Homework Private study work (bring notes to show me next lesson); Read pages 40 – 41 in your text book and complete the practice questions on each double page spread Look at the following website Topic 1, concentrate on ionisation energies

AS Chemistry Electron Structure Lesson 1 Ionisation Energies

Unit Objectives Electron structure This is split into two parts: Ionisation Energies Electrons – Electronic Energy Levels, – Atomic Orbitals, – Electronic Structure

Lesson Objectives Ionisation Energies (a) Define the terms first ionisation energy and successive ionisation energy; (b) Explain that ionisation energies are influenced by nuclear charge, electron shielding and the distance of the outermost electron from the nucleus; (c) predict from successive ionisation energies of an element: – (i) the number of electrons in each principal quantum shell of an atom, – (ii) the group of the element;

Exam question Answer the exam question below. Some of the questions may be new to you. We will look at these ones later in the lesson. Some are linked to GCSE work, and we will look at those in more detail later in the module. C Al N Mg

Definitions Can anyone give definitions of: First ionisation energy Successive ionisation energy

Definitions First ionisation energy The first ionisation energy of an element is the energy required to remove one electron from each atom of one mole of gaseous atoms to form one mole of gaseous 1+ ions. Write an equation for the 1 st ionisation of sodium i.e. (note state symbols must be included) Na (g)  Na + (g) + e - 1st I.E. = +496 kJ.mol -1

Ionisation Energy What affects ionisation energy? Any ideas? Electrons are held in their shells by their attraction to the positive nucleus. This attraction must be overcome to remove an electron. The outer electrons are furthest away as so they are least attracted. Therefore they are easiest to remove and are removed first.

Ionisation Energy The nuclear attraction is affected by three things: Any ideas? Atomic radius – Greater radius = less attraction. Nuclear charge – Larger charge = larger attraction. Electron shielding – Inner shells repeal electrons outside them, this is called shielding or screening. – More inner shells = lower attraction

Definition Electron shielding Electron shielding is the repulsion between electrons in different inner shells. Shielding reduces the net attractive force from the positive nucleus on the outer shell electrons.

The trends of first ionisation energies will be studied in more detail later in the module. In general it increases across a period and decreases down a group.

Exam questions Answer on white boards. A very common exam question, make sure you learn definitions!

Write an equation to represent the first ionisation energy of oxygen. [ 1 ] O (g)  O + (g) + e -

The trends of first ionisation energies will be studied in more detail later in the module.

Definitions Successive ionisation energy The successive ionisation energies are a measure of the energy required to remove each electron in turn. Write equations to show the 1 st, 2 nd and 3 rd ionisations of lithium (use whiteboards) E.g. Li (g)  Li + (g) + e - 1 st I.E. = +520 kJ.mol -1 Li + (g)  Li 2+ (g) + e - 2 nd I.E. = kJ.mol -1 Li 2+ (g)  Li 3+ (g) + e - 3 rd I.E. = kJ.mol -1

Definitions Successive ionisation energy The successive ionisation energies are a measure of the energy required to remove each electron in turn. What do you notice about the energy required for each successive ionisation energy? Li (g)  Li + (g) + e - 1 st I.E. = +520 kJ.mol -1 Li + (g)  Li 2+ (g) + e - 2 nd I.E. = kJ.mol -1 Li 2+ (g)  Li 3+ (g) + e - 3 rd I.E. = kJ.mol -1 Can you explain this trend?

Successive ionisation energy Each successive ionisation energy is greater. As each electron is removed there is less repulsion between the remaining electrons so they are drawn closer to the nucleus. As the distance decreases to the nucleus the electrons are held more strongly so more energy is required to remove them.

Electron Shells Looking at successive ionisation energies tells us 2 things: Some successive ionisation energies are close together, occasionally there is a large jump. This is evidence for discrete shells. We can also see the number of shells in each shell.

© Pearson Education Ltd 2008 This document may have been altered from the original Successive ionisation energies of nitrogen

Plotting the successive ionization energies of magnesium clearly shows the existence of different energy levels, and the number of electrons at each level. Successive ionization energies increase as more electrons are removed. Evidence for energy levels Large jumps in the ionization energy reveal where electrons are being removed from the next principal energy level, such as between the 2 nd and 3 rd, and 10 th and 11 th ionization energies for magnesium. electron removed ionization energy th 11 th 10 th 9 th 8 th 7 th 6 th 5 th 4 th 3 rd 2 nd 1 st

Exam question At the start of the lesson we looked at this exam question. Look at (v) again. Can you answer it? Can you explain your answer? C Al N Mg

Using ionisation energies to work out which group an element is in

Now Complete the exam questions on the worksheet

From Jan 2013, a different paper to earlier

2 marks

Look familiar? From Jan 2012

To finish off Answer on whiteboards 1.Write an equation to represent the 4 th ionisation energy of chlorine 2.Sketch the graph you would expect for the successive ionisation energies of aluminium 3.An element in period 3 (Na – Ar) has the following successive ionisation energies in kJ mol -1 : 789, 1577, 3232, 4356, 16091, 19785, 23787, Identify this element, giving your reasons.

Lesson Objectives Ionisation Energies (a) Define the terms first ionisation energy and successive ionisation energy; (b) Explain that ionisation energies are influenced by nuclear charge, electron shielding and the distance of the outermost electron from the nucleus; (c) predict from successive ionisation energies of an element: – (i) the number of electrons in each principal quantum shell of an atom, – (ii) the group of the element;