physics

[BAT7722]

what are free electrons in any material? Is a metal constituted of free electrons or a crystal?

which one is better off as a conductor, a metal or crystal?

[Gef]

Free electrons are electrons which are not bound permanently to atoms and can move throughout the substance.

Not many classes of substance have free (or delocalised/mobile) electrons. Metals and graphite have mobile electrons and that is why they are good conductors of electricity.

I am not a metallurgist but I know that many metals have crystalline structures and conduct. However, ionic compounds have crystalline structures in the solid state and they do dot conduct since they do not have free electrons.

[TeeGee]

When a potential difference ( voltage ) exists along a substance, free electrons near one end of the substance are attracted to one end of it. This leaves depleated atoms which in turn attract free electrons from their neighbours, and so on. A good conductor is a substance that allows the rapid release and replacement of electrons. An insulator, on the other, hand strongly resists such movement. Metals ( some crystaline ), some crystals and other substances ( water for example ) allow the release of electrons and as such are deemed to be conductors.
In the manufacture of crystals, they can be 'doped' and have a surplus of electrons ( n-type ) or a depletion ( p-type ). Joining a p-type crystal to an n-type crystal give you a simple diode, which allows electrons ( conduction ) one-way only. Does that help?

[Gef]

TeeGee's answer gives a good description of semiconductors but contains at least one glaring error. Water, to all intents and purposes, is a non-conductor of electricity. To detect a current flowing in water you would need very, very, sensitive equipment and even then the tiny, tiny current is carried by ions and not electrons.

[TeeGee]

Thank you for your accolade gef, but I beg to differ - quote - When one or more electrons are torn off an atom, the remaining atom becomes positively charged and is known as a positive ion - unquote - in other words a 'hole' into which electrons can slip, and it 'travels' in the oppostite direction to electrons being a depleted atom.

[Gef]

TeeGee I agree entirely with your last answer but you won't find any free electrons in water.