Question

Mow many substituents surround the sulfur atom in \(\mathrm{SF}_{4}\) ?

Short answer

There are 4 substituents around the sulfur atom in \(SF_{4}\).

Step-by-step solution

Determine the Valence Electrons

Sulfur (\(S\)) is in group 16 on the periodic table and has 6 valence electrons. Each fluorine (\(F\)) atom has 7 valence electrons, but as substituents, only the ones from sulfur count for determining geometry.

Use VSEPR Theory

The \(SF_{4}\) molecule has 4 fluorine atoms bonded to sulfur and one lone pair. According to VSEPR (Valence Shell Electron Pair Repulsion) Theory, these regions seek to be as far apart as possible.

Identify Molecular Geometry

With 4 bonded atoms and 1 lone pair, \(SF_{4}\) is classified as having a 'see-saw' shape. This means there are 4 substituents (fluorine atoms) around the sulfur atom.

Count Substituents

The substituents that actively surround the sulfur atom in \(SF_{4}\) are the 4 fluorine atoms. The lone pair is not considered a substituent in this context.

Key concepts

Valence Electrons

Valence electrons are the outermost electrons of an atom and are crucial in determining how the atom will bond with other atoms. These electrons are involved in forming chemical bonds and help dictate the geometry of a molecule. For example, sulfur ( S ), located in group 16 of the periodic table, has 6 valence electrons. This information is essential when predicting or explaining the bonding patterns and molecular shapes of compounds like sulfur tetrafluoride ( SF_{4} ).
Understanding valence electrons helps us predict the number and type of bonds an atom can form. In SF_{4} , each fluorine ( F ) atom contributes one valence electron to form a bond with sulfur. However, when dealing with molecular geometry, primarily the valence electrons of the central atom (sulfur in this case) are considered.

VSEPR Theory

VSEPR Theory, or Valence Shell Electron Pair Repulsion Theory, is a model used to determine molecular geometry. This theory proposes that electron pairs around a central atom tend to arrange themselves as far apart as possible due to electron pair repulsion. This model helps to minimize repulsion and thus dictates the geometry of the molecule. In the case of SF_{4} , VSEPR theory helps to explain why the molecule takes on a 'see-saw' shape.
According to VSEPR, the number of bonding pairs (between sulfur and fluorine) and lone pairs must be considered. With 4 bonds and one lone pair around sulfur, the VSEPR theory provides a way to visualize this arrangement as it adopts a geometry that minimizes repulsion.

Substituents

In molecular geometry, substituents refer to atoms or groups directly attached to a central atom. They are integral to determining the shape of a molecule. In the molecule SF_{4} , the substituents surrounding sulfur are the four fluorine atoms. These atoms directly interact with the central sulfur atom and dictate the molecule's geometry.
A crucial part of this concept is understanding that only the bonds formed with the central atom count toward the geometry as 'substituents.' The lone pair on sulfur, while affecting the geometry, is not counted as a substituent. Therefore, in SF_{4} , there are exactly four substituents.

Lone Pair

A lone pair refers to a pair of valence electrons that are not shared with another atom, hence not involved in bonding. These unshared electrons can significantly affect the shape of a molecule even though they aren't considered substituents. For sulfur in SF_{4} , one of these pairs exists as a lone pair.
Lone pairs occupy space and exert repulsion similar to bonding pairs, thus altering the overall geometry of the molecule. In SF_{4} , the lone pair creates an asymmetry that results in the molecular 'see-saw' shape. This concept emphasizes how lone pairs must be factored into the prediction of molecular geometry.