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
Transcript
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
Ionisation Energy• 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 :
• A (g) → A (g) + e
• What will be the Ionisation energy equation for Sodium atom?
• Na (g) → Na (g) + e
+ _
+ _
The energy to remove the first electron is called the first Ionisation energyfirst Ionisation energy
Will Ionisation energy be ENDOTHERMIC OR
EXOTHERMIC process?
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).
• Na (g) → Na (g) + e + 2+ _
I.E. = 4563kJ/mol
First ionization energy of sodium
Second ionization energy of sodium
Comparison of first and second ionization energies 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 BohrAtomic Line Emission
Spectra and Niels Bohr• 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.
Niels BohrNiels Bohr
(1885-1962)(1885-1962)
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.
Energy transition in Hydrogen atom
EnergyWhen ‘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.
GROUND STATE
EX
CIT
ED
ST
AT
E
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 LevelsEnergy LevelsEnergy LevelsEnergy Levels
n = 1n = 1
n = 2n = 2
n = 3n = 3
n = 4n = 4
Successive ionization energies
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
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. 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
Aluminium – Al- 13Group 3
Ionisation energy increases for electron 1,2 and 3. Electrons are present in the same shell (n=3)
Ionisation energy increases remarkably for electron 4 and 12. Electrons are present in the different shells (n=1,2,3)
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
2.8.3
Line Spectra of Other Line Spectra of Other ElementsElements
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 is divided into subshells. These subshells are described by letters: s,p,d,f.
Shell Subshells
1 1s
2 2s, 2p
3 3s, 3p, 3d
4 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.
Arrange all the subshells in an increasing order of energy.
Diagonal Rule
ss
s 3p 3ds 3p 3d
s 2ps 2p
s 4p 4d 4fs 4p 4d 4f
s 5p 5d 5f 5g?s 5p 5d 5f 5g?
s 6p 6d 6f 6g? 6h?s 6p 6d 6f 6g? 6h?
s 7p 7d 7f 7g? 7h? 7i?s 7p 7d 7f 7g? 7h? 7i?
11
22
33
44
55
66
77
Steps:Steps:
1.1. Write the energy levels top to bottom.Write the energy levels top to bottom.
2.2. Write the orbitals in s, p, d, f order. Write the orbitals in s, p, d, f order.
3.3. Write the same number of orbitals as the Write the same number of orbitals as the energy level.energy level.
4.4. Draw diagonal lines from the top right to Draw diagonal lines from the top right to the bottom left.the bottom left.
5.5. To get the correct order, To get the correct order,
follow the arrows!follow the arrows!
By this point, we are past By this point, we are past the current periodic table the current periodic table so we can stop.so we can stop.
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.
Ionization Energy: Periodic table
Atomic number
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.
Ionisation Energy increases as the number of electrons removed increases (1)Large amount of energy difference in 1 & 2 indicate that these electrons are present in different shells. Similarly electron 9 and 10 are present in different shell. (1)Atom has three shells.1 electron is present in outermost shell, 8 electrons in the next shell and 2 electron in the innermost shell. 1s 2s 2p 3s (1)
3 marks
2 2 6 1
If an atom has one valence electron eg Na,
which group does it belong to?
Review of lesson
Homework
• Homework task: Complete question 1 and 2 on page 61 of Edexcel active book.
