Chapter 18 –
Chemical Bonds
Ionic Bonding
Vocabulary
 electron
dot diagram
(Lewis dot structure, LDS)
 ion
 anion
 cation
 chemical bond
 ionic bond
 chemical formula
 crystals
Recognize stable electron
configurations
 Keep
in mind that we are only dealing with the
representative elements.
 When the highest occupied energy level of an
atom is filled with electrons, the atom is stable
and not likely to react.
 The noble gases have stable electron
configurations.
Draw Lewis dot structures for the
representative elements
 Valence
electrons determine the chemical
properties of an element.
 A Lewis dot structure (LDS) is a model of an
atom that shows only the valence electrons in
the atom.
X
element symbol –
surrounded by
valence electrons
Practice drawing LDS
 sodium
 barium
Practice drawing LDS
 krypton
 sulfur
Practice drawing LDS
 nitrogen
 aluminum
Practice drawing LDS
 helium
1
2
13
14
15
16
17
18
Describe how an ionic bond forms
 Elements
“want” to have the same electron
configuration as their nearest noble gas
neighbor…because that is a stable electron
configuration.
 Some elements achieve stable electron
configurations by gaining or losing electrons.
 An ion is an atom that has lost or gained
electrons and now has a net charge.
 Remember…
 a
loss of electrons creates a positively charged ion,
a cation.
 a gain of electrons creates a negatively charged
ion, an anion.
 Remember…
 a
loss of electrons creates a positively charged ion,
a cation.
 a gain of electrons creates a negatively charged
ion, an anion.
 What
is the charge on an ion that has gained 3
electrons?
 Remember…
 a
loss of electrons creates a positively charged ion,
a cation.
 a gain of electrons creates a negatively charged
ion, an anion.
 What
is the charge on an ion that has lost 2
electrons?
 A chemical
bond is the force that holds atoms/
ions together.
 An ionic bond is a chemical bond that forms
due to a charge attraction after electrons have
been transferred between atoms.
 Remember that opposite charges attract…
 when
cations and anions get close enough to each
other, an ionic bond forms.
Predict the composition of an ionic
compound
 Ionic
compounds contain ionic bonds and will
have a net charge of zero on the compound.
 The charges on the ions formed by sodium and
chlorine cancel each other out in a 1:1 ratio, so
only one ion of each type is needed for the
chemical formula.
 What
is the chemical formula when magnesium
combines with chlorine?
 Magnesium
has two electrons to lose, but chlorine
can only gain one electron.
 What
is the chemical formula when magnesium
combines with chlorine?
 Magnesium
has two electrons to lose, but chlorine
can only gain one electron.
 What
is the chemical formula when magnesium
combines with chlorine?
 What
is the chemical formula when magnesium
combines with chlorine?
 Therefore,
the chemical formula is
 What
is the chemical formula when cesium
combines with iodine?
 What
is the chemical formula when potassium
combines with nitrogen?
 What
is the chemical formula when aluminum
combines with chlorine?
 What
is the chemical formula when calcium
combines with phosphorus?
Relate the properties of ionic compounds to the structure of crystal
lattices
 Chemical
formulas for ionic compounds only
give you the ratio of ions in the compound.
 Ionic compounds form crystals. The shape of
the crystal depends on the arrangement of the
ions.
 The arrangement of the ions depends on the
ratio of ions and their relative size (the size of
the charges).
 This
crystal structure is what makes ionic
compounds brittle.
 The close packing in crystals can be explained
by the strong attractions in ionic compounds.
 The strong ionic bonds also explain the high
melting points of ionic compounds. It takes
more energy to get those strong attractions to
release and melt.
 Those strong attractions also explain why the
solid form does not conduct electricity.
However, once the solid is melted or dissolved
in water, ionic compounds are very good
conductors of electricity.