Up Learn – A Level Chemistry (aqa) – Constructing Born-Haber Cycles

Lattice Enthalpy: Electron Affinity

Electron affinities are defined as the enthalpy changes when one mole of electrons is added to one mole of gaseous atoms/ions.

More videos on Constructing Born-Haber Cycles:

Summary of Lattice Enthalpy

Lattice Enthalpy: Atomisation and Bond Dissociation

Lattice Enthalpy: Electron Affinity

Summary of Born Haber Cycles

Exothermic and Endothermic Electron Affinity

Alternative Born-Haber Cycles (article)

Labelling Enthalpy Changes (article)

Perfect Ionic Model: Covalent Character

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Up Learn – A Level Chemistry (AQA)

Constructing Born-Haber Cycles

1. Introduction to Lattice Enthalpies
2. Enthalpies Recap
3. Lattice Enthalpy
4. Predicting Lattice Enthalpies
5. Finding Lattice Enthalpy Experimentally
6. Finding Lattice Enthalpy Using a Hess Cycle
7. Separation
8. Atomisation
9. Atomisation and Bond Dissociation
10. Removing Electrons
11. Adding Electrons
12. Electron Affinity
13. Representing Different Enthalpy Changes
14. Summary of the Alternate Route
1. The Aftermath of WWI
2. Exo or Endo?
3. Exothermic and Endothermic Electron Affinity
4. Constructing Born Haber Cycles: First Steps
5. Constructing Born Haber Cycles: Adding Atomisation
6. Constructing Born Haber Cycles: Removing Electrons
7. Constructing Born Haber Cycles: Adding Electrons
8. Alternative Born-Haber Cycles
9. Labelling Enthalpy Changes
10. Labelling Born-Haber Cycles
11. Constructing Born-Haber Cycles
12. Finding Lattice Enthalpy using Born-Haber Cycles
13. Calculating Lattice Enthalpies using Born-Haber Cycles
14. Constructing Born Haber Cycles: Adding More Than One Electron
15. Calculating Lattice Enthalpy Using More Complex Born-Haber Cycles
16. Calculating Enthalpies Other Than Lattice Enthalpy Using Born-Haber Cycles
1. Theoretical vs Experimental Lattice Enthalpies – Introduction
2. Calculating Lattice Enthalpies Quickly
3. Theoretical vs Experimental
4. Perfect Ionic Model: Covalent Character
5. Polarisation
6. Polarising Power
7. Polarisability
8. Comparing Covalent Character
9. The Curious Case of the Silver Halides
1. An Alternative Route For Lattice Enthalpy
2. Dissolving Salts In Water
3. The Enthalpy of Solution
4. Enthalpy Changes and The Enthalpy of Solution
5. Can I Feel The Enthalpy of Solution?
6. Gaseous Ion Hydration
7. Enthalpy of Hydration
8. Factors Affecting the Enthalpy of Hydration
9. Constructing an Alternative Route for Lattice Enthalpy
10. Calculating Lattice Enthalpy
11. Energy Level Diagrams, Hydration and Solution
12. Energy Level Diagrams and Exothermic Enthalpies of Solution
13. Converting SHL Cycles into Energy Level Diagrams

Last time we saw that the fourth and final step of our alternative route was adding electrons

But…. while we’ve seen how to calculate the enthalpy change of removing electrons using first ionisation energy

We haven’t seen an equivalent measurement for adding electrons…

So, we define the first electron affinity as the enthalpy change when one mole of electrons is added to one mole of gaseous atoms 

And we represent it like this [N(g) + e– → N– (g)]

We define the second electron affinity as the enthalpy change when one mole of electrons is added to one mole of gaseous ions with a one minus charge

We represent it like this [N– (g) + e– → N2- (g) ]

And, we define the third electron affinity as… 

As the enthalpy change when one mole of electrons is added to one mole of gaseous ions with a two minus charge

And we represent it like this [N2- + e–  → N3-(g) ]

Now, just like ionisation energies, chemists also have access to tables of data on electron affinities

And that means we can use them to calculate the enthalpy change of adding electrons 

So the enthalpy change of this reaction [Cl(g) + e– → Cl– (g)] is equal to the 1st electron affinity of chlorine

The enthalpy change of this reaction [S(g) + 2e– → S2-(g)] is equal to the electron affinity of sulfur plus the second electron affinity of sulfur

And the enthalpy change of this reaction is equal to 

The enthalpy change of this reaction is equal to the electron affinity of nitrogen plus the second electron affinity of nitrogen, plus the third electron affinity of nitrogen.

So, to sum up…

Chemists calculate the enthalpy change of adding electrons using electron affinities.

The first electron affinity is defined like this.

And we represent it like this.

And the second electron affinity is defined like this.

And we represent it like this.
And subsequent electron affinities, like the third fourth fifth sixth and so on, follow a similar pattern.