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Sulfur tetrafluoride (SF₄) Lewis structure

34 valence electrons, see-saw

S F F F F
SF₄ as the Lewis Structure Generator draws it: lone pairs as dots.

Build SF₄ step by step in the Lewis Structure Generator

What is the Lewis structure of SF₄?

Sulfur tetrafluoride, SF₄, has 34 valence electrons. Sulfur is the central atom, joined by four S−F single bonds. It carries one lone pair on the central S and three on each F. Every formal charge is zero. S is AX₄E₁: see-saw, with ideal bond angles of 90°, 120° and 180°, and the molecule is polar.

Valence electrons in SF₄

Element Group Valence electrons Atoms Electrons
Sulfur 16 6 1 6
Fluorine 17 7 4 28
Total 34

In one line: 6 + 4 × 7 = 34. Each atom brings the valence electrons its group gives it.

How to draw the SF₄ Lewis structure

  1. Count the valence electrons. Valence electrons: S 6 and each F 7. 6 + 4 × 7 = 34.
  2. Choose the central atom. S goes in the middle: S is the least electronegative atom other than H, χ 2.58 against 3.98 for F.
  3. Join the atoms with single bonds. Four single bonds use 8 electrons, leaving 34 − 8 = 26.
  4. Complete the outer atoms. Each outer atom takes enough lone pairs to reach eight: 4 F × 6 = 24, leaving 26 − 24 = 2.
  5. Put the rest on the central atom. The 2 left go on the central atom as one lone pair on S, and S now has 10 electrons round it. That is more than eight, which an atom from period 3 on can hold.
  6. Make multiple bonds where needed. Every atom already has an octet or more, so no lone pair needs to become a bond.

Lone pairs and formal charges in SF₄

Atom Number Bonds Lone pairs Electrons round it Formal charge, V − N − B/2
S (central) 1 four single bonds 1 10 6 − 2 − 4 = 0
F 4 one single bond 3 8 7 − 6 − 1 = 0

V is the atom’s valence electrons, N its nonbonding electrons and B its bonding electrons. The formal charges add up to 0, the molecule’s overall charge.

Shape and polarity of SF₄

Central atom S
VSEPR class AX₄E₁
Electron geometry trigonal bipyramidal
Molecular geometry see-saw
Ideal bond angles 90°, 120° and 180°
Measured bond angle 102°
Polarity, an estimate polar

The see-saw shape leaves the bond dipoles unbalanced.

S has four σ bonds and one lone pair, five electron domains in all, so its electron geometry is trigonal bipyramidal. Counting only the bonded atoms, the molecular geometry is see-saw.

The VSEPR Molecular Geometry viewer turns the AX₄E₁ shape in 3D, lone pairs included.

The measured angle is the accepted experimental value the VSEPR viewer quotes for this molecule.

Work with SF₄