URGENT! Li and Cl URGENT!

[jazzoff]

Lithium and Chlorine both have valencies of one but they form positive one and negative one charged ions respectively during chemical reactions. Explain why. Pls reply ASAP!!!

[Aeternus]

You'll notice that Valency is the number of electrons an atom will happily recieve or give up -

 

http://en.wikipedia.org/wiki/Valency_%28chemistry%29

 

So Lithium and Chlorine both have a valency of 1 as Lithium gives up its 1 valence shell electron (2,1 electron shell config to simply 2), and Chlorine will take in 1 electron to fill its outer shell (basic understanding) (2,8,7 to 2,8,8). Lithium loses its electron becoming positive (+1), Chlorine gains an electron becoming negative (-1). Are you perhaps asking why this occurs??

[jazzoff]

Yes I am. So do you have the answer?

[Aeternus]

Its do with with the nucleus' effect (more specifically the protons) on the electrons at various distances from the nucleus and the diminishing of that effect due to shielding from other electrons. In Lithiums case there is an electron shell between the valence electrons and the nucleus (2 electrons in this shell) so we could say that there would be a +3 attractive charge towards the nucleus on that electron in the valence shell. However as we have this shell inbetween the effect of the charge from the nucleus is reduced, and we could say that there was perhaps only the equivalent of a +1 charge on this outer electron, meaning that it becomes much easier for this electron to be attracted towards other nuclei.

 

Chlorine has 2 shells totaling 10 electrons between the nucleus and the valence shell so we could say that the 17 protons resulting in roughly +17 unit charge would be reduced to roughly +7 (this isnt exactly the case and it is alot more complicated than I am making it out to be, there is shielding amount orbitals and therefore within each shell and the explanations are probably far more complex than I am making out) in the outer shell. So each of these valence electrons has this +7 charge pulling it towards the nucleus, a far stronger charge than lithiums valence electron had.

 

It is this difference in effective nuclear charge that means the difference in how it will lose its electrons or gain new electrons (chlorines large nucleus with few shells shielding means it can attract other electrons away from other atoms).

 

This can also be thought of in terms of energy required and energy gained from the loss of the electrons and the subsequent bonding formed, the fact that chlorines nucleus holds a greater sway on its electrons means it is much harder to pull an electron away from chlorine and so alot of reactions wouldnt be energetically feasible (although there are some reactions that involve chlorine losing electrons).

 

I'm sure someone far more qualified than me will come and correct me on numerous things or possibly even completely blow what I have said out of the water, but this is how things are explained as fair as I know at my level.

[akcapr]

isnt that just the same as electronegativity?

[NeonBlack]

I'm suprised that Aeternus actually gave you an answer. Aeternus, remember that URGENT!!! really means MY HOMEWORK IS DUE TOMORROW!!!

[jazzoff]

haha...it IS really due tomorrow, which is today. Thanks anyway!