Hi there. I have to determine the Lewis structure for NSF. So first I thought of something like this: N=S-F, with the nitrogen with four free electrons, the sulfur with two, and the fluorine with six. The formal charges gives -1 for Nitrogen, +1 For sulfur, and 0 for Fluorine. But the octet rule is accomplished. The sulfur, which has the lowest electronegativity it's central, as is proposed by the general rule. Then I thought of this: S=N-F With this configuration S has four free electrons, N two, and F 6 again. Formal charges now are zero, but now the sulfur is a terminal atom, so I don't have the lowest electronegativity at the center. Then I looked for this at the internet, and found that the actual formula is: N≡S-F With this configuration formal charges again gives zero. But the octet rule is not accomplished. Now I know this must be the real formula. But what law should I follow when I have options like this? should I always use the expanded octet in this cases?