Final answer:
A magnesium atom loses two electrons to form a magnesium cation in the balanced half-reaction Mg → Mg2+ + 2e-, which covers both mass and charge balance.
Step-by-step explanation:
Writing a Balanced Half-Reaction
The process of oxidation of solid magnesium to magnesium cations involves the magnesium atoms losing electrons to become positively charged ions. The half-reaction for this process should show the change in the oxidation state of magnesium and balance both the number of atoms and the charge. To balance this half-reaction, we start with the elemental form of magnesium and its ionized form:
Mg → Mg2+
Next, we ascertain that the magnesium atom has lost two electrons to form the Mg2+ ion. These electrons are shown as products in the half-reaction, balancing for both mass and charge:
Mg → Mg2+ + 2e-
This is the balanced half-reaction for the oxidation of magnesium, which can be further explored in electrochemistry and applied to galvanic cells. Remember, balancing half-reactions is an essential skill for writing net ionic equations and understanding electrochemical processes.