Why carbon has very low resistivity while coal or hydrocarbon have high resistivity?

Answer 1

High resistivity is the inverse of conductivity, and Carbon is not a good conductor (although it could be a better conductor than most hydrocarbons). Here are a few examples:

Carbon - 0.07 x 106 S cm-1 (not a good conductor)

Silicon - 1.2 x 10-5 S cm-1 (not a good conductor - used for this purpose in microchips)

Copper - 59.6 × 106 S cm-1 (good conductor)

Atoms in metals (good conductors) are held together by bonds between nuclei and their electrons. Atoms in nonmetals (bad conductors) are held together due to the atmos' sharing of valence electrons (ie covalent bonds).

Conductivity has to do with how easily electrons can move. In metals, electrons are more free to move than nonmetals, resulting in better conductivity. Silver is the best conductor, I believe. Sorry for the run around, but the basic answer to your question is this: I suspect in hydrocarbons, the valence electrons are more restricted due to the covalent bonding to the hydrogen atoms.

Answer 2

Carbon in its pure form has a crystal lattice structure that allows for the easy flow of electrons, resulting in low resistivity. On the other hand, coal or hydrocarbons have impurities and irregular structures that hinder the flow of electrons, leading to higher resistivity.