[LifeIsGood]

I'm not catching why it is negative? I've looked for lots of explanations and they say the electron being added is attracted to the nucleus but that doesn't explain why it is a negative enthalpy change? When I related back to the AS definition of exothermic - it is when a bond is formed so can a possible explanation be when an electron is added to the outer shell of an atom, a new bond is created leading to an exothermic change?

[charco]

(Original post by LifeIsGood)
I'm not catching why it is negative? I've looked for lots of explanations and they say the electron being added is attracted to the nucleus but that doesn't explain why it is a negative enthalpy change? When I related back to the AS definition of exothermic - it is when a bond is formed so can a possible explanation be when an electron is added to the outer shell of an atom, a new bond is created leading to an exothermic change?

A 'bond' is being formed between the electron and the nucleus. Bond formation leads to a more stable situation, so its an exothermic process.

[Enigma.]

Yeah so it's giving off energy so it matches whichever electron orbital its heading to occupy.

Imagine two cars are headed for a collision. One is positive and the other negative.

They crash. The crash gave off loads of energy (ie is exothermic) and the resultant situation is more stable (just a heap not moving at all)

[Clare~Bear]

Bond breaking needs an energy input - this is the easiest bit to start with and understand as it should be obvious.

Therefore, bond making gives out energy.

If more energy is given out (than is taken in if bonds in the reactants had to be broken, which doesn't apply to this) then the energy of the products is lower than that of the reactants, therefore it is exothermic.

It's the same whether the reactants are two compounds or an atom/ion and an electron. I think . . . I hope . . .

[LifeIsGood]

(Original post by charco)
A 'bond' is being formed between the electron and the nucleus. Bond formation leads to a more stable situation, so its an exothermic process.

Ok that's great, I thought there might have been another explanation for it and had to see if my prediction was correct.

(Original post by Enigma.)
Yeah so it's giving off energy so it matches whichever electron orbital its heading to occupy.

Imagine two cars are headed for a collision. One is positive and the other negative.

They crash. The crash gave off loads of energy (ie is exothermic) and the resultant situation is more stable (just a heap not moving at all)

That's a very good analogy, I don't think I will forget it after visualising a car crash

Thanks for the rapid responses!

Are there any trends within electron affinities? I'm not sure I need to know it but I'd like to know out of interest to deepen my understanding

[Clare~Bear]

(Original post by LifeIsGood)
Are there any trends within electron affinities? I'm not sure I need to know it but I'd like to know out of interest to deepen my understanding

First electron affinity down a group decreases. This is because the outer electron is further from the nucleus, plus you have an extra shell for the shielding effect each time you go down.

First electorn affinity across a period increases in general, I think it goes down slightly when an element has an electron in the next subshell to the last. With the nobel gas, it shoots right up, as you'd expect.

[Enigma.]

(Original post by LifeIsGood)
Ok that's great, I thought there might have been another explanation for it and had to see if my prediction was correct.



That's a very good analogy, I don't think I will forget it after visualising a car crash

Thanks for the rapid responses!

Are there any trends within electron affinities? I'm not sure I need to know it but I'd like to know out of interest to deepen my understanding

Cant remember. I left my Chem exam and 95% of it immediately vacated my head.