2SDS (p.204) #1-6

7/17/13

1. Allotropes are different forms of the same element that each have distinctly different physical or chemical properties.

2. Oxygen and silicon are two other elements other than carbon that form allotropes.

3. a. A diamond is an extremely hard substance, has a high melting point, not electrically conductive, and is expensive because it is rare. Coal is combustible (burn) and cheap. Pencil lead (graphite) is electrically conductive and common; therefore, cheap.
    b. There properties are different because of the way the atoms of elements are linked together and organized.
    c. The difference in the cost of these items is due to the high melting point, hardness, and rarity of the diamond, which causes the diamond to be more expensive. Where as in graphite and coal they are more reactive and common, which makes them cheaper.

4. Engineered materials are materials made by scientists and engineers to enhance the natural materials through manufacturing methods. However, natural materials can't be controlled, so you basically get what is there.

5. Two advantages of using high ceramics in high- temperature applications are they can operate at higher temperatures and still keep their strength. They are also durable, meaning they can withstand pressure. Two disadvantages of using ceramics is that they are brittle and can break easily if exposed to rapid temperature change, like hot to cold in engines.

6. Two examples of properties that can be modified in plastics to make them useful for new applications are one plastic can be both hard and soft. Like polyethylene, which can be made to display either soft and pliable properties (squeezing a bottle for water) or crafted to be hard and brittle (glasslike). Plastic can also be made into optical fibers, which will replace copper wires in phones and data transmission lines for communication.