Question: what is the electronegativity difference between nitrogen and fluorine in nf3?
Answer: The molecule has a trigonal pyramidal structure, like ammonia. The bond angle is reduced from 107° in ammonia to 101.9° in NF3, because the very electronegative fluorines pull the electrons in the N-F bonds towards themselves, reducing interelectronic repulsions, so that the NF3 'umbrella' closes up.