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Reactivity up and down a group
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chemistrysubjec...
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Joined: 10/06/2007 - 22:31
Posts: 347
Reactivity up and down a group
chemistrysubjec...
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Joined: 10/06/2007 - 22:31
Posts: 347
Reactivity up and down a group

I was asked this question:

Why do the reactivity of the group 1 atoms increase as you go down the group, but the reactivity of group 7 decreases as you go down the group. I get why it does in group 1, but I don't get why it does in group 7??

The answer lies in understanding what the atoms are trying to do. Group I metals are aiming to lose an electron from their outside shell. This can happen easiest if the electron is in a shell that is a long ay from the nucleus so that there is less attraction between the nucleus and the electron. The biggest atoms are at the bottom of the group so they are the most reactive.

The halogens react by gaining an electron to form the halide ion (eg chlorine becomes chloride). This extra electron is held tightest when it is placed in a shell close to the nucleus. This is best when the atom is as small as possible and so fluorine is the most reactive of the halogens.

Break the idea down into clar statements:

Attraction between nucleus and electron is greatest for small atoms.

The small atoms are at the top of the groups.

Group I metals want to lose an electron while halogen atoms want to gain an electron.

So, large group I metal atoms are the most reactive and large halogens are the least reactive.

Hope this helps.

ife88
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Joined: 17/02/2009 - 16:40
Posts: 22

Thank you :) I understsnd it now.

chemistrysubjec...
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Joined: 10/06/2007 - 22:31
Posts: 347

Good. Ready for the next one whenever. It is a good idea to start a new thread for the next question so that the range of discussions can be seen by anyone browsing through.