Question

part 2: classify the following substances as elements (e) or compounds (c).
______7. mercury
______8. water
______9. carbon dioxide
______10. iron
______11. aluminum
______12. oxygen (o₂)

Explanation:

To solve this, we recall: An element (E) is a pure substance made of only one type of atom. A compound (C) is a pure substance made of two or more different elements chemically combined.

7. Mercury

Mercury (Hg) is a single type of atom (atomic number 80). So it is an element.

Answer:

E

8. Water

Water has the formula $\ce{H_2O}$, made of hydrogen and oxygen atoms. It is a compound.