Try this:. Rotate the Graphite molecule. Hold the left mouse button down over the image and move the mouse to rotate the graphite molecule. Notice that graphite is layered. While there are strong covalent bonds between carbon atoms in each layer, there are only weak forces between layers.
This allows layers of carbon to slide over each other in graphite. On the other hand, in diamond each carbon atom is the same distance to each of its neighboring carbon atoms. In this rigid network atoms cannot move. This explains why diamonds are so hard and have such a high melting point. Try this!! Rotate the structure of diamond Notice that each diamond atom is the same distance to each of its neighboring carbon atoms.
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.
Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. 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.
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