Question

why is the calcium ion (ca²⁺) more stable than the calcium atom (ca)?
a) the noble gas configuration is more stable.
b) eighteen electrons are less stable than twenty electrons.
c) the two electrons more than the noble gas configuration is more stable.
d) twenty electrons are more stable than eighteen electrons.

Explanation:

Calcium atom (Ca) has 20 electrons with an electron configuration of \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}\). When it loses 2 electrons to form \(Ca^{2 +}\), it has 18 electrons and attains the electron configuration of the noble gas argon (\(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}\)). Noble gas configurations (with full - filled valence shells) are more stable due to the lower energy state associated with having complete octets (or duplets for the first shell). Option B is incorrect because 18 (noble gas configuration) is more stable than 20 (for Ca atom). Option C is wrong as having two more electrons than noble gas configuration (like in Ca atom) is less stable. Option D is incorrect as 18 (in \(Ca^{2+}\)) is more stable than 20 (in Ca atom).

Answer:

A. The noble gas configuration is more stable.