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Topic: What's up with hydrogen?  (Read 3780 times)

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Offline mememehere

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What's up with hydrogen?
« on: November 21, 2009, 01:37:56 AM »
I am dubious abt hydrogen. I mean is it a metal or non metal? Also, why sometimes it can be positively charged hydrogen and sometimes negatively charged hydrogen?
eg: HCL and CH4??

Also, covalent is strictly for non-metals right? same goes for metallic bond, for metals only right? ???

Offline jcjlf

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Re: What's up with hydrogen?
« Reply #1 on: November 21, 2009, 04:06:28 AM »
It is a non-condusting gas at STP, so it can be considerd as a non-metal. Under high pressure (e.g. Jupiter's inner core) it may behave as a conducting solid, hypothetically.
In HCl and CH4 there is no ionic bond, therefore neiter H+ nor H- in these compounds. These are polar covalent bonds .
H+ is the same as a proton. It is the transferred particle in acid-base reactions, but it doesn't exist independently: it is always bonded to the electron-cloud of a molecule/ion/complex particle, e.g. H3O+ in acid aqueous solutions.
H- exists in solid metal hydrides, e.g. NaH, of group IA and IIA. These are ionic solids, react violently with water: NaH + H2O  :rarrow: NaOH + H2.

Indeed: covalent bonds (polar or non-polar) for non-metals and their compounds, metallic bonds in metals and their alloys :).

Offline cliverlong

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Re: What's up with hydrogen?
« Reply #2 on: November 21, 2009, 04:14:30 AM »
I am dubious abt hydrogen. I mean is it a metal or non metal?
Both and neither I would say. As always in chemistry the answer is more complex - and hopefully more interesting.
Why do you think many versions of the periodic table have hydrogen placed in the middle of the first period not assigned to any group?
It depends how you define a metal. Lattice of the nuclei with some delocalised electrons? Well, you can have metallic hydrogen if you want: http://en.wikipedia.org/wiki/Metallic_hydrogen

Can hydrogen be a Non-metal? Can form small covalently bonded molecules? Yes. Look at methane.
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Also, why sometimes it can be positively charged hydrogen and sometimes negatively charged hydrogen?
eg: HCl and CH4??
In both those cases the molecule is considered covalently bonded and hydrogen is not charged.
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Also, covalent is strictly for non-metals right?
I believe the distinction is not that clear cut. I have read that Aluminium chloride is covalently bonded
http://en.wikipedia.org/wiki/Aluminium_chloride
and that is a compound between a metal and a non-metal.
However, one can always look for exceptions and I think your generalisation is usually considered correct.
The problem is this as I understand. There aren't just ionic and covalent bonds with a wide gulf between them. Most chemical bonds (*) are about two electrons between two electrons with ionic being about the giving and receiving of electrons and covalent being about the sharing of electrons. However, the electrons can be "positioned" at any point between the atoms between those two extremes depending on the electro negativity difference between the atoms: http://www.chemguide.co.uk/atoms/bonding/electroneg.html#top


(*) see http://en.wikipedia.org/wiki/Three-center_four-electron_bond for exceptions
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same goes for metallic bond, for metals only right? ???
I think you can argue that the graphite allotrope form of carbon, with its lattice and delocalised electrons can be considered matallic. However, I think in almost all cases your generalisation is fine.

Offline mememehere

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Re: What's up with hydrogen?
« Reply #3 on: November 21, 2009, 11:08:02 PM »
so er... in conclusion?;)

Offline cliverlong

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Re: What's up with hydrogen?
« Reply #4 on: November 22, 2009, 05:37:37 AM »
so er... in conclusion?;)
So , errr ... are you looking for a definitive yes / no to your question?

Well as I think I argued in my post it doesn't work that way, but that most of the time your generalisations are adequate  -except for your error about HCl and CH4.

Clive

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