Can burn graphite

graphite

structure

Graphite is a modification (appearance) of the element carbon, which occurs naturally alongside diamond, another carbon modification.

Graphite crystallizes in a so-called layer structure. Within each layer the carbon atoms are too Hexagons arranged - similar to honeycomb. Each carbon atom is covalently linked to three other carbon atoms. However, the individual layers are not exactly on top of each other; The first layer, the third, the fifth and so on are congruent, correspondingly the second, the fourth, the sixth and so on.

Explanation for the lower secondary level and the levels EF and Q1:

For these covalent bonds three of the four outer electrons of the carbon atom are "consumed". The fourth outer electron is not involved in these bonds. These electrons "buzz" around as free electrons between the carbon atoms within the graphite layer and can be easily shifted by applied electrical voltages. This explains the high electrical conductivity of graphite. Often these free electrons are also referred to as electron gas because of their behavior.

There are only weak van der Waals forces between the layers, which is why the layers can easily be shifted against each other, which is useful in everyday life, for example when writing with a pencil. Incidentally, the name "graphite" comes from this, the Greek "graphein" means "to write".

One of the many layers of the graphite crystal, shown in perspective. The "fourth" electrons are shown in blue and blurred because they can move within the layer. Author: Ulrich Helmich

Explanations for level Q2 and beyond

All carbon atoms in graphite are in sp2hybridized form. The pz-Orbitals of the carbon atoms within a graphite layer therefore overlap, and an electron gas is formed - similar to a metal - that can be moved very easily in an electric field. Hence, graphite is righthigh electrical conductivitybecause all electrons of the pz-Orbitals are delocalized over the entire graphite layer.

A single layer of graphite with the pz-Orbitals. Author: Ulrich Helmich

The pz-Orbitals of the graphite layers lying on top of one another, on the other hand, only overlap very weakly.

The C-C distance within a layer is 246 μm, while the distance between two congruent layers is 670 nm. Therefore, the chemical bond between the layers is not particularly strong; basically only van der Waals forces prevail between the layers. The graphite layers can therefore easily be shifted against one another.

Three layers of a graphite crystal. The layers are offset from one another according to the A-B-A-B pattern.
Source: engl. Wikipedia, Author: Benjah-bmm27
This work has been released into thepublic domain by its author,Benjah-bmm27. This applies worldwide.

properties

Graphite is a gray-black to black, very soft non-metal, but partially shine metallic can. Its density in its purest state is 2.265 [1], in the "normal state" the density is between 2.1 and 2.3.

Usually when you think of graphite you think of carbon. However, in contrast to coal, graphite is even not so easily flammable [1]. Graphite does not have a melting point, but it sublimes at about 3750ºC [1].

A very distinctive feature of graphite is its low hardness. It feels soft and greasy to the touch [1]. Graphite can therefore also be used as a lubricant in industry.

Graphite is characterized by a high light absorption off, so it usually appears black. The cause of this high absorption are the free electrons, which can very easily be raised to a higher energy level.

Because the carbon atoms are very firmly connected to each other by covalent bonds, graphics are in almost all solvents insoluble, both organic and inorganic.

use

At school, graphite is mainly used as an electrode material for electrolysis. In industry, graphite is used as a lubricant and as an electrode material for electric arc furnaces, but also for melt flow electrolysis in metal production [1].

Wikipedia [2] lists a whole range of possible uses for graphite, only a few of which are to be mentioned here:

  • Pencil leads
  • Solid lubricant
  • Casting molds (lining)
  • Furnace linings
  • Electrodes for metal fabrication

Natural forms of graphite

The natural forms of graphite are coke, soot, and charcoal [3]. All three forms consist of contaminated graphite.

soot is a black powdery material that is often produced when organic compounds are burned, especially when they contain a high percentage of carbon. Benzene and toluene, for example, burn with a very sooty flame, while ethanol burns with a blue flame and hardly produces any soot.

The carbon content of benzene can be derived from the empirical formula C6H6 easy to calculate. The molar mass is 78 g / mol, the carbon has a share of 72 g / mol, that is 92%. Ethanol with the empirical formula C2H5OH has a molar mass of 46 g / mol, but the proportion of carbon is only 24 g / mol, that is 52%.

Further information on soot can be found on the detailed "Soot" page of the Energy Lexicon.

coke is a porous fuel with a large surface area. It is produced from coal by heating it in the absence of oxygen [4]. This process is known as coking.

For more information on coke, please refer to the Wikipedia article "Coke".

Charcoal is even more porous than coke. It arises when burning dry wood, also in the absence of air. The wood must be heated to approx. 275 ºC. Then the wood burns, an exothermic process that increases the temperature to 350 to 400 ºC [5].

Artificial forms of graphite

An important form of graphite - also for school lessons - that does not occur in nature (in contrast to soot, coke and charcoal, which can arise in natural combustion processes, which often lead to a lack of oxygen) is this Activated carbon.

Activated carbon is a very fine crystalline and loose form of graphite, which is characterized by a very, very large surface. One gram of activated carbon has an internal surface area of ​​no less than 1000 m2 [3]. Activated charcoal is obtained by ore from wood, animal waste or cane sugar. In order to obtain such a large surface, however, foreign materials are added to the activated carbon, for example zinc chloride. These materials prevent the carbon skeleton from collapsing when heated, and so the large internal surface area is retained.

Swell:

  1. Römpp Chemie-Lexikon, 9th edition 1992
  2. Wikipedia article "Graphite", accessed May 17, 2020
  3. Riedel, Jannik, Inorganic Chemistry, Berlin 2007, pp. 515ff.
  4. Wikipedia, article "Coke", accessed May 17, 2020
  5. Wikipedia article "Charcoal", accessed May 17, 2020