We perform first-principles calculations based on density functional theory and quasiparticle GW approximation to investigate the chemical trends in mechanical and electronic properties of twelve IV3V4 compounds (IV = C, Si, Ge, and Sn; V = N, P, and As). Our results indicate that these compounds are semiconductors, with the exception of C3P4 and C3As4. While Ge3P4 and Ge3As4 appear to be semimetals within local density approximation, but are, in fact, semiconductors with indirect band gaps, as revealed by GW calculations. We propose an empirical formula of band gaps for IV3V4 compounds that depends only on the nearest-neighbor distance and electronegativity difference. (C) 2010 Elsevier B. V. All rights reserved.