KALLISTA IMAGES / CUSTOM MEDICAL STOCK PHOTO / SCIENCE PHOTO LIBRARY KALLISTA IMAGES / CUSTOM MEDICAL STOCK PHOTO / SCIENCE PHOTO LIBRARY
Graphite, molecular model. Graphite is used in pencil leads and as a lubricant. It is composed of parallel layers of hexagonally arranged carbon atoms (blue spheres). This model shows one layer. Within each layer the carbon atoms are linked by strong covalent bonds, while the parallel layers are linked together by weak Van der Waals' forces. This Van der Waals' bonding is strong enough to hold the layers together, yet weak enough to let them slide over each other. This confers graphite's softness and its ability to act as a lubricant.
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