This page relates the structures of covalent network solids to the physical properties of the substances. Carbon has an electronic arrangement of 2,4.
In diamond, each carbon shares electrons with four other carbon atoms - forming four single bonds. In the diagram some carbon atoms only seem to be forming two bonds or even one bond , but that's not really the case. We are only showing a small bit of the whole structure. This is a giant covalent structure - it continues on and on in three dimensions. It is not a molecule, because the number of atoms joined up in a real diamond is completely variable - depending on the size of the crystal.
Don't try to be too clever by trying to draw too much of the structure! Learn to draw the diagram given above. Do it in the following stages:. Practice until you can do a reasonable free-hand sketch in about 30 seconds. Graphite has a layer structure which is quite difficult to draw convincingly in three dimensions. The diagram below shows the arrangement of the atoms in each layer, and the way the layers are spaced. Notice that you cannot really draw the side view of the layers to the same scale as the atoms in the layer without one or other part of the diagram being either very spread out or very squashed.
In that case, it is important to give some idea of the distances involved. The distance between the layers is about 2. The layers, of course, extend over huge numbers of atoms - not just the few shown above. You might argue that carbon has to form 4 bonds because of its 4 unpaired electrons, whereas in this diagram it only seems to be forming 3 bonds to the neighboring carbons.
This diagram is something of a simplification, and shows the arrangement of atoms rather than the bonding. Each carbon atom uses three of its electrons to form simple bonds to its three close neighbors. That leaves a fourth electron in the bonding level. These "spare" electrons in each carbon atom become delocalized over the whole of the sheet of atoms in one layer.
They are no longer associated directly with any particular atom or pair of atoms, but are free to wander throughout the whole sheet. The important thing is that the delocalized electrons are free to move anywhere within the sheet - each electron is no longer fixed to a particular carbon atom. There is, however, no direct contact between the delocalized electrons in one sheet and those in the neighboring sheets. Fullerenes also called buckyballs are molecules of varying sizes composed entirely of carbon that take on the form of hollow spheres, ellipsoids, or tubes.
Buckyballs and buckytubes have been the subject of intense research, both because of their unique chemistry and for their technological applications, especially in materials science, electronics, and nanotechnology.
Carbon nanotubes are cylindrical carbon molecules that exhibit extraordinary strength and unique electrical properties and are efficient conductors of heat. Nanobuds therefore exhibit properties of both nanotubes and fullerenes. Glassy or vitreous carbon is a class of carbon widely used as an electrode material in electrochemistry as well as in prosthetic devices and high-temperature crucibles. Its most important properties are high temperature resistance, hardness, low density, low electrical resistance, low friction, low thermal resistance, extreme resistance to chemical attack, and impermeability to gases and liquids.
Other allotropes of carbon include carbon nanofoam, which is a low-density cluster assembly of carbon atoms strung together in a loose three-dimensional web; pure atomic and diatomic carbon; and linear acetylenic carbon, which is a one-dimensional carbon polymer with the structure - CC n -.
Boundless vets and curates high-quality, openly licensed content from around the Internet. This particular resource used the following sources:. Skip to main content. Nonmetallic Elements. Search for:. Allotropes of Carbon. Learning Objective Describe the properties of the allotropes of carbon. Key Points Diamond is a well-known allotrope of carbon that exhibits hardness and high dispersion of light.
It is the hardest known natural mineral and finds applications in cutting, drilling, and jewelry, and as a potential semiconductor material. Graphene is a single layer of carbon atoms arranged in one plane; layers of graphene make up graphite. Graphene is a material of interest due to its high electron mobility and its possible applications in electronics.
Fullerenes are a class of carbon allotropes in which carbon takes the form of a hollow sphere, ellipsoid, or tube. These atoms have two types of interactions with one another. In the first, each carbon atom is bonded to three other carbon atoms and arranged at the corners of a network of regular hexagons with a degree C-C-C bond angle.
These planar arrangements extend in two dimensions to form a horizontal, hexagonal "chicken-wire" array.
In addition, these planar arrays are held together by weaker forces known as stacking interactions. The distance between two layers is longer 3. This three-dimensional structure accounts for the physical properties of graphite.
Unlike diamond, graphite can be used as a lubricant or in pencils because the layers cleave readily. It is soft and slippery, and its hardness is less than one on the Mohs scale. Graphite also has a lower density 2. The planar structure of graphite allows electrons to move easily within the planes. This permits graphite to conduct electricity and heat as well as absorb light and, unlike diamond, appear black in color.
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