What defines an element as a metal?

Definition: substance with high electrical conductivity, luster, and malleability, which readily loses electrons to form positive ions (cations). Metals are otherwise defined according to their position on the Periodic Table, including groupings as alkali metals, alkaline earth metals, transition metals, and rare earth metals.
Eric R Snow wrote:

I read as much as I could find but still haven't found something really specific. It seems like there opinions about some elements as to whether thay are truly metals. ERS

It's a combination of factors, mainly electron mobility (causing conductivity and subsequent reflectivity) and a metallic lattice (although the crystal systems - BCC for example - are about the same, I seem to remember there's something different relating to the spare electrons). Crystal deformation, i.e. malleability is also a typical feature.
Some other elements and compounds posess conductivity, graphite for example, many sulfides (pyrite, galena, etc.) and oxides (cuprous oxide, lead dioxide, etc.) and so on (gallium arsenide for example is used for LEDs and as such must have free charge carriers). But none of these are classified as metals for reasons of luster and malleability.
Some metals, for example tungsten, uranium (IIRC) and bismuth (in my experience) are on the brittle side (in the case of tungsten however, it is merely below the brittle-ductile transition, something iron experiences particularly with high sulfur impurity), but still win out as metals by appearance, behavior in general, and of course geography on the table.
Then there's the semimetals, such as silicon, arsenic, selenium and tellurium. They have a metallic appearance, but tend to act as nonmetals, forming cations most often. So being on the fence, they are merely classified as such!
Tim
-- "California is the breakfast state: fruits, nuts and flakes." Website:

Germanium? You're not going to ignore germanium, are you? That's my favorite.
R, Tom Q.

The main defining feature is that the atoms form metallic bonds with each other. (How's that for circular?!) Really, though, metallic bonds are when each atom readily gives up its outer shell of electrons (aka, the valence electrons). These electrons form a "sea" which surrounds the atom cores (cations). The atom cores and the sea are oppositely charged, so they are mutually attracted to each other --> bonding.
It's this particular kind of bonding that accounts for the usual properties of metals. Metals are (usually) ductile because the bonds are vague and non-directional; thus atoms can slide by each other without completely *breaking* a bond (ductility is complex and requires "dislocations", but that's the gist at the dislocation itself). Metals conduct electricity and heat bc all those free electrons really are free to move about. Melting temp and modulus of elasticity (stiffness) are directly related to how strong the bonding is--big clunky atoms like gold and lead have weak bonds. Strength has more to do w/ macroscopic things like grain boundaries, crystal structure, and impurities (e.g., carbon in steel, which prevents the iron atoms from sliding past each other so easily -- that's why steel's ductility is inversely proportional to it's strength. Pure iron is soft like lead.)
Here are some nice pics and explanations: David Malicky

As well with my Aunt; she has a garden full of them. ;)
Jon

On Wed, 15 Jun 2005 00:15:10 -0700, the opaque "Jon Danniken" spake:
I must be in central Europe. ;)
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Thanks for the links David. It seems that nothing is simple. But that's what makes life interesting. Eric