Ions and Formula Units

Ions and Formula Units

Read each question carefully and answer to the best of your ability. For multiple choice questions, circle the correct option.

What are Ions?

An atom is made of protons, neutrons, and electrons. Protons have a positive (+) charge, electrons have a negative (-) charge, and neutrons have no charge. Normally, an atom has an equal number of protons and electrons, making it electrically neutral. However, sometimes atoms can gain or lose electrons. When an atom gains or loses electrons, it becomes an ion, which has an overall electric charge.

If an atom loses electrons, it becomes a positive ion (cation). If an atom gains electrons, it becomes a negative ion (anion).

1. What particle in an atom has a negative charge?

2. An atom that loses electrons becomes a   ion.

3. An atom is electrically neutral because it has an equal number of protons and  .

4. When an atom gains electrons, it forms a   ion.

5. Ions are atoms that have an overall electric  .

6. Explain the difference between a cation and an anion.

7. Neutrons have a positive charge.

8. An ion is an atom that has gained or lost electrons.

Formula Units

When positive and negative ions come together, they form an ionic compound. The smallest whole-number ratio of ions that creates a neutral compound is called a formula unit. For example, sodium (Na+) and chlorine (Cl-) combine to form sodium chloride (NaCl). The formula unit is NaCl because one Na+ ion balances one Cl- ion.

9. If a magnesium ion has a +2 charge (Mg²⁺) and an oxygen ion has a -2 charge (O²⁻), what would be the formula unit for magnesium oxide?

10. If a calcium ion has a +2 charge (Ca²⁺) and a chloride ion has a -1 charge (Cl⁻), what would be the formula unit for calcium chloride?