1. Allotropes are different forms of an element that each have distinctly different physical or chemical properties, but whose forms are in the same state.
2. Oxygen and boron form allotropes.
3.
a. A diamond is the hardest substance known, not electrically conductive, has an extremely high melting point, and is expensive. Coal is combustible and cheap. Pencil lead is a useful lubricant, a conductor of electricity, extremely soft, common, cheap, and made out of graphite.
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.While the makeup of natural materials is uncontrolled and untouched, engineered materials are developed to enhance natural materials through manufacturing methods that carefully control the microstructure of the materials.
5. The advantages of ceramics are that they are durable. have high melting points, and strength and high temperatures. The disadvantages of ceramics are that they are brittle and when rapidly exposed to high or low temperatures, the will crack.
6. 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 fantastic and noise free communication systems with high capacities.
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