How Does A Substance Come To Be Classified As A Metal?

[sandyRoe]

On a tv quiz this afternoon calcium was included in a short list of metals. I wouldn't have thought it was.

[Canary42]

Me neither.

[Mamyalynne]

Basics here if you fancy a read, bit I know what you mean.


https://en.wikipedia.org/wiki/Metal

[Mamyalynne]

^ but

[Mamyalynne]

This is perhaps more succinct.


http://www.britannica.com/science/metal-chemistry

[Baldric]

///Calcium is a chemical element with symbol Ca and atomic number 20. Calcium is a soft gray alkaline earth metal, fifth-most-abundant element by mass in the Earth's crust.///

[ToraToraTora]

Yes, I too have often been confused by this, Sodium/Calcium are well known as metals but the properties that constitute a metal have been poorly defined as far as I can see. It gets even worse when, for example you hear that the pressure at the centre of Jupiter means that Helium exists in a metallic form! So I imagine that a metal can be a state of existence too, I also am confused, let's hope a bright chemist comes along soon to help.

[SSSid]

Interesting question!
Googled this:-
http://www.elementalmatter.info/list-of-metals.htm
I would never have thought of calcium as a metal.

[EDDIE51]

Chemical definition of a 'Metal' here.
http://www.chemicool.com/definition/metals.html
Calcium is definitely a 'metal'.

[jomifl]

If you saw some calcium you would have little doubt that it is a metal, just like potassiun and sodium.

[EDDIE51]

Calcium, Sodium and Potassium are rarely seen in elemental form, they are too reactive. They have to be stored under oil in a laboratory as they react with moisture in the air and form Hydroxides.

[jomifl]

You are correct Eddie but they don't just vanish when taken out of the oil. In air they slowly react with the oxygen, CO2 and water present but not so quickly that they don't look like metals.

[EDDIE51]

I started work in a chemistry lab back in 1968. In those days we dried solvents by putting Sodium into the bottles. The Sodium was bright and shiny but only for a minute or less. We used a Sodium press to extrude it into the bottles. Health and safety hardly existed then!!

[sandyRoe]

I suppose my question was prompted by ignorance as much as anything. I'd always thought of metals as iron, copper, lead and the like.

[beso]

You only normally come across the alkali metals as salts or oxides because they are so reactive. You probably would not think of Iron Oxide or Copper Sulphate as made of metals either.

Aside for the propensity to react an important difference with the familiar metals is the size of the oxide. When a metal reacts with oxygen the oxide crystal can be bigger, smaller or similar size to the metal structure.

If it is bigger then the material swells up and the oxide flakes off as we see in severely rusting iron. If it is smaller (the case with many alkali metals) then the material develops holes which open more material to reactions.

Materials whose oxides are similar in size to the base metal form a tight surface that does not react further. Such is the case with aluminium where the surface is coats with a thin layer of oxide (in essence, Sapphire) preventing further reactions.

[Ianfiat]

The O level definition was metals form basic oxides/(hydroxides) whereas non metals form acidic oxides.
A better definition is that metals tend to form positive ions and non metals negative ions.

[Peter Pedant]

what is wrong with the defn ( O level )
that Group I and II elements are definitely metals ?

calcium - definitely metal

thing about Al and Hg - which usually look like metals - is that they can covalently bond ( V un-metallic ) and Sandy if you have a long memory, it was the oily AlCl3 which poisoned all the people at Camelford - whilst people who really should know better were saying stop panicking Al is ionic and has low solubility

[gumboot]

Sorry to be pedantic Peter Pedant but it was aluminum sulphate that caused the poisoning at Camelford rather than aluminium chloride, which is the compound you provided the formula for. Nevertheless, I'm at a loss to understand what "oily alCl3" is supposed to be as even if it was alCL3 that was delivered to the site, it is not "oily" in any sense. Just like aluminium sulphate, aluminium chloride is soluble in water.

Aluminium sulphate does indeed have a good solubility amounting to around 35g per 100ml of water at the temperature likely in the holding tanks at Camelford. However, I'd point out that Al is indeed ionic and low solubility not least because the chemical symbol Al refers to the pure metal aluminium rather than one of its compounds - aluminium can be regarded as insoluble in water as we all know.

[EDDIE51]

^^ yes it was Aluminium Sulphate which is used to treat drinking water.
The mistake was to accidently put in far too much, it should have been a max of 20 ppm (parts per million) 0.000002% , they put in over a 1,000x too much!

[Peter Pedant]

oops thanks for that !

oily - why did I think the aluminium at Camelford was covalent ?
because it came in a tanker ?

because they said at the time the solubility product for ionic aluminium was far too low ( to do damage ) ? anyway thanks for that

( Read the Enemy of the People by Ibsen. The GP who alone says these people have been seriously poisoned ....... gets kicked out ! )

[Hypognosis]

Interesting thread. It's not possible to forget more than you ever learned about a thing but it certainly feels like it, with this crowd ^^^. Ta.

I did happen to find this little nugget, while digging

//Douglas Cross, a consultant biologist based in Camelford, tested the water and found that it contained "not only aluminium sulphate but other noxious substances, too. As the acidic liquid travelled from the plant into people's homes, it corroded the copper pipes and their soldered joints, made of zinc and lead."[1][14] Official advice to boil the water before drinking was, according to Cross, "dangerous advice because it concentrates the contaminants.//