What constitutes a metal?

[R1Geezer]

In the periodic table there are lots of metals, great, often there names end in "ium". Can anyone explain to an element novice what properties does an atom have to have to be considered a metal? I mean some metals are obviously so eg iron, others eg sodium do not give the appearance of a metal but are classified as such. Thanks

[Robb Phoenix]

Any material with high Malleability, Conductivity, Ductility,Luster.
Mainly they must have relatively free valence electrons to enable conduction (both heat and electricity).

[nightmare]

R1Geezer
sodium - shiny, silver metallic appearance. Looks pretty much like a metal to me. Admittedly, you do not often see the surface of a piece of sodium, at least not for long.What you usually see is the reaction products of sodium's exposure to air.