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.

   Aluminum (group 13) combines with oxygen (group 16). Which formula is predicted, Jun?

   • Al₃O₂, because the subscripts swap places
   • Al₂O₃, because two Al³⁺ (+6) cancel three O²⁻ (−6)
   • AlO, because one aluminum atom pairs with one oxygen atom
5. 5.

   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
6. 6.

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

   • SrO₂, because oxygen usually comes in pairs in a formula
   • SrO, because one Sr²⁺ already cancels one O²⁻
   • Sr₂O, because the subscripts swap places
7. 7.

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

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

8. Read this first

   Group 1 metals (real data, rounded)

   element	metallic radius (pm)	first ionization energy (kJ/mol)
   lithium	152	520
   sodium	186	496
   potassium	227	419
   rubidium	248	403

9. 8.

   Ren reads the table. Which statement about the group 1 metals is best supported?

   • Reactivity stays the same down the group, since each metal has one outer electron
   • Reactivity falls down the group, because bigger atoms hold their outer electron more tightly
   • Down the group the outer electron is lost more easily, so reactivity should rise

10. Halogens (real data, rounded)

    halogen	electronegativity
    fluorine	3.98
    chlorine	3.16
    bromine	2.96
    iodine	2.66

11. 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)
12. 10.

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

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