1. An allotrope is a different form of an element that has distinctly different physical properties, but has to be in the same state as the original element (for example solid iron and molten iron have different properties but are not allotropes since one is a liquid).
2. Oxygen and aluminum both form allotropes.
3. Diamond, coal, and pencil lead:
a. Diamond is a hard substance, does not conduct electricity, and is colorless. Coal is powdery and used for fuel. Graphite is black, slippery, electrically conductive, and soft.
b. Their properties vary because of their structures. Diamond has tightly knit bonds, while graphite’s bonds are looser, making it an ideal lubricant.
c. The appearance, quality, usefulness, and quantity account for their costs.
4. Engineered materials sometimes have different properties than their original substances to make them more durable and useful for a job.
5. Ceramics can operate at high temperatures, rather than metals, and have very high melting points. However, ceramics are very brittle and can crack during rapid changes in temperature. For example, when an engine starts cooling down the ceramic will crack and could lead to engine failures.
6. To make plastics more useful, increasing their resistance to heat would be useful. For example, accidentally placing a plastic plate on a hot surface will cause it to melt resulting in a sticky mess. Increasing their melting points would help avoid these inconveniences. Also, finding a new way to make plastics would decrease pollution and waste caused by plastic materials. Inventing a decomposable substance that is renewable would greatly please the public.
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