Thionyl tetrafluoride (SOF4) is a colorless, reactive inorganic gas with a distorted trigonal bipyramidal molecular geometry. It is a polar molecule. The picture below shows its lewis structure.

Step 1: Construct the σ-bond framework

S is the central atom (Period 3; capable of an expanded octet; electronegativity lower than O and F)

Connect the framework: S bonds to one O atom and four F atoms

Optimal resonance form: One S=O double bond and four S?F single bonds

σ bonds: 5; plus one π bond within the S=O bond

Bonding electron count: 4 × (S–F single bonds) + S=O double bond

Number of shared electron pairs = 4 + 2 = 6; shared electrons = 12 e?

Step 2: Fill in lone pairs on peripheral atoms

O (double-bonded): Needs 2 lone pairs (4 e?) to satisfy the octet rule

Each F (single-bonded): 3 lone pairs (6 e?)

Lone pairs on 4 F atoms: 4 × 6 = 24 e?

Total peripheral lone pair electrons: 4 + 24 = 28 e?

Step 3: Account for electrons and determine lone pairs on central S

Electrons used: 12 (bonding) + 28 (peripheral lone pairs) = 40 e?

Step 4: Check for octet and expanded octet

Central S bonding: 4 single bonds + 1 double bond → Total of 10 valence electrons

S is in Period 3 and possesses empty 3d orbitals, allowing for an expanded octet structure.