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?

   • Mg₂N₃, because the subscripts swap places
   • Mg₃N₂, because three Mg²⁺ (+6) cancel two N³⁻ (−6)
   • MgN, because one magnesium atom pairs with one nitrogen atom
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
   • SrO, because one Sr²⁺ already cancels one O²⁻
   • Sr₂O, because the subscripts swap places
6. 6.

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

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

   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
8. 8.

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

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

9. 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

10. 9.

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

    • Down the group the outer electron is lost more easily, so reactivity should rise
    • 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

11. Halogens (real data, rounded)

    halogen	electronegativity
    fluorine	3.98
    chlorine	3.16
    bromine	2.96
    iodine	2.66

12. 10.

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

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