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.

   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
2. 2.

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

   • Al₂O₃, because two Al³⁺ (+6) cancel three O²⁻ (−6)
   • Al₃O₂, because the subscripts swap places
   • AlO, because one aluminum atom pairs with one oxygen atom
3. 3.

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

   • Mg₃N₂, because three Mg²⁺ (+6) cancel two N³⁻ (−6)
   • Mg₂N₃, because the subscripts swap places
   • MgN, because one magnesium atom pairs with one nitrogen atom
4. 4.

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

   • Sr₂O, because the subscripts swap places
   • SrO, because one Sr²⁺ already cancels one O²⁻
   • SrO₂, because oxygen usually comes in pairs in a formula
5. 5.

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

   • 2 Al + O₂ → 2 AlO, with one Al for each O
   • 4 Al + 3 O₂ → 2 Al₂O₃, using Al³⁺ and O²⁻
   • 2 Al + 3 O₂ → 2 AlO₃, with 3 oxygen in each product
6. 6.

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

   • 3 Mg + N₂ → Mg₃N₂, using Mg²⁺ and N³⁻
   • Mg + N₂ → MgN₂, with N₂ moved into the product
   • 2 Mg + N₂ → 2 MgN, with one Mg for each N
7. 7.

   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

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 falls down the group, because bigger atoms hold their outer electron more tightly
   • Reactivity stays the same down the group, since each metal has one outer electron
   • 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?

    • Chlorine with sodium bromide: chlorine pulls electrons harder (3.16 to 2.96)
    • Both react, since the halogens each gain one electron
    • Iodine with sodium bromide: iodine is larger, so it takes electrons more easily
12. 10.

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

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