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

_{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:

Lattice Enthalpy: Atomisation and Bond Dissociation

Lattice Enthalpy: Electron Affinity

Exothermic and Endothermic Electron Affinity

Alternative Born-Haber Cycles (article)

Labelling Enthalpy Changes (article)

Perfect Ionic Model: Covalent Character

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## Constructing Born-Haber Cycles

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

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

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

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^{–} → N^{2-} (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 [N^{2-} + e^{– } → N^{3-}(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^{–} → S^{2-}(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.