Which equation correctly represents the first ionization of calcium?

• A. Ca(s) → Ca^+(aq) + e^-
• B. Ca(g) → Ca^+(g) + e^-
• C. Ca^+(g) → Ca^{2+}(g) + e^-
• D. Ca(g) + e^- → Ca^-(g)

Answer: (B)

Verified step by step guidance

1. Understand that the first ionization energy refers to the process of removing one electron from a neutral atom in the gas phase to form a singly charged positive ion.
2. Recognize that ionization involves gaseous atoms, not solid or aqueous species, because ionization energies are defined for isolated atoms in the gas phase.
3. Write the general form of the first ionization process as: \(\mathrm{Ca}(g) \rightarrow \mathrm{Ca}^+(g) + e^-\), where a neutral calcium atom loses one electron to form a calcium ion with a +1 charge.
4. Note that the equation \(\mathrm{Ca}(s) \rightarrow \mathrm{Ca}^+(aq) + e^-\) is incorrect because it involves a solid and aqueous species, which is not the standard state for ionization energy measurements.
5. Confirm that the other options either represent further ionization steps (like \(\mathrm{Ca}^+(g) \rightarrow \mathrm{Ca}^{2+}(g) + e^-\)) or electron gain (like \(\mathrm{Ca}(g) + e^- \rightarrow \mathrm{Ca}^-(g)\)), which are not first ionization processes.