# Comparing covalent characters of two halides of group 15

Which is more covalent : NCl3 or PCl5 and why? This question was asked on a test, and the given answer was NCl3. Shouldn’t PCl5 be more covalent since pentahalides are more covalent than trihalides?

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Sep 2 '21 at 15:58

Pentahalides are more covalent than trihalides of the same element with the same halogen. For instance $$\ce{TaCl5}$$ is more covalent than $$\ce{TaCl3}$$ (the respective WP articles give their melting points as 216°C for the pentachloride and 440°C with decomposition for the trichloride); but we cannot make such a simple comparison of $$\ce{TaCl5}$$ with either $$\ce{TaBr3}$$ or $$\ce{PCl3}$$. Similarly the pentahalide/trihalide rule could be overriden by the difference between nitrogen and phosphorus in your case.