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

Grade 8 Science Worksheet

Circle the best answer.

1. 1.

   Bo's cake rises thanks to baking soda, NaHCO₃. How many atoms in all does the formula NaHCO₃ show?

   • 5 atoms
   • 4 atoms
   • 6 atoms
   • 3 atoms
2. 2.

   Esme reads a laundry box: washing soda is Na₂CO₃. How many atoms in all does the formula Na₂CO₃ show?

   • 6 atoms
   • 5 atoms
   • 3 atoms
   • 9 atoms
3. 3.

   Jun's model has one ball lettered N joined to three balls lettered H. Which formula matches the model?

   • N₃H
   • NH
   • NH₄
   • NH₃
4. 4.

   Ethylene is a plant gas that helps a banana ripen. Kira's model of it has 2 C balls and 4 H balls. Which formula matches?

   • C₄H₂
   • C₂H₂
   • CH
   • C₂H₄
5. 5.

   Luz's model shows a C ball between two O balls, all in a straight line. Which formula matches the model?

   • Co₂
   • CO₂
   • C₂O
   • CO
6. 6.

   Milo bakes cookies with table sugar, sucrose, C₁₂H₂₂O₁₁. Which describes one sucrose molecule?

   • 12 carbon, 22 hydrogen and 11 oxygen atoms
   • 3 atoms in total: carbon, hydrogen and oxygen
   • 12 carbon atoms and 33 oxygen atoms
   • 1 carbon, 12 hydrogen and 22 oxygen atoms
7. 7.

   Lemons taste sour partly because of citric acid, C₆H₈O₇. Which describes one citric acid molecule, Noah?

   • 3 atoms: carbon, hydrogen and oxygen
   • 6 carbon atoms and 15 hydrogen atoms
   • 6 carbon, 8 hydrogen and 7 oxygen atoms
   • 1 carbon, 6 hydrogen and 8 oxygen atoms
8. 8.

   Symbol and name. S sulfur; Si silicon; O oxygen. Pia finds a clear quartz pebble. Quartz is silicon dioxide, SiO₂. What does the formula SiO₂ show?

   • 2 silicon atoms for every oxygen atom
   • 1 sulfur atom for every 2 oxygen atoms
   • 1 silicon atom for every 2 oxygen atoms
   • Sulfur, iodine and oxygen atoms
9. 9.

   Tala writes ethylene, C₂H₄, and ethane, C₂H₆, side by side. Do the two formulas show the same substance?

   • No: they have different numbers of hydrogen atoms
   • Yes: both have 2 carbon atoms
   • Yes: both have carbon and hydrogen
   • No: C₂H₆ has more carbon atoms
10. 10.

    In Zee's book, oxygen gas is O₂ and ozone is O₃. Both are only oxygen. Are O₂ and O₃ the same substance?

    • Yes: one extra atom changes nothing
    • No: ozone has no oxygen in it
    • No: their molecules have different numbers of atoms
    • Yes: both are made of oxygen alone