#1
iis fairly basic chemistry , i have got a copy of the test im oding tomoro.... dont ask how i got it, but there are two questions i dont under stand, can any body help???


in terms of structure and bonding, explain
A) why the electrical conductivity of sterlinf silver (an alloy) would be expected to be lower than that of pure silver?

B) why silver has a higher melting point that sodium
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#2
Quote by new_kirk_hammet
iis fairly basic chemistry , i have got a copy of the test im oding tomoro.... dont ask how i got it, but there are two questions i dont under stand, can any body help???


in terms of structure and bonding, explain
A) why the electrical conductivity of sterlinf silver (an alloy) would be expected to be lower than that of pure silver?

B) why silver has a higher melting point that sodium



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#3
A) because the different sized atoms in the silver alloy create electron resistance throughout the sea of electrons.

B) Because silver is less reactive than sodium.

hope that helps.
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#4
does the melting point of silver compaired to sodium have anything to do with silver needing more energy to melt it?
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#6
yes, its to do with the energy needed to remove the bonding between silver atoms.

I'm not sure here, but i believe thats called Van'der whals force. or something like that, which holds elements together.

note* not in ice though, thats hydrogen bonding.
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#7
Silver "resists" the energy(=heat) better than sodium, hence the higher melting point.
#8
Quote by new_kirk_hammet
does the melting point of silver compaired to sodium have anything to do with silver needing more energy to melt it?

well the more energy something has the more reactive it is. like sugar mets quicker than bran flakes.
#9
For the melting point one, silver will have a higher melting point because the energy holding the atoms together in a lattice is larger for silver than for sodium. Therefore, you need to put more energy into it (heating) in order to give the atoms enough energy to separate and go into the liquid phase.

As for the conductivity one, I'm not entirely sure, I'm not a physical chemist, so not my specialty.

Edit: may have phrased that badly.

Basically, you need to put energy into a bond to break it. You need to put more energy into bonds between silver atoms to break them than for sodium ones.

Also, it has absolutely nothing to do with the reactivity in this case. When you melt it, it's not reacting with anything.
Last edited by AtomicFire at Apr 20, 2008,
#10
A) Silver being a metal would normally have a large amount of delocalised electrons allowing easy flow of charge through the metal. But the alloy distrupts this system resulting in less delocalised electrons, therefore it will transfer charge slower.

B)Because the a silver atom has more electrons than that of sodium and so its vandarwells (sp?) bonds and stronger.. Therefore more energy is need to seperate the silver atoms.

Thats what my answer would've been. But then again ive done Alevel chemistry.
#11
In answer to B), the intermolecular forces in the silver atoms are stronger than in sodium and require more energy for the forces to be overcome, so it has a higher melting point than sodium.
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#12
Van der Waals is how it's spelt people.

yeah ok, ya got me.
Last edited by ooder the cow at Apr 20, 2008,
#13
It is due to the fact that all of the electrons leave the atoms and 'float' around in a 'sea'. The atoms are then ions and are all attracted to the negative sea of electrons, this then causes them to stick together.

The reason silver would have a higher melting point is because each sodium atom will only give 1 electron to the 'sea' and this would cause all of the ions to be less attracted to the sea. Silver on the other hand has a larger number of electrons in its outer shell, which would be donated to the sea, this causes the sea to be more strongly charged, and the ions to be more strongly charged, this would cause them to stick together more.

Goddam I love chemistry.
Last edited by blynd_snyper at Apr 20, 2008,
#14
thanks alot people
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#16
Van der Waals forces wouldn't apply to this case, as they are induced dipole moments between molecules. Metals are held in lattices, as AtomicFire said. He pretty much covered the entire answer.

For conductivity, my guess is that silver, being a d orbital element, has loads of electrons holding the lattice structure together, which can carry charge.
#18
I dunno why the hell people are talking about Van der Waal's Forces, seeing as they are bonded by metallic bonds, not temporary dipoles.

Blynd snyper explained why the metallic bonds in silver are stringer in silver than sodium very well.
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#19
Yeah, just to help clear it up TS, Van der Waals' forces occur when a molecule's electrons all move to one side at the same time, this then causes a temporary dipole (one side being positive, the other being negative) which causes other molecules to be attracted to one side of it, this has nothing to do with the questions you are asking about and if you claim it is you may lose marks.
#21
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yes, its to do with the energy needed to remove the bonding between silver atoms.

I'm not sure here, but i believe thats called Van der Waal's forces. or something like that, which holds elements together.

note* not in ice though, thats hydrogen bonding.

fixed (close enough though) EDIT: beat to it

Silver is denser than sodium so there is more attraction between the nucleus of a silver atom and its electrons, and it takes a lot more energy to change stronger bonds than weaker bonds. (something similar to electronegativity and things like that)
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#22
Lol, some people are getting really confused here.

1. Not Van der Waals forces. Metallic 'sea of electron' bonding, as previously explained very well by blynd snyper.

2. This has absolutely nothing to do with reactivity. It's melting, not reacting. Besides, reactivity is a horrifically vague term. Sodium may well be more reactive than silver with water or oxygen etc. because it is more electropositive, however this is not always the case with everything.

3. Doesn't really have anything specific to do with density either, as density is a bulk property. Density may well be a consequence of the bonding, but I wouldn't like to say that without a reference.

As for the conductivity, I was thinking about it and I think maybe because the silver atoms all have outer bonding (d) orbitals of similar energy that they can overlap more easily to form the conductive electron 'sea' which is actually more like a band of degenerate orbitals. If you stick an atom with a different energy bonding orbitals in there, the overlap would be less and therefore electrons would not transfer as easily.

Have to say that that's just my reasoning, and I can't say for sure if it's correct. Also it's a bit more detail than you'd need for GCSE or A-level methinks.