Which one of the following has the highest ionic character? (a) BeF3 (b) SiO2 (c) NCl3 (d) K2S

The ionic character of a chemical bond is determined by the electronegativity difference between the constituent atoms. According to Fajan's rules and electronegativity trends, bonds between highly electropositive metals (Group 1) and non-metals exhibit the highest ionic character. Potassium (K) is a Group 1 alkali metal with very low electronegativity, while Sulfur (S) is a non-metal; their combination in K2S results in a significant electronegativity difference, making it a binary ionic compound. In contrast, BeF2 (often miswritten as BeF3 in the prompt) has significant covalent character due to the high charge density of the small Be2+ cation. SiO2 and NCl3 are primarily covalent compounds [1]. Silicon and Nitrogen are non-metals/metalloids that share electrons rather than undergoing complete charge transfer. Therefore, K2S possesses the highest ionic character among the given options.

Sources

1. [1] https://dn790008.ca.archive.org/0/items/chem-7-zumdahl/Zumdahl_Text.pdf