Soo, I am suppose to write an essay about comparing the electron affinity of potassium and lithium... I know that both of these elements do not usually form a negative ion and that they're part of the same group. So now I'm stuck because I have nothing to talk about. Any thoughts or ideas on what I should write?

That's very true, they do form positive ions. However, they do still have a certain degree of electron affinity, albeit small. Are you comfortable with the concept of electronegativity and the trends seen in the periodic table?

Yeah, I'm familiar with the trends in the periodic table and somewhat touched on electronegativity. However, the problem is that I have to write at least two pages about the two elements. All I can think of to write about is their atomic radius, valence electron and their tendency to form positive ions instead of negative...

Well you could also talk about their reactivities as per the reactivity series. This could easily be discussed in terms of how well potassium is able to lose an electron over lithium, etc.

 

Additionally, you will want to discuss electronegativity - i.e. which one is more electronegative and why that is.

Ohhh! I totally forgot about the reactivity series. I think I have enough to write a decent essay about it I guess. Thanks for you help!! I really appreciate it =]

Well I'm a bit late as it seems you've already got the hang of it...anyway I was going to suggest that you talk about the trend in reaction enthalpies [imath] \Delta H [/imath] of group I metals and their reaction with water. The reaction gets more exothermic down the series, so all other things held constant this is reasonable measure of the group I metals tendency to lose an electron as the reaction is essentially [ce]M \rightarrow M^{+} + e^{-} [/ce]. This might give your essay a competitive edge on those of your classmates .

 

This is basically an equivalent argument to the electrochemical reactivity series mentioned by hypervalent_iodine but in terms of thermo. It's always nice to see it from a different angles I guess.