Step 1: Sulfur (EN = 2.5) is less electronegative than fluorine (EN = 4) so sulfur is the central atom.
Step 2: The total number of valence electrons present in SF4 is:
Group Valence Electrons
S 6A 1 × 6 e– = 6 e–
F 7A 4 × 7 e– = 28 e–
Total: 34 valence e–
Step 3: Sulfur follows an expanded octet to form 4 bonds while halogens, when not the central atom, form only 1 bond. The Lewis structure is:
Step 4: The electronegativity difference between S and F is 0.5 so the S–F bond is polar. Recall that dipole arrows point towards the more electronegative atom.
Drawing the dipole arrows:
Which one of the following molecules/ions is nonpolar?