Re: Does hydrogen count as a metal?

Hydrogen does not count as a metal; it is clearly not metallic.

A term like 'metal' is really a classification of convenience, rather than 
one that is laid down by strict laws of nature. 

The term 'metal' is usually used to refer to a group of physical properties 
that a material has. The main one is a high electrical conductivity, where 
the electric current is actually conveyed by 'free' electrons within the 
metal structure; other important properties that form part of the picture 
is that metals are opaque and lustrous and good thermal conductors. And, if 
they are solid rather than liquid, metals exhibit some plasticity -- they 
can be beaten out into thin sheets, or drawn into wires. 

Not all metals exhibit all of these properties: a few are very hard and 
brittle, for example, and show little plasticity. It is the overall picture 
that counts.

We could call this the 'physical concept' of a metal. There is a quite 
distinct 'chemical concept' of a metal or, more precisely, a metallic 
element. In this chemical sense, a metallic element is one near the left 
hand side of the periodic table, that takes part in chemical reactions 
where it loses electrons to form positive ions, particularly in aqueous 
solution, or in salt crystals. 

If we take a metallic element (in the chemical sense), we find that, as a 
simple substance the material is a metal (in the physical sense). Copper, 
calcium, and mercury, for example, all show the set of physical properties 
that would lead us to call them metals. And they all enter into chemical 
reactions where they are transformed to positive ions in aqueous solution, 
or where they are in crystalline salts as the positive ionic part.

But there is an important difference between the two ideas. There are 
plenty of compound or complex substances that we would still call metals in 
the physical sense: alloys or amalgams where more than one element is 
present. Usually they are all metallic elements, but sometimes a non-
metallic element can get in on the act. Brass, bronze, pewter, solder, and 
the like are all metals. It would also be true to say that, in the physical 
sense, only solids and liquids can be metallic; the vapours of mercury, 
calcium and copper show none of the characteristic physical properties of 
metals. Tin is a borderline element that is usually regarded as metallic in 
the chemical sense. It comes in two physical forms. One of them is the 
familiar form of tin that is used as a surface coating; it is clearly 
metallic. There is also a non-metallic form of tin that shows none of the 
characteristic physical properties of metals.

What about hydrogen, then? In the physical sense, hydrogen is a gas. Even 
if we chill it to extremely low temperatures, it forms a colourless liquid, 
and ice-like transparent crystals of solid. It is not metallic. There is a 
prominent view that it might be possible to form a metallic form of 
hydrogen at low temperatures and extremely high pressures, and a claim that 
it has been done. Check out
 
metallic hydrogen factsheet 

The conditions on Jupiter are such that metallic hydrogen might be present. 
Have a look at

 Jupiter question   

In the chemical sense, hydrogen is regarded as a non-metallic element, in 
spite of its position on the periodic table. Hydrogen does occur as 
positive ions in aqueous solutions, but not in crystalline salts. Hydrogen 
chlorine is a gas, for example, where sodium chloride or copper chloride 
are crystalline salts. The bond in hydrogen chloride is polar covalent, not 
ionic.