Read a chemical formula and its ball-and-stick model

Grade 8 Science Worksheet - Challenge Me

Circle the best answer.

1. 1.

   Ari draws 3 CO₂ for three carbon dioxide molecules from a big sigh. How many oxygen atoms do 3 CO₂ hold in all?

   • 2 oxygen atoms
   • 5 oxygen atoms
   • 6 oxygen atoms
   • 9 oxygen atoms
2. 2.

   On the board, Bo sees 2 NH₃, which means two ammonia molecules. How many hydrogen atoms do 2 NH₃ hold in all?

   • 8 hydrogen atoms
   • 5 hydrogen atoms
   • 6 hydrogen atoms
   • 3 hydrogen atoms
3. 3.

   Esme writes 4 H₂O for four water molecules in a very small puddle. How many oxygen atoms do 4 H₂O hold in all?

   • 5 oxygen atoms
   • 4 oxygen atoms
   • 8 oxygen atoms
   • 1 oxygen atom
4. 4.

   Jun's ethane model has 2 C balls in a row. Each C has 3 H balls on it. Sticks join every pair. Which formula matches?

   • C₂H₇
   • C₂H₃
   • C₂H₆
   • C₆H₂
5. 5.

   At camp, Kira's little stove runs on propane. The model has 3 C balls in a row; each end C has 3 H balls, the middle one 2. Which formula matches?

   • C₈H₃
   • C₃H₈
   • C₃H₁₀
   • C₃H₆
6. 6.

   Luz's butane model has 4 C balls in a row. Each end C has 3 H balls; each middle C has 2. Which formula matches the model?

   • C₄H₈
   • C₄H₁₃
   • C₁₀H₄
   • C₄H₁₀
7. 7.

   Milo says a CO₂ molecule has two carbon atoms, because of the 2 in the formula. Agree or disagree?

   • Disagree: the 2 counts the oxygen atoms
   • Disagree: it has 3 carbon atoms
   • Disagree: it has no carbon, as C has no number
   • Agree: the 2 counts the carbon atoms
8. 8.

   Pia reads 2 O₂ in a book and says it means 2 oxygen atoms in all. Agree or disagree?

   • Disagree: it means 3 oxygen atoms
   • Agree: one O₂ has 2 atoms
   • Disagree: it means 4 oxygen atoms
   • Agree: the big 2 just repeats the small 2
9. 9.

   Ren checks classmates' models of hydrogen peroxide, H₂O₂. Which model has the right balls?

   • 3 balls: 2 lettered H and 1 lettered O
   • 4 balls: 1 lettered H and 3 lettered O
   • 4 balls: 2 lettered H and 2 lettered O
   • 2 balls: 1 lettered H and 1 lettered O
10. 10.

    Tala is building ethylene, C₂H₄, to show the class. Which set of balls is right?

    • 2 balls: 1 lettered C and 1 lettered H
    • 8 balls: 2 lettered C and 6 lettered H
    • 6 balls: 2 lettered C and 4 lettered H
    • 6 balls: 4 lettered C and 2 lettered H