Question

why is the calcium ion (ca²⁺) more stable than the calcium atom (ca)?

a) twenty electrons are more stable than eighteen electrons.

b) eighteen electrons are less stable than twenty electrons.

c) the noble gas configuration is more stable.

d) the two electrons more than the noble gas configuration is more stable.

Explanation:

To determine why \( \text{Ca}^{2+} \) is more stable than \( \text{Ca} \), we analyze the electron configurations:

• A calcium atom (\( \text{Ca} \)) has 20 electrons, with the configuration \( 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 \).
• A calcium ion (\( \text{Ca}^{2+} \)) loses 2 electrons from the \( 4s \) orbital, resulting in 18 electrons and the configuration \( 1s^2 2s^2 2p^6 3s^2 3p^6 \), which matches the noble gas argon (\( \text{Ar} \)).

Noble gas configurations (filled valence shells) are highly stable because they have no unpaired electrons and minimal electron-electron repulsion.

• Option A: 20 electrons (Ca atom) are not more stable than 18 (Ca²⁺); noble gas configs (18 e⁻ here) are stable. Eliminate A.
• Option B: 18 electrons (noble gas config) are more stable than 20, so this is incorrect. Eliminate B.
• Option C: \( \text{Ca}^{2+} \) has a noble gas configuration (matches Ar), which is more stable. This is correct.
• Option D: \( \text{Ca}^{2+} \) has the noble gas config (not two electrons more), so this is false. Eliminate D.

Answer:

C. The noble gas configuration is more stable.