Predict a simple reaction from the outer electrons

Answer Key - Grade 10 Science Worksheet - Challenge Me

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

1. 1.

   Ari reacts 8 aluminum atoms (group 13) with oxygen gas (group 16). Electrons lost must equal electrons gained. How many O₂ molecules are used?

   6 molecules
2. 2.

   Bo reacts 12 magnesium atoms (group 2) with nitrogen gas (group 15). Electrons lost must equal electrons gained. How many N₂ molecules are used?

   4 molecules
3. 3.

   Esme reacts 12 lithium atoms (group 1) with oxygen gas (group 16). Electrons lost must equal electrons gained. How many O₂ molecules are used?

   3 molecules
4. 4.

   X is a main-group metal that forms X₂O₃ with oxygen. Which group is X in, Jun?

   • Group 13, since each X atom loses 3 electrons
   • Group 2, since each X atom loses 2 electrons
   • Group 15, since each X atom gains 3 electrons
5. 5.

   A compound has the formula M₃X₂. Which pair of ion charges fits, Kira?

   • M³⁺ and X²⁻, since the subscripts swap places
   • M²⁺ and X³⁻, since 3 × (+2) cancels 2 × (−3)
   • M²⁺ and X²⁻, since both ions carry the same size of charge

6. Read this first

   Magnesium reacting with nitrogen (example data)

   measurement	value
   magnesium used (g)	1.215
   product formed (g)	1.683
   magnesium molar mass (g/mol)	24.3
   nitrogen molar mass (g/mol)	14.0

7. 6.

   Using the table, which formula does the product have, Luz?

   • Mg₃N₂: 0.0500 mol of Mg to 0.0334 mol of N is 3 to 2
   • Mg₂N₃: the mole ratio of Mg to N is 2 to 3
   • MgN: one magnesium atom pairs with one nitrogen atom

8. Group 2 metals (real data, rounded)

   element	first ionization energy (kJ/mol)
   magnesium	738
   calcium	590
   strontium	550

9. 7.

   A student says magnesium and calcium are both group 2, so they react at the same speed. Which reply is best supported, Noah?

   • Supported: both lose 2 electrons, so they should react at the same speed with water or acid
   • Supported: group 2 metals are the same in each property, since they share one group
   • Weak: same outer electrons give the same formula, but calcium gives them up more easily (590 vs 738)

10. Element A ionization energies (real data, rounded)

    step	energy (kJ/mol)
    first	496
    second	4,562
    third	6,910

11. 8.

    Using the table, how many outer electrons does element A have, Ren?

    • 3: three energies are listed, so three electrons can be removed
    • 1: the energy jumps from 496 to 4,562 after the first electron
    • 2: the energy rises by about 4,000, which counts two electrons

12. Element B ionization energies (real data, rounded)

    step	energy (kJ/mol)
    first	738
    second	1,451
    third	7,733

13. 9.

    Element B is a metal. Using the table, which formula does it form with chlorine, Tala?

    • BCl₃, since three energies are listed
    • BCl, since the first electron comes off most easily
    • BCl₂, since the big jump comes after the second electron

14. Elements B and D ionization energies (real data, rounded)

    step	element B (kJ/mol)	element D (kJ/mol)
    first	738	578
    second	1,451	1,817
    third	7,733	2,745
    fourth	not listed	11,577

15. 10.

    Which element, B or D, is more likely to form a 3+ ion, Zee?

    • D: energies rise gently through the third electron, then jump at the fourth
    • B: its third energy, 7,733, is the largest in the table and so the most telling
    • Both: each table lists a third energy, so each can lose three electrons