Difference of Electron storage in metalloids and metals

[hubewa]

Metalloids such as silicon share similar properties to metals, yet the way that electrons are held in both materials are completely different.

Whereas the electrons from silicon atoms are orbiting the nucleus, the outer shell of the electrons of metallic atoms are "stripped" from the atom and, as a result, form a sea of electrons.

Why is there such a difference between metalloids and metals?

 

[ardie]

without knowledge of quantum mechanics, intuintivaly it can be thought of as this: the metals have F orbitals, which is a low energy orbital. i.e. the electrons in this orbital easily get knocked off by the atom colliding with others... (in very simple terms). the metalloids like sillicon have partially filled F subshells which makes them a semi attractive host for free electrons. However conductive metals like copper have an almost filled subshell which makes them ultra attractive for free electrons. (bearing in mind the further you fill up the subshell, the less energy the electrons need to fill up the remaining slots)

 

[hubewa]

Fine, but why don't heavier non-metal atoms share the same properties as semi-conductors where they have a partially filled F orbital that allows it to conduct electricity?

 

[ardie]

once you understood the idea behind the electrons of F orbitals, you can model the electrons flowing as a gas of fermions without much agitation due to the surrounding atoms. intuitively (maybe even wrong but just a case that makes it easier to imagine) the electrons comprise a set of wavelike functions that travel across the whole of the metal. in a semi conductor, by introducing a wall like object (a single atom with a fully filled orbital) the sea of flow of electrons can be controlled such that electrons arent allowed to pass through the doped atom in the lattice. so you have a wall type objects in your conductor that only allows electrons of certain energies through.

 

[IttyBittyBit]

'Metalloid' is an imprecise term without any definite agreement on what it means. See: http://en.wikipedia.org/wiki/Metalloid#1960.E2.80.93

'Semimetal' on the other hand, is a term with a precise definition. Recall that the ease of which a material conducts electricity is correlated with how many charge carriers it has. Metals have lots of charge carriers since their electrons are free to move around. Semiconductors normally don't have free electrons, but a small electric field (or dopant atoms) can liberate enough electrons to carry current. Semimetals are somewhat 'strange' since, unlike metals, electrons need to be freed from atoms, but unlike most semiconductors, just the thermal energy of the material is enough to do this. (A more accurate way of saying this would be to say that they have negative indirect band-gap). Therefore they are less conductive than metals but somewhat more conductive than semiconductors.

 

[hubewa]

Sorry for the long reply.

Correct me if I'm wrong but, from what I understand, it seems like semi-metals have a bonding structure which is closer to non-metals than metals (ie, it is like a covalent bond) except that they have a special property where you can liberate enough electrons to carry current due to the low thermal energy of the material.

In this case, though, what's the difference between a semi-conductor and a semi-metal? Would a semi-conductor include materials like graphite and semi-metals materials like silicon?

 

[ardie]

ok maybe read my post again. semi conductors have imaginary walls in them whereby electrons need some energy to pass through, so they are good conductors given some energy is provided. semi metals do not have walls they are just harder to liberate electrons in at all, hence bad conductors no matter what energy we give them.

 

[hubewa]

Oh okay. I understand it now. Thanks for posting and helping.