1. Allotropes are forms of an element in the same state.
2. Oxygen and silicon also form allotropes.
3. a. A diamond is the hardest substance known, is is not electrically conductive, and it has an extremely high melting point. It is also rare, making it is very expensive. Coal is very combustible and cheap. Pencil lead, made of graphite, is a useful lubricant, a conductor of electricity, extremely soft, and very common and cheap.
b. Their properties are different because although they are made of the same element, they are allotropes of carbon, and therefore, have very different atomic arrangements. c. The rigid, three dimensional structure of carbon atoms in diamonds indicates its high melting point, hardness, and rareness that accounts for its high cost. The atomic makeup of graphite and coal indicate their much more common, more reactive, and softer properties, and therefore, their cheaper prices.
4. Engineered materials are materials developed by scientists and engineers to enhance natural materials through manufacturing methods that carefully control the microstructure of the materials. On the other hand, the makeup of natural materials, however, is uncontrolled and untouched.
5. Ceramics are durable and have high melting points and strength at high temperatures. However, ceramics are also brittle and when rapidly exposed to high and low temperatures, will crack or break.
6. Plastics can be customized to be either soft or hard. For example, polyethylene can be tailored to display soft properties, such as a squeeze bottle for water, or tailored to be hard and brittle, like glass. Plastic can also be made into optical fibers, which replace copper wires and provide noise free communication systems with high capacities.
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