1) What is an allotrope?
An allotrope is a different form of an element that has distinctly different physical or chemical properties.
2) Name two elements other than carbon that form allotropes.
Oxygen, silicon, and phosphorus form allotropes as well.
3) A diamond, a chunk of coal, and your pencil lead contain the same substance:
a. How are their properties different?
b. Why are their properties different?
c. What accounts for the differences in the cost of these items?
a. A diamond is the hardest substance known, not electrically conductive, has an extremely high melting point, and is rare; therefore, 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) How do engineered materials differ from natural materials?
Engineered materials are materials developed by scientists and engineers to enhance natural materials through manufacturing methods that carefully control the microstructure of the materials; the makeup of natural materials, however, is uncontrolled and untouched.
5) List two advantages and two disadvantages of using engineered ceramics in high-temperature applications.
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.
6) Describe two examples of properties that can be modified in plastics to make them useful for new applications.
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 fantastic and noise free communication systems with high capacities.
Is a brown colored coal that is a soft fuel with characteristics that put it somewhere between coal and peat. This coal has a carbon content of around 25-35%. The carbon content is an indicator or its purity for fuel. Having a high moisture content of brown coal, carbon dioxide emissions from brown coal fired plants are generally much higher than for comparable black coal plants. This is clearly not a home heating type of coal.
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