Pure Substances and Elements.

1. What defines pure substances?

2. How many known elements are there?

3. Who devised the periodic table of elements?

4. What is the only letter that does not appear in the periodic table of elements? 

5. How was the discovery of Helium first made?

6. What is the chemical symbol for Mercury, and what does it mean?

7. What are the characteristics of metals, nonmetals, and metalloids?

8. How are compounds defined?

9. What information does the chemical formula of a compound provide?

10.What does the subscript in a chemical formula indicate?