fe2O3
 Q: Write the formula for calcium
sulfide
Naming Binary Ionic Compounds
When naming binary ionic compounds it
is helpful to know the charges of the
transition metals
 Tin (Sn) forms cations with 2+ and 4+
charges
 One compound is tin(IV) oxide (SnO2)
because only the tin(IV) cation can
balance the two oxide anions with their
2- charges
 Q: What is the name of the compound
that has the formula SnO?
 A: tin(II) oxide or stannous oxide

Compounds with Polyatomics
In order to balance and name these
compounds, you must recognize them!!
 Compounds with polyatomics will have
at least 3 elements that make up the
compound
 Write the symbol for the cation followed
by the formula for the polyatomic ion
and then balance the charges with
subscripts
 If the cation is a polyatomic, write it first
followed by the element or polyatomic
that follows

 Ex:
calcium nitrate→Ca(NO3)2
 The calcium has a charge of 2+
and the nitrate is 1 Parentheses are used around the
nitrate ion because more than 1
nitrate ion is needed
 When more than one polyatomic
ion is needed to balance a formula,
parentheses in the formula set off
the polyatomic ion
 This is the only time parentheses
are used
Ex: K2Cr2O7 consists of two
potassium ions combined with one
chromate polyatomic ion
 It is called potassium dichromate
 Q: What is the formula for
ammonium carbonate?
 Q: When are parentheses used in
formula writing?
 Q: What is the formula for
magnesium hydrogen carbonate?
 Q: What is another acceptable
name for magnesium hydrogen
carbonate?

Problem Solving Strategy page
224- Naming Ionic Compounds
1. Determine the cation and the anion
of the given formula
 2. Does the cation have only one
oxidation number?
 A. if yes, write the name of the cation
followed by the name of the anion
 B. if no, write the name of the cation
followed by a Roman numeral to
represent the charge followed the
name of the anion

Naming
Writing Formulas




In writing a formula from a name,
remember these rules:
1. in an ionic compound the net charge is
zero
2. an –ide ending generally indicates a
binary compound
3. an –ite or –ate ending means there is a
polyatomic ion that includes oxygen in the
formula
4. Prefixes in a name generally indicate
that the compound is molecular
 5. A Roman numeral after the name of a
cation shows the ionic charge of the cation
 Q: Tell whether the following is correct or
incorrect. If it is incorrect, tell why.
 A. magnesium(II) chloride
 B. boron oxide
 C. Na2C2O4
 D. Ca(NH4)2
