The compound Na2S is correctly named sodium sulfide. The name ‘disodium monosulfide’ is not appropriate for several reasons.
Firstly, the naming convention for ionic compounds, such as Na2S, relies on the charges of the ions involved rather than using prefixes like ‘di-‘ or ‘mono-‘. Sodium (Na) is a metal that typically forms a +1 charge, while sulfide (S) is a non-metal that forms a -2 charge. In Na2S, two sodium ions balance one sulfide ion to create a neutral compound.
Using prefixes is more common in covalent compounds where the number of atoms is significant in defining the compound. In ionic compounds, the focus is on the ions and their charges rather than the number of atoms of each element present. Therefore, calling it ‘disodium monosulfide’ would imply a covalent nature, which is misleading.
In summary, the correct name ‘sodium sulfide’ reflects the ionic character of the compound while adhering to standard nomenclature rules for ionic compounds.