Homework due on July 18

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 with a high melting point, it is not electrically conductive, and it is costly because it is hard to find. Coal is combustible, easy to obtain, and is fairly cheap. Pencil lead is electrically conductive and easy to find, also making it cheap.
    b. There properties are different because of the organization of atoms within each element.
    c. The difference in the cost of these items all depends on what is easiest to find and manufacture. Diamonds are hard to manufacture because they are expensive, rare, and very hard. Coal, on the other hand, is cheap and easy to find. 

4. Engineered materials are materials made by scientists and engineers to enhance natural materials through manufacturing methods.


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.