To determine the geometric shape of sulfur tetrafluoride (SF₄) using the VSEPR (Valence Shell Electron Pair Repulsion) model, we follow these steps:
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Count the Valence Electrons: Sulfur (S) has 6 valence electrons, and each fluorine (F) has 7 valence electrons. Therefore, for SF₄:
- Sulfur: 6 electrons
- 4 Fluorines: 4 × 7 = 28 electrons
- Total = 6 + 28 = 34 valence electrons.
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Determine the Central Atom: Sulfur, being less electronegative than fluorine, will be the central atom.
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Write the Lewis Structure: In the Lewis structure, sulfur is surrounded by 4 fluorine atoms, each bonded to sulfur by a single bond (taking 8 electrons). That leaves 2 electrons on the sulfur atom, leading to one lone pair of electrons.
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Determine Electron Geometry: The molecular geometry is influenced by both bonded atoms and lone pairs. In SF₄, there are 4 bonded pairs (to fluorine) and 1 lone pair on the sulfur atom.
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Predict the Molecular Geometry: According to VSEPR theory, the presence of a lone pair distorts the geometry. With 4 bonded atoms and 1 lone pair, the geometry is classified as "seesaw".
Thus, the geometric shape that best describes SF₄ is seesaw.