Determine the molecular geometry of SCl4
The Correct Answer and Explanation is:
The molecular geometry of sulfur tetrachloride (SCl₄) is seesaw.
Explanation
The geometry of SCl₄ can be determined by using the Valence Shell Electron Pair Repulsion (VSEPR) theory, which helps predict molecular shapes based on electron pair repulsions around a central atom. The central atom, sulfur (S), in SCl₄ has six valence electrons, while each chlorine (Cl) atom contributes one electron to form a single bond with sulfur. Thus, SCl₄ has a total of 10 electrons around the central sulfur atom, or five electron domains (pairs) in total.
Here’s how these electron pairs arrange themselves:
- Bonded Pairs: Sulfur forms single bonds with four chlorine atoms, which accounts for four bonding pairs of electrons.
- Lone Pair: One lone pair remains on the sulfur atom after bonding.
With five electron domains (four bonding pairs and one lone pair), the electron geometry around sulfur initially adopts a trigonal bipyramidal arrangement. This geometry is due to the repulsive forces between the electron pairs, which tend to maximize their separation around the central atom. In a trigonal bipyramidal arrangement:
- Three positions form a planar triangle around the central atom, known as equatorial positions.
- Two positions are perpendicular to this plane, known as axial positions.
In SCl₄, the lone pair of electrons occupies one of the equatorial positions because lone pairs exert more repulsive force than bonding pairs and therefore prefer a position with more space. With the lone pair in an equatorial position, the molecule takes on a seesaw shape rather than maintaining a perfectly symmetrical trigonal bipyramidal shape. This configuration minimizes repulsion and creates an asymmetrical shape that is distinctive for molecules with four bonded atoms and one lone pair.
Thus, the seesaw geometry of SCl₄ results from one lone pair and four bonded pairs around sulfur, leading to a non-symmetrical shape where one axial and three equatorial chlorine atoms surround sulfur, with bond angles close to 90° and 120° for stability.