Final answer:
The full electron configuration for sulfur is 1s² 2s² 2p⁶ 3s² 3p⁴. When forming a monatomic ion in binary ionic compounds, sulfur becomes S²⁻ with the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶.
Step-by-step explanation:
The full electron configuration for the element sulfur (S) is 1s² 2s² 2p⁶ 3s² 3p⁴. Sulfur has six valence electrons in its outermost shell (3s and 3p orbitals), which is reflected in its electron configuration. When sulfur forms a monatomic ion, such as in binary ionic compounds, it generally gains two electrons to achieve a full outer shell, similar to the noble gas argon. This results in the formation of a sulfide ion (S²⁻) with the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶.
In binary ionic compounds that include sulfur, the most common ion is the sulfide ion S²⁻, and it is this ion with the electron configuration resembling that of argon, which stabilizes it energetically.