Is carbon and graphite the same thing

The electrical conductivity Why is a substance electrically conductive?

A substance is electrically conductive because it contains freely moving charged particles.

On this page you can learn more about
  • the conductivity of metals
  • the conductivity of graphite
  • the conductivity of salts and other ionic compounds
  • the unit of conductivity
  • Conductivity in numbers
The conductivity of metals

Why do metals conduct electricity? If atoms only have 1, 2 or 3 valence electrons, neither ion nor atom bonds can form between 2 atoms of this element. Ionic bonds cannot develop because one atom would have to give up its valence electrons (this works fine with 1 - 3 valence electrons) and the other atom would have to take up these valence electrons in order to form a noble gas configuration with its own valence electrons. This is not possible; there are not enough electrons.

Atomic bonds cannot form because 2 atoms use their valence electrons together to fill the valence shell with 8 electrons. There aren't enough electrons for that either.

So the metal bond is formed. With it, all valence electrons are freely movable in the entire crystal, they are, so to speak, shared by all atoms. This state is called "electron gas", although it has nothing to do with the gaseous state of matter.

What happens with the power line in metals? When a voltage is applied, the electrons slowly migrate through the crystal (and of course through other metallic objects such as copper wires).

The most important properties of metallic conductors

  • The power line does not cause the conductor to decompose
  • The conductor has a negative temperature coefficient, i.e. when the temperature increases, the electrical conductivity decreases.

Why do some metals conduct electricity better than others? This question can be answered with the band model derived from quantum mechanics - not on my website.

The conductivity of graphite

Why does graphite conduct electricity?

The graphite crystal is made up of layers. Each layer consists of an infinite number of six-membered rings made of carbon atoms. Each carbon atom uses 3 of its valence electrons to form bonds with the neighboring atoms. The remaining, "fourth" valence electrons form a system of delocalized molecular orbitals, which means that they can move freely in the entire layer, and current conduction takes place.

Graphite therefore only conducts the electrical current within the layers. It is an insulator perpendicular to the layers. This phenomenon is called anisotropy.

In commercially available graphite, a great number of tiny crystals are randomly arranged so that layers of individual crystals that are tilted against each other touch each other. Power is conducted in all directions.

The conductivity of salts and other ionic compounds

Why do ionic compounds conduct electricity? Ionic compounds (for example salts, acids, oxides and hydroxides) are substances that can dissociate into ions. Positively charged ions are called cations, negatively charged hot anions.

in the solid state Ionic compounds form crystals. In these crystals, the ions are not free to move, but are located in a crystal lattice in fixed places. So there can be no current flow.

in the liquid (molten) state the ions can move freely. If a voltage is applied, the cations migrate to the cathode, the anions to the anode and discharge there. Electricity flows. The same thing happens in the dissolved state.

What happens when current flows in ionic compounds? When a voltage is applied, the ions migrate: cations to the cathode, anions to the anode.

The most important properties of ion conductors are

  • When a current flows, the ionic compound decomposes. As soon as all ions have migrated to one of the electrodes, there are no more freely moving ions (of course!) And no more current flows.
  • Ionic conductors have a positive temperature coefficient, i.e. when the temperature increases, the electrical conductivity increases. The reason is the decreasing viscosity of the water. The conductivity only decreases again at high temperatures.

Why do metals conduct electricity better than ionic compounds? The charge carriers in metals are electrons, in ion conductors they are ions. Ions are much larger than electrons and therefore much less mobile.

Examples of ion conductors: sodium chloride

The unit of conductivity

The unit of conductivity (also called conductance) is Siemens, abbreviation S. The following applies for the conversion: 1 S = 1 A / V = ​​1 / Ohm.

The conductivity is the reciprocal of the resistance.

The conductivity L depends on the length l and the cross-sectional area q of the conductor through which it flows, and of course also on the material from which the conductor is made. The following applies:

Here is κ (kappa) the specific conductivity. It is different for each substance and depends on the temperature and, in the case of solutions, also on the concentration. The unit of the specific conductivity κ is 1 / ohm * cm.

How big is the conductivity?

The conductivity of different substances is very different. It extends over many powers of ten. The graphic only gives an approximate overview of the order of magnitude of the conductivities of individual substance classes.