18-21 p. 182, 1-6 p.204

18. The difference between reusing and recycling is that recycling is converting waste into usable material, and reusing is to use more than once.

19. a. renewable resources: solar energy, wind power, tides, hydroelectricity
      b. nonrenewable resources: petroleum, coal, natural gas, nuclear energy


20. a. reusing
      b. recycling
      c. reusing

21. They are both made, packed, shipped, used, disposed, and hopefully recycled.

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

allotropes of carbon

2. oxygen:O₂ oxygen gas  O₃ ozone

   sulfur

allotropes of sulfur

3. a. How their properties are different is because they all contain carbon just in different forms of the element,

    b. Why their properties are different because they have distinctly different atomic arrangements.

    c. What accounts for the differences in the cost of these items are the reactivity, abundance, and need for the item.

4. Engineered materials are more likely to be more stable and sturdier than natural materials because of the other material that they put in it.

5. Two advantages: low chemical reactivity and resistance to wear.

    Two disadvantages; brittleness and they can fracture if exposed to rapid temperatures.

ceramics at a high temperature

6 Two properties that can be modified in plastics to make them useful for new applications are making them safe to be exposed to sunlight and to resist wear and tear.