Homework Assignment 18

2SDC #1-6 p. 204

1. An allotrope is two or more forms of an element in the same state that have distinctly different physical and/or chemical properties.

2. Two elements other than carbon that form allotropes are oxygen and silicon.

3. 

• a. Their properties are different. A diamond is an extremely hard substance, not electrically conductive, and is expensive. Coal is combustible and cheap. Graphite (pencil lead) is electrically conductive, common, and cheap.
• b. Their properties are different because they are allotropes of carbon and have different atomic arrangements.
• c. The differences in the costs of these substances is the hardness and rareness of diamonds versus the softness and commonness of coal and graphite.

4. Natural materials are uncontrolled and untouched, whereas engineered materials are developed by scientists to enhance natural materials through manufacturing methods.

5. Two advantages of using engineered ceramics in high-temperature applications are they are durable and have high melting points. Two disadvantages of using engineered ceramics in high-temperature applications are they are brittle and when quickly exposed to extreme temperatures, they crack.

6. Plastics can be both soft and hard. They can be squishy (ex: water bottle), or made to be extremely hard (ex: glass). They can also be converted into optical fibers, replacing copper wires and supplying incredible communication.