Ionic bonding occurs between metal and non-metal atoms when they form ions. Metals form positive ions by losing electrons, filling their outer electron shells. Non-metals form negative ions by gaining electrons. The oppositely charged ions are attracted in an ionic compound via electrostatic forces. Sodium chloride is an example where sodium atoms lose electrons to become Na+ ions and chloride atoms gain electrons to become Cl- ions. The ions are arranged in a crystal lattice structure held together by ionic bonds.

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What are bonds?
Compounds are formed when different elements chemically
react and form bonds with each other.
Some compounds, like water (H20),
have small, simple structures with
just a few atoms bonded together.
Others compounds, like DNA, have large, complex structures
containing thousands or even millions of bonded atoms.
Elements are the simplest substances that exist on Earth.
Each element is made up of just one type of atom, usually
joined to other atoms of the same element by bonds.
This forms molecules such as chlorine (Cl2).

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Why do atoms form bonds?
Bonds involve the electrons in the outer shells of atoms.
Filled electron shells are very stable.
1st shell holds a maximum
of 2 electrons
2nd shell holds a maximum
of 8 electrons
3rd shell holds a
maximum of 8 electrons
Each shell has a maximum number of electrons that it can
hold. Electrons fill the shells nearest the nucleus first.

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Why do atoms form bonds?
The atoms of noble gases have completely
full outer shells and so are stable.
The atoms of other elements have
incomplete outer electron shells
and so are unstable.
This makes the noble gases very unreactive
and so they do not usually form bonds.
By forming bonds, the atoms of these
elements are able to have filled outer
shells and become stable.

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What are the types of bonding?
Different types of bonds are formed depending on the types
of atoms involved:
All bonds involve electrons and all bonding involve changes
to the number of electrons in the outer shells of atoms.
 ionic bonding
– occurs between metal and non-metal atoms.
 covalent bonding
– occurs between non-metals atoms only.
 metallic bonding
– occurs between metal atoms only.
How do you think electrons are involved in ionic bonding?

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From atoms to ions
How can reactive metal atoms become stable positive ions?

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How do atoms form ions?
An ion is an atom or group of atoms that has
an electrical charge, either positive or negative.
Atoms have an equal number of protons and electrons and
so do not have an overall charge.
Atoms with incomplete outer electron
shells are unstable. By either gaining or
losing electrons, atoms can obtain full
outer electron shells and become stable.
When this happens, atoms have an unequal number of
protons and electrons and so have an overall charge.
This is how atoms become ions.
How does an atom become a positive or negative ion?

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Positive and negative ions?
The electron configuration of an atom shows how many
electrons it must lose or gain to have a filled outer shell.
An atom that loses electrons has more protons
than electrons and so has a positive overall charge.
This is called a positive ion.
An atom that gains electrons has more electrons
than protons and so has a negative overall charge.
This is called a negative ion.
 Atoms with a nearly empty outer shell, will lose electrons
to obtain a full outer shell.
 Atoms with a nearly full outer shell, will gain electrons
to obtain a full outer shell.

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How do atoms form positive ions?
An atom that loses one or more electrons
forms a positive ion.
Positive ions have a small ‘+’ symbol and a number by this
to indicate how many electrons have been lost.
This number is usually the same as the number of electrons
in the atom’s outer shell. For example:
Metal atoms, such as sodium, magnesium
and iron, form positive ions.
lithium ion [ 2 ]
lithium atom 2.1
aluminium atom 2.8.3 aluminium ion [ 2.8 ]
magnesium atom 2.8.2 magnesium ion [ 2.8 ] = Mg2+
= Li+
= Al3+

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How is a sodium ion formed?
2.8.1
(partially full outer shell)
11 protons = +11
11 electrons = -11
Total charge = 0
Sodium atom:
11 protons = +11
10 electrons = -10
Total charge = +1
Sodium ion:
loses
1 electron
+
[2.8]
(full outer shell)
Na Na

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How is a magnesium ion formed?
2.8.2
(partially full outer shell)
12 protons = +12
12 electrons = -12
Total charge = 0
Magnesium atom:
12 protons = +12
10 electrons = -10
Total charge = +2
Magnesium ion:
[2.8]2+
(full outer shell)
2+
Mg Mg
loses
2 electrons

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How do atoms form negative ions?
Negative ions have a small ‘-’ symbol and a number by this
to indicate how many electrons have been gained to fill their
outer shell. For example:
An atom that gains one or more electrons
forms a negative ion.
The name of the ion is slightly different to the atom’s name.
Non-metal atoms, such as chlorine,
oxygen and nitrogen, form negative ions.
chlorine atom chloride ion [ 2.8.8 ] = Cl-
oxygen atom oxide ion [ 2.8 ]
nitrogen atom nitride ion [ 2.8 ]
2.8.7
2.6
2.5 = N3-
= O2-

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How is a fluoride ion formed?
2.7
(partially full outer shell)
9 protons = +9
9 electrons = -9
Total charge = 0
Fluorine atom:
9 protons = +9
10 electrons = -10
Total charge = -1
Fluoride ion:
[2.8]-
(full outer shell)
-
F F
gains 1
electron

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[2.8.8]2-
(full outer shell)
2.8.6
(partially full outer shell)
How is a sulfide ion formed?
16 protons = +16
16 electrons = -16
Total charge = 0
Sulfur atom:
16 protons = +16
18 electrons = -18
Total charge = -2
Sulfide ion:
2-
S S
gains 2
electrons

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Building an ion

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Calculating ion charges
What is the charge on the ion of each element?
+2 +2
+1 -3 -1
2.8.8.2 1 2.8.5 2.7 2.2
calcium hydrogen phosphorus fluorine beryllium
Element
Electron
shells
Charge
on ion

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Electron configuration of ions
The number of protons and neutrons however, remain
different for each element.
This means that each ion has different properties.
For example, oxygen and fluorine both gain electrons to
become negative ions. The resulting ions have the same
electron configuration:
F
-
2-
O
When different elements gain or lose electrons to complete
their outer electron shell, they can create ions that have the
same electron configuration.

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Comparing electron configurations

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What is a compound ion?
Ions can be made up of a single atom or a group of atoms. An
ion made up of a group of atoms is called a compound ion.
hydroxide
sulfate
nitrate
carbonate
ammonium
-1
-2
-1
-2
+1
Ion Formula Charge Atoms present
NH4
+
CO3
2-
NO3
-
SO4
2-
OH-
O
O O
O
O
O O O
O
O
O
H
H H H
H
C
N
N
S
What atoms are present in the following compound ions?

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Comparing positive and negative ions

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Ions and attraction
Why do some ions attract while others repel?

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What is ionic bonding?
Compounds that contain ions are called ionic
compounds. These compounds are usually
formed by a reaction between a metal and a
non-metal.
Why do these substances react together and form bonds?
The metal and non-metal atoms have incomplete outer
electron shells and so are unstable.
Electrons are transferred from each metal atom to each
non-metal atom. The metal and the non-metal atoms form
ions with completely full outer shells and become stable.
The positive and negative ions are strongly attracted to each
other. This electrostatic attraction is called ionic bonding.

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How are ionic bonds formed?
Sodium chloride is an ionic compound formed by the reaction
between the metal sodium and the non-metal chlorine.
Sodium has 1 electron
in its outer shell.
Chlorine has 7 electrons
in its outer shell.
2.8.7 [2.8.8]-
+
Cl Cl
-
2.8.1 [2.8]+
Na Na
By losing this electron,
it has a filled outer shell
and forms a positive ion.
By gaining an electron
from sodium, it has a
filled outer shell and
forms a negative ion.

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How are ionic bonds formed?
The positive sodium ions and the negative chloride ions
are strongly attracted to each other.
-
Cl
It is this electrostatic attraction that forms ionic bonds in
sodium chloride and other ionic compounds.
Na
+

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Formation of an ionic bond

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Ions and ionic bonding – summary

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What is the ratio of ions?
Sodium chloride (NaCl) and magnesium oxide (MgO) are
simple ionic compounds.
Both compounds have a 1:1 ratio of metal ions to non-metal
ions, which is shown by the formula of each compound.
Na Cl Na+ Cl-
1 electron
Mg Mg2+
O O2-
2 electrons
In each compound, the metal needs to lose the same
number of electrons that the non-metal needs to gain.

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What is the ratio of ions in sodium oxide?
What is the ratio of ions needed to make sodium oxide?
Sodium (2.8.1) needs to lose 1 electron to form a sodium ion
but oxygen (2.6) must gain 2 electrons to form an oxide ion .
Na
Na
O O2-
Na+
Na+
1 electron
from each
Na atom
Two sodium atoms are required for each oxygen atom
and so the ratio of sodium ions to oxide ions is 2:1.
From this ratio, the formula of sodium oxide is Na2O.

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What is the ratio of ions in magnesium chloride?
What is the ratio of ions needed for magnesium chloride?
Magnesium (2.8.2) needs to lose 2 electrons to form a
magnesium ion but chlorine (2.8.7) needs to gain 1 electron
to form an chloride ion.
Mg
Cl
Mg2+
Cl
Cl-
Cl-
1 electron
for each
Cl atom
Two chlorine atoms are required for each magnesium atom
and so the ratio of magnesium ions to chloride ions is 1:2.
From this ratio, the formula of magnesium chloride is MgCl2.

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How to write the formula of an ionic compound
To work out the formula of an ionic compound:
1. Write down the symbol for each element
– the metal is always written first.
2. Calculate the charge for each type of ion.
3. Balance the number of ions so that the positive
and negative charges are balanced and equal zero.
This gives the ratio of ions.
4. Use the ratio to write down the formula of the ionic
compound.
The formula of a compound uses chemical symbols and
numbers to show the ratio of atoms of each element present.

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Formula of aluminium bromide
What is the formula of aluminium bromide?
Al Br
+3 -1
AlBr3
3 bromide ions are needed
for each aluminium ion
1 : 3
Symbol
Balance the
number of ions
Ion charge
Ratio of ions
Formula
Al
Br
Al3+
Br
Br
Br
-
Br
-
Br
-
1 electron
for each
bromine
atom

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Formula of aluminium oxide
What is the formula of aluminium oxide?
Al O
+3 -2
Al2O3
2 aluminium ions are
needed for 3 oxide ions
2 : 3
Symbol
Balance the
number of ions
Ion charge
Ratio of ions
Formula
Al Al3+
Al
Al3+
O O2-
O O2-
O O2-
2 electrons for
each oxygen atom

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More ionic formulae
What are the formulae of all the possible ionic compounds
from combinations of these metals and non-metals.
metals
non-
metals
Li Ca Na Mg Al K
F
O
N
Br
S
Cl
LiF CaF2 NaF MgF2 AlF3 KF
Li2O CaO Na2O MgO Al2O3 K2O
Li3N Ca3N2 Na3N Mg3N2 AlN K3N
LiBr CaBr2 NaBr MgBr2 AlBr3 KBr
Li2S CaS Na2S MgS Al2S3 K2S
LiCl CaCl2 NaCl MgCl2 AlCl3 KCl

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What is the ionic formula?

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What is an ionic lattice?
In an ionic compound, millions and millions of ions are
packed together in a regular cubic arrangement, joined by
ionic bonds.
The structure of the ionic
lattice affects the properties
of the ionic compound.
The ionic lattice will
continue to build in this way
until there are no more ions
left to add.
This forms a giant 3D
structure called an
ionic lattice.

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Why do ionic compounds form crystals?
Ionic compounds such as sodium chloride, form crystals, with
a cubic shape. This is due to the structure of the ionic lattice.
All ionic compounds form lattices and crystals when solid.

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Heating ionic compounds
Why are ionic compounds solid at room temperature and
have high melting points and boiling points?
Larger ionic charges produce stronger ionic bonds and so
much more heat is required to break the ionic bonds in
magnesium oxide than in sodium chloride.
sodium chloride
magnesium oxide
Compound
Ion
charges
Melting
point (oC)
Boiling
point (oC)
1+ and 1-
2+ and 2-
801 1,413
2,852 3,600
strong
ionic bonds
hold ions
together
Ionic bonds are strong and a
lot of heat is needed to break
them.

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Do ionic compounds conduct electricity?

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How can ionic compounds conduct electricity?
When liquid (molten), the ions
can break free of the lattice
and are able to move. The ions
are charged particles and so
can carry an electric current.
As solids, ionic compounds
cannot conduct electricity
because their ions are
bonded together in the lattice.
ions in
solid state
cannot
move
ions in
molten state
can move
and conduct
electricity
Ionic compounds are usually soluble in water because water
molecules have a slight electrical charge and so can attract
the ions away from the lattice. When dissolved, the ions are
free to move and can carry an electric current.

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Why are ionic compounds brittle?
Ionic compounds are brittle – they shatter when they are hit.
When the lattice is hit, a layer
of ions is shifted so that ions
with the same charges are
lined up together.
These like charges repel
each other and so split
the ionic lattice causing
it to shatter.
repulsion
force
Ionic bonds are strong, so why does this happen?

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True or false?

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Glossary
bond – A strong force that joins atoms or ions together in
molecules and giant lattices.
compound ion – An ion made up of a group of atoms,
rather than one single atom.
ionic bond – The electrostatic force of attraction between
oppositely charged ions.
ionic compound – A compound made up of ions.
ionic lattice – A giant 3D structure of closely packed,
oppositely-charged ions.
negative ion – An atom or group of atoms that has gained
electrons and so has a negative charge.
noble gas – An element that has a full outer electron shell
and so is very stable and unreactive.
positive ion – An atom or group of atoms that has lost
electrons and so has a positive charge.

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Anagrams

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Multiple-choice quiz