Lesson 9: Understanding
Ionic Bonding
Unit:
Lesson Objectives:
1. strong electrostatic attraction between
oppositely charged ions.
2. effects ionic radius and ionic charge have
on the strength of ionic bonding.
3. formation of ions in terms of electron loss
or gain.
4. electronic configuration diagrams of cations
and anions
Ionic Bonding
Theory:
Tutor Presentation
• Ions are electrically charged particles formed when atoms lose or gain electrons. They have the
same electronic structures as noble gases.
• Metal atoms form positive ions by loosing electrons , while non-metal atoms form negative ions by
gaining electrons.
• e.g. Na+, Cl-, Mg2+, O2- etc .
• If negative electrons are lost the excess charge from the protons produces an
overall positive ion. If negative electrons are gained there is an excess of
negative charge, so a negative ion is formed.
• The strong electrostatic forces of attraction between oppositely charged ions are called ionic
bonds.
Theory:
Tutor Presentation
Ionic Bonding
Ionic bonding is the result of electrostatic attraction between
oppositely charged ions, extending through the compound, so that
every negatively charged ion attracts every positively charged ion and
visa versa.
Ionic compounds always exist in a structure that is called a lattice.
Theory:
Tutor Presentation
Ionic bonding in MgCl2
Supervised Learning
Draw dot cross diagrams to show how
CaCl2 is formed
Ionic Bonding
Theory:
Tutor Presentation
The ions stick together due to an
electrostatic attraction between
the positive and negative charges.
1s22s22p63s1 1s22s22p63s23p5
The sodium atom loses its 3s
electron to the chlorine atom.
The sodium becomes a sodium 1+
ion and the chlorine becomes a
chlorine 1- ion.
1s22s22p6
1s22s22p63s23p6
Theory:
Tutor Presentation
Ionic bonding and orbitals
Ionic bonding and orbitals
Theory:
Tutor Presentation
• Example 1: Sodium Chloride (NaCl)
1s22s22p63s1



1s22s22p63s23p5
1s22s22p6 1s22s22p63s23p6
2:8:1
2:8:7
2:8
2:8:8
An electron is transferred from the 3s orbital of sodium to the 3p orbital of
chlorine; both species end up with the electronic configuration of the nearest
noble gas the resulting ions are held together in a crystal lattice by electrostatic
attraction
What are the ionic equations?
What about the bonding in MgCl2?
Theory:
Tutor Presentation
Giant Ionic Crystal Lattice
Each Na+ is surrounded by 6 Cl¯
(co-ordination number = 6)
Each Cl¯ is surrounded by 6 Na+
(co-ordination number = 6)
Ionic Radius and bond strength
Theory:
Tutor Presentation
• A warning!
• Ionic radii are difficult to measure with any degree of certainty, and vary according to
the environment of the ion. For example, it matters what the co-ordination of the ion is
(how many oppositely charged ions are touching it), and what those ions are.
• There are several different measures of ionic radii in use, and these all differ from each
other by varying amounts. It means that if you are going to make reliable comparisons
using ionic radii, they have to come from the same source.
• What you have to remember is that there are quite big uncertainties in the use of ionic
radii, and that trying to explain things in fine detail is made difficult by those
uncertainties.
Theory:
Tutor Presentation
What is Ionic Radius?
• The radius of cation or anion is called as ionic radius. In the
formation of cation, we remove electrons from an atom. It decreases
the number of electrons and increases the number of protons
compare to electrons. In other words we can say that the nuclear
attraction forces increases in cation and it reduces the ionic radii
compare to neutral atom.
• On the contrary, in anion, we add one or more electrons to the
valence shell which reduces the nuclear attraction force that results
inc
What is Ionic Radius?
Theory:
Tutor Presentation
• Ionic radius can be defined as the radius of ions, when it is bonded with
another ion. Like atomic radius, it is difficult to measure the ionic radius
also. We can observe the difference in size of cation and anion compare to
their respective atoms.
• The formation of sodium ion from sodium atom (2, 8, 1) changes the
electronic configuration to 2, 8. Hence 10 electrons are being pulled in by
the full force of 11 protons that reduces the ionic radius. In case of
negative ion like chloride ion, the electronic configuration changes from 2,
8, 7 to 2, 8, 8. Hence there are only 17 protons to hold 18 electrons. It
increases the ionic radius.
Theory:
Tutor Presentation
Theory:
Tutor Presentation
Trends in ionic radius down a group
• As you add extra layers of
electrons as you go down a
group, the ions are bound to get
bigger.
• The strength of electrostatic
attraction decreases with
increasing size of ionic radi
Theory:
Tutor Presentation
Trends in ionic radius across a period
Na+
Mg2+
Al3+
no of
protons
11
12
electronic
structure
of ion
2,8
ionic
radius
(nm)
0.102
P3-
S2-
Cl-
13
15
16
17
2,8
2,8
2,8,8
2,8,8
2,8,8
0.072
0.054
(0.212)
0.184
0.181
Within the series of positive ions, and the series of negative ions, that the ionic radii fall as you go across the
period.
The positive ions - the ions have exactly the same electronic structure - they are said to be isoelectronic.
However, the number of protons in the nucleus of the ions is increasing. That will tend to pull the electrons
more and more towards the centre of the ion - causing the ionic radii to fall.
The negative ions - Exactly the same thing is happening here, except that you have an extra layer of electrons
Physical Properties
• Melting point very high
Theory:
Tutor Presentation
A large amount of energy must be put in to overcome the strong
electrostatic attractions and separate the ions.
• Strength Very brittle
Any dislocation leads to the layers moving and similar ions being
adjacent. The repulsion splits the crystal.
-
+
-
+
+
-
+
-
-
+
-
+
-
+
-
+
Physical Properties
• Melting point very high
Theory:
Tutor Presentation
A large amount of energy must be put in to overcome the strong
electrostatic attractions and separate the ions.
• Strength Very brittle
Any dislocation leads to the layers moving and similar ions being
adjacent. The repulsion splits the crystal.
-
+
-
+
+
-
+
-
-
+
-
+
-
+
-
+
Physical Properties
Theory:
Tutor Presentation
• Electrical
Don’t conduct when solid - ions held strongly in the lattice conduct
when molten or in aqueous solution - the ions become mobile and
conduction takes place.
Cl-
Na+
ClNa+
Cl-
Na+
ClNa+
ClNa+
Cl-
Na+
Cl-
Cl-
Na+
ClNa+
Na+
Na+
ClDISSOLVING AN IONIC COMPOUND
IN WATER BREAKS UP THE
STRUCTURE SO IONS ARE FREE TO
MOVE TO THE ELECTRODES
Required Reading
• http://chemguide.co.uk/atoms/bonding/ionic.html#top
• http://chemguide.co.uk/atoms/structures/ionicstruct.html#top