Question

Which has the planar structure? (1) \(\mathrm{NH}_{4}{ }^{\prime}\) (2) \(\mathrm{SCl}_{4}\) (3) \(\mathrm{XeF}_{4}\) (4) \(\mathrm{BF}_{4}\)

Short answer

\text{XeF}_4 is planar due to its square planar molecular geometry.

Step-by-step solution

- Identify the molecular geometry

Determine the molecular geometry for each of the given compounds. Molecular geometry can be found using VSEPR theory. Analyzing molecular geometries will help identify which compound has a planar structure.

- Analyze \(\text{NH}_4^+\)

For \(\text{NH}_4^+\), nitrogen forms four single bonds with hydrogen. The molecular geometry is tetrahedral, which is not planar.

- Analyze \(\text{SCl}_4\)

For \(\text{SCl}_4\), sulfur is bonded to four chlorine atoms and has one lone pair. The resulting geometry is seesaw (a distorted tetrahedral), which is also not planar.

- Analyze \(\text{XeF}_4\)

For \(\text{XeF}_4\), xenon forms bonds with four fluorine atoms and has two lone pairs. This leads to a square planar molecular geometry, which is planar.

- Analyze \(\text{BF}_4^-\)

For \(\text{BF}_4^-\), boron forms four single bonds with fluorine. The resulting geometry is tetrahedral, which is not planar.

- Compare the geometries

From the analysis, \(\text{XeF}_4\) is the only molecule with a planar structure due to its square planar geometry.

Key concepts

VSEPR Theory

VSEPR (Valence Shell Electron Pair Repulsion) Theory helps us predict the shapes of molecules.

The idea is that electron pairs around a central atom will repel each other and try to get as far apart as possible.
These electron pairs can be bonding pairs (shared between atoms) or lone pairs (not shared).
The geometry of a molecule depends on the number of electron pairs around the central atom.
By understanding these repulsions, we can predict the 3D shape of molecules.

Molecular Geometry

Molecular Geometry refers to the 3D arrangement of atoms in a molecule.
This shape can affect the molecule's properties and its reactivity.
The arrangement is determined by the bonding pairs and lone pairs of electrons around the central atom.
For example:

• A molecule with four bonding pairs and no lone pairs has a tetrahedral geometry.
• A molecule with four bonding pairs and two lone pairs has a square planar geometry.

Knowing the molecular geometry helps in understanding how the molecule might interact with others.

Square Planar Geometry

In Square Planar Geometry, a central atom is surrounded by four atoms at the corners of a square.
This geometry is typically achieved when there are four bonding pairs and two lone pairs.
One classic example is \(\text{XeF}_4\), where Xenon has four fluorine atoms surrounding it, along with two lone pairs.
The pairs are positioned to minimize repulsion, resulting in a flat, square shape.
Square planar molecules are indeed planar and their flat surface could be crucial for reactions and interactions.

Tetrahedral Geometry

Tetrahedral Geometry has a central atom with four surrounding atoms forming the vertices of a tetrahedron.
It occurs when there are four bonding pairs and no lone pairs.
An angle of roughly 109.5 degrees is maintained between each pair to minimize repulsion.
Classic examples include \(\text{NH}_{4}^{+}\) and \(\text{BF}_4^{-}\).
Because of the 3D-spread, tetrahedral molecules are not planar.
The symmetrical form makes them stable and helps to understand their chemical behavior.