Write formulas for ionic compounds

Answer Key - Grade 10 Science Worksheet

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

1. 1.

   A student writes a formula with 3 aluminum ions (+3 each) and 2 oxide ions (−2 each). What is its net charge, Ari?

   5
2. 2.

   A student writes a formula with 3 calcium ions (+2 each) and 2 chloride ions (−1 each). What is its net charge, Esme?

   4

3. Read this first

   Use this

   Balancing charges with the least common multiple (worked examples). Columns: compound, cation charge, anion charge, LCM, ions in the formula. MgO, +2, −2, 2, 1 Mg²⁺, 1 O²⁻; CaCl₂, +2, −1, 2, 1 Ca²⁺, 2 Cl⁻; Al₂O₃, +3, −2, 6, 2 Al³⁺, 3 O²⁻.

4. 3.

   Using the table, why does Al₂O₃ have 2 aluminum ions, Jun?

   • 3 ÷ 2 = 2
   • 6 ÷ 2 = 2
   • 6 ÷ 3 = 2
5. 4.

   Using the table, why is MgO written with one of each ion, Kira?

   • +2 and −2 already balance
   • Magnesium has just one shell left
   • Oxygen is lighter
6. 5.

   Using the table, what is the total positive charge in one Al₂O₃ unit, Luz?

   • +3
   • +6
   • +5
7. 6.

   What is the formula for aluminum oxide, Noah?

   • Al₂O₃
   • Al₃O₂
   • AlO
8. 7.

   Which is written first in an ionic formula, Pia?

   • The lighter ion
   • The nonmetal
   • The metal
9. 8.

   What does the formula NaCl tell you about table salt, Ren?

   • Na⁺ and Cl⁻ are in a 1 : 1 ratio
   • It has one single ion
   • It is a molecule of two atoms
10. 9.

    What is a formula unit, Tala?

    • The smallest ratio of ions
    • A single atom
    • One shared molecule of the salt
11. 10.

    How is CaCl₂ different from H₂O, Zee?

    • H₂O is made of separate ions
    • CaCl₂ is a lattice of ions
    • CaCl₂ is a gas