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Author Topic: Why are Group I metals more reactive towards the bottom of the periodic table?  (Read 11806 times)

Offline Poetic-Justice

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Hello,

Im interested in why as you go down the group I metals, they become more reactive?

Im a bit confused, as my notes from class say that as the metals lose electrons to gain a full outer shell, the further away from the nucleas the electrons are, the more reactive the reaction is. I would have thought that as the electron(s) is further away from the nucleas, the electron can leave easier as the protons are further away. And surely with it being easier to leave, there should be a less reactive reaction?

Anyone have an answer? I would ask my teacher, but we've just started the holidays, and I cant afford not to revise well at the moment.

Thanks anyway,
Poetic-Justice
« Last Edit: 26/05/2008 10:17:21 by chris »


 

Offline StereoChemist

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The fact that it is easier for the electron to leav makes it more reactive, in the smaller G1 metals the electrons are more tightly held and are not lost as easily this makes them LESS reactive because the reaction involves loss of the electron.

another way to think about is the energies of the electrons, generally higher energy electrons are more reactive beacause things generally react to lower themselves in energy.  and it is easier for a high E electron to get to lower E state than a low E electron to go even lower.  The valence electrons in the large group 1 metals' orbitals are in higher energy orbitals because they are in an orbital with a higher quantum # n.   a good fact to know is that (there are always exceptions in chemistry though) electrons that are closer to a nucleus or on a more electronegative atom are lower in energy.  So on the reacting species that is being oxidized it is always preferable for the leaving electron to be in a high energy (high n) oribtal.
 

Offline Supercryptid

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Take note of these heats of formation:

LiF = -616.93 kJ/mol
NaF = -575.38 kJ/mol
KF = -568.61 kJ/mol
RbF = I couldn't find it.
CsF = -554.67 kJ/mol

These are the products generated from reactions of the Alkali Metals with fluorine, which give rise to the corresponding fluoride salts in the solid state. The negative sign means that the reaction that creates these salts releases energy. Notice that the energy given off by the reactions actually goes down as you go down the Alkali Metal column.

I think the reason why, say, cesium reacts more readily with something like water than lithium does despite this decrease in reaction energy is because of its lower melting point. As heat is generated by the reaction, it melts the cesium faster than it does for lithium. Once it's in a liquid state, the metal has an increased surface area to which the water can react.

The metals do get ionized more easily as you go down the column, though, as pointed out above.
 

Offline Poetic-Justice

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Thank you ever so much, especially StereoChemist. Thank you again!
 

lyner

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A simpler, 'school level' explanation is that, as you go down the periodic table, there are more inner shells which can be looked upon as screening the single outer electron from the attraction of the single net positive charge inside their orbit. The effect is more marked for Group 1 elements.
 

Offline Poetic-Justice

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Ah, ok. Thanks!
 

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