4. If yellow spheres represent sulfur atoms and red spheres represent oxygen atoms, which of the following drawings shows a collection of sulfur dioxide molecules? Which drawing represents a mixture?
2.25

5. Assume that the mixture of substances in drawing (a) undergoes a reaction. Which of the drawings (b)–(d) represents a product mixture consistent with the law of mass conservation?
2.26

6. If red and blue spheres represent atoms of different elements, which two of the following drawings illustrate the law of multiple proportions?
2.27

7. Give molecular formulas corresponding to each of the following ball-and-stick molecular representations (red = O, gray = C, blue = N, ivory = H). In writing the formula, list the atoms in alphabetical order.
2.28

8. Which of the following drawings represents an Na atom. A Ca2+ ion
Which of the following drawings represents an Na atom? A Ca2+ ion? An F ion?
2.29

9. Indicate where in the periodic table the following elements are found:
(a) Elements that commonly form anions
(b) Elements that commonly form cations
(c) Elements that commonly form covalent bonds
2.30

10. In the following drawings, red spheres represent cations and blue spheres represent anions. Match each of the drawings (a)–(d) with the following ionic compounds:
(a) Ca3(PO4)2 (b) LiCO3
(c) FeCl2 (d) MgSO4
2.31