Ionization energy
d. recall and understand the definition of ionization energies of gaseous atoms
and that they are endothermic processes
e. recall that ideas about electronic structure developed from:
i. an understanding that successive ionization energies provide evidence
for the existence of quantum shells and the group to which the element
belongs
ii. an understanding that the first ionization energy of successive elements
provides evidence for electron sub-shells
Connector:
The mass spectrum for zirconium
Given that the percentage abundance of
its isotopes is:
• zirconium-90
51.5
• zirconium-91
11.2
• zirconium-92
17.1
• zirconium-94
17.4
• zirconium-96
2.8
Calculate the relative atomic mass of
zirconium
Will Ionisation energy be
Ionisation Energy
ENDOTHERMIC OR
EXOTHERMIC process?
• It is the amount of energy required
to
remove a mole of electrons from a mole of
gaseous atoms or ions.
• Ionisation energy is measured in kJ/mole.
• It can be represented as : The energy to remove the
+
_
first electron is called the
• A (g) → A (g) + e
first Ionisation energy
• What will be the Ionisation energy
equation for Sodium atom?
+
_
• Na (g) → Na (g) + e
I.E. = 496 kJ/mol
Ionisation Energy
• In simple terms, Ionisation energy is the
measure of how tightly or loosely the outer
electron is attracted to the nucleus.
• The less tightly it is bound, more reactive the
element will be.
• The Second Ionisation energy is the amount of
energy required to remove a mole of electrons
from a mole of gaseous cations (+ charged).
+
2+
• Na (g) → Na (g) + e
_
I.E. = 4563kJ/mol
Comparison of first and second ionization energies of sodium
First ionization energy of sodium
Second ionization energy of sodium
Notice the large difference in I.E. values.
Suggest why this is so.
Write an expression for the third ionization
energy of sodium and predict its value.
Atomic Line Emission
Spectra and Niels Bohr
Niels Bohr
(1885-1962)
• Bohr’s greatest contribution to
science was in building a simple
model of the atom.
• If a gas is heated or an electric
charge is passed through it, the gas
gives out light.
• If you pass the light through a prism,
the light splits to give a spectrum.
• The spectrum is made up of a series
of separate lines or bands called Line
spectrum or Emission spectrum.
Spectrum of
Excited Hydrogen Gas
Bohr used the hydrogen spectrum to
suggest that electrons are
arranged in shells around the
nucleus.
Each shell represents a different
energy level.
Moving out from the centre of the
atom, successive shells become
closer together, in the same way
as the energy levels in the line
spectrum become closer.
EXCITED STATE
Energy transition in Hydrogen atom
Energy
GROUND STATE
When ‘H’ atoms are heated, electrons are
promoted from the GROUND STATE (low
energy, highly stable) to EXCITED STATE
(high energy, least stable) . Being
UNSTABLE, electron drops back, giving out
the energy gained in the form of LIGHT.
Principal Quantum number (n)
 In an Atom, electrons
are arranged in a series
of shells. Each shell is
described by a number
called PRINCIPAL
QUANTUM NUMBER
(n).
 The larger the value of
‘n’, the further the
electron will be from
nucleus.
Energy Levels
n=1
n=2
n=3
n=4
Ionisation
Ionisation energy
energy increases
increases remarkably
for electron
Aluminium
– are
Al13 are
for
1,2electron
and
3. Electrons
4 and 12.
Electrons
present
in the
Successive
ionization
energies
Group
3
present
same shell
in the
(n=3)
different shells (n=1,2,3)
The table below shows the successive ionisation energy
(kJ/mole) of an atom. Numbers from 1 to 13 show the
ionisation energy for the corresponding number of electrons
1
2
3
580
1820
2750
4
5
6
7
8
9
10
11
11600
14800
18400
23300
27500
31900
38500
42700
12
13
200 000 222 000
1. Name the atom and it’s group.
2. Explain the relative magnitude of the first, second and third
ionisation energy.
3. Explain the relative magnitude of the first, fourth and twelfth
ionisation energy
2.8.3
1
2
3
580
1820
2750
4
5
6
7
8
9
10
11
11600
14800
18400
23300
27500
31900
38500
42700
12
13
200 000 222 000
Line Spectra of Other
Elements
Unfortunately, this simple interpretation of line spectrum
of Hydrogen did not explain the complex spectra of other
elements. This lead to the suggestion that shells can be
divided into sub-shells.
Sub-shells
• Each shell
Arrange
is divided
all theinto
subshells
subshells.
in anThese
subshells
increasing
are described
order ofby
energy.
letters: s,p,d,f.
Shell Subshells
1
1s
2
3
4
2s, 2p
3s, 3p, 3d
4s, 4p, 4d, 4f
Subshells have different
energies.
s (lowest energy)< p< d< f
As the ‘n’ increases, the energy gap between successive
shells decreases. As a result, neighbouring subshells
overlap and have a different order of increasing energy in
subshells.
Diagonal Rule
Steps:
1s
2s
3s
2p
3p
3d
1.
Write the energy levels top to bottom.
2.
Write the orbitals in s, p, d, f order.
3.
Write the same number of orbitals as the
energy level.
4.
Draw diagonal lines from the top right to
the bottom left.
5.
To get the correct order,
follow the arrows!
4s
4p
4d
4f
5s
5p
5d
5f
5g?
6s
6p
6d
6f
6g?
6h?
7s
7p
7d
7f
7g?
7h?
By this point, we are past
the current periodic table
so we can stop.
7i?
Electronic configuration
Maximum number of electrons in
‘s’ can be 2 and ‘p’ can be 6.
Write down the
electronic
configuration of
Magnesium and
Aluminium.
Ionisation energy along a period increases as it is difficult to remove
electrons from same shell with increasing effective nuclear charge.
But there are some exceptions like B and Al. Look at their electronic
configuration and explain the lowering of Ionisation energy.
Ionization Energy: Periodic table
Atomic number
Ionisation Energy increases as the number of electrons removed increases (1)
Large amount of energy difference in 1 & 2 indicate that these electrons are
If an atom has one
present in different shells.
Similarly electron 9 and 10 are present in different
valence electron eg Na,
shell. (1)
which group does it
Atom has three shells.1 electron
is to?
present in outermost shell, 8 electrons in
belong
2
2
6
1
the next shell and 2 electron in the innermost shell. 1s 2s 2p 3s
(1)
3 marks
Review of lesson
Homework
• Homework task: Complete question 1 and 2 on
page 61 of Edexcel active book.
• Due date: next lesson
• Criteria for Grade C:
• Criteria for Grade B:
• Criteria for Grade A: