IONS
Objectives
Determine the number of valence
electrons in an atom of a representative
element
 Explain how the octet rule applies to
atoms of metallic and nonmetallic
elements
 Describe how cations form
 Explain how anions form

Key Vocabulary
 Octet
rule
 Ion
 Cations
 Anions
 Halide
ions
Octet Rule
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In 1916, chemist Gilbert Lewis used the fact
that noble gases are unreactive in chemical
reactions to explain why atoms form certain
kinds of ions and molecules
He called his explanation the octet rule
An octet is a set of 8 and each noble gas,
except for helium, has 8 electrons in the
highest energy level and a general electron
configuration of ns2np6
The Octet Rule
 When
atoms form
compounds, they tend to
achieve the electron
configuration of a noble gas
Octet Rule Applied
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Atoms of the metallic elements tend to lose
their valence electrons leaving a complete
octet in the next lowest energy level
Atoms of nonmetallic elements tend to gain
electrons or to share electrons with another
nonmetallic element to achieve a complete
octet
Most elements follow the octet rule, but there
are some exceptions
Ion Formation

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Ion is an atom that has lost or gained a valence
electron, resulting in a positive or negative
charge
Cation is a positively charged ion
Anion is a negatively charged ion
Both have an electron configuration like a noble
gas
Formation of Cations
A cation forms when an atom loses 1 or
more valence electrons
 For metallic elements the name of the
cation is the same as the element

For example, a sodium atom forms a sodium
cation Na+
 Calcium forms a calcium cation Ca2+

Formation of Cations
Cont.
Although the name is the same, there are
chemical differences between an
between metals and their cations
 For example: Sodium metal reacts
explosively with water however sodium
cations are quite unreactive
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This is why table salt doesn’t explode in your
mouth
Producers of Cations
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The most common cations of the periodic
table are produced by metal atoms
Most metal atoms have 1 to 3 valence
electrons that can be easily removed
We can represent the electron loss or ionization
by drawing the complete electron configuration
of the atom and of the ion formed
Representing Ionization
Both the sodium ion and the neon atom
have 8 electrons in their valence shells
 So it is easier to represent the process
using electron dot structures
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Ionization Practice

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Write an ionization equation for the
calcium ion.
Write an ionization equation for the
potassium ion.
Characteristics of Stable
Cations
The name for the cation of a neutral atom
is the same as the neutral atom
 Both the atom and the ion have the same
number of protons and neutrons
 An atom and its ion have different
chemical properties
 Ions have an electrical charge, they form
compounds, and conduct electricity when
dissolved in water

Stable Ions Cont.
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Many stable ions have noble-gas configurations
Some stable ions do not have noble-gas
configuration
For example:
 Transition metals often form ions without
complete octets
 They are also all cations
Exceptions to the Rules
Ions with charges higher than 3 are rare
 So, some element have to form pseudo
noble-gas configurations
 Silver, copper, gold, cadmium and
mercury are elements with a pseudo
noble-gas configuration

Pseudo Noble-Gas
Configuration
Formation of Anions
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An anion is a negatively charged ion that is
formed by the gaining of electrons
The name of anion of a nonmetallic element is
not the same as the element name
The name of the anion typically ends in –ide
For example:
 the chlorine atom becomes the chloride ion
 The oxygen atom becomes the oxide ion
Representing Ionization

The elements that form anions have
relatively full valence shells, so it is easier
for them to attain noble-gas
configurations by gaining electrons
Halide Ions
Ions that are produced when atoms of
halogens gain electrons are called halide
ions
 All halogen atoms have 7 valence electrons
and only need 1 electron to achieve a
noble gas configuration
 All halide ions have a charge of 1
Ionization Practice

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Write an ionization equation for the
fluoride ion.
Write an ionization equation for the
oxide ion.