Predict a simple reaction from the outer electrons

Answer Key - Grade 10 Science Worksheet

Circle the best answer, or write your answer on the line.

1. 1.

   Aluminum (group 13) reacts with oxygen (group 16) to form Al₂O₃. How many electrons move in all to make one Al₂O₃ unit, Ari?

   6 electrons
2. 2.

   Magnesium (group 2) reacts with nitrogen (group 15) to form Mg₃N₂. How many electrons move in all to make one Mg₃N₂ unit, Bo?

   6 electrons
3. 3.

   Sodium (group 1) reacts with sulfur (group 16) to form Na₂S. How many electrons move in all to make one Na₂S unit, Esme?

   2 electrons
4. 4.

   Magnesium (group 2) combines with nitrogen (group 15). Which formula is predicted, Kira?

   • MgN, because one magnesium atom pairs with one nitrogen atom
   • Mg₃N₂, because three Mg²⁺ (+6) cancel two N³⁻ (−6)
   • Mg₂N₃, because the subscripts swap places
5. 5.

   Strontium (group 2) combines with oxygen (group 16). Which formula is predicted, Luz?

   • SrO₂, because oxygen usually comes in pairs in a formula
   • Sr₂O, because the subscripts swap places
   • SrO, because one Sr²⁺ already cancels one O²⁻
6. 6.

   Which balanced equation shows aluminum burning in oxygen gas, Milo?

   • 4 Al + 3 O₂ → 2 Al₂O₃, using Al³⁺ and O²⁻
   • 2 Al + 3 O₂ → 2 AlO₃, with 3 oxygen in each product
   • 2 Al + O₂ → 2 AlO, with one Al for each O
7. 7.

   Which balanced equation shows magnesium reacting with nitrogen gas, Noah?

   • 2 Mg + N₂ → 2 MgN, with one Mg for each N
   • 3 Mg + N₂ → Mg₃N₂, using Mg²⁺ and N³⁻
   • Mg + N₂ → MgN₂, with N₂ moved into the product
8. 8.

   Which balanced equation shows aluminum reacting with chlorine gas, Pia?

   • 2 Al + 3 Cl₂ → 2 AlCl₃, using Al³⁺ and Cl⁻
   • Al + Cl₂ → AlCl₂, with Cl₂ moved into the product
   • Al + 3 Cl₂ → AlCl₃, with three Cl₂ for one Al

9. Read this first

   Halogens (real data, rounded)

   halogen	electronegativity
   fluorine	3.98
   chlorine	3.16
   bromine	2.96
   iodine	2.66

10. 9.

    Using the table, which pair reacts: chlorine gas with sodium bromide solution, or iodine with sodium bromide solution, Tala?

    • Iodine with sodium bromide: iodine is larger, so it takes electrons more easily
    • Both react, since the halogens each gain one electron
    • Chlorine with sodium bromide: chlorine pulls electrons harder (3.16 to 2.96)
11. 10.

    Strontium is in group 2, below calcium. Which equation predicts its reaction with oxygen gas, Zee?

    • Sr + O₂ → SrO₂
    • 2 Sr + O₂ → 2 SrO
    • 4 Sr + O₂ → 2 Sr₂O