Question

Determine whether (a) \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\) and (b) \(\mathrm{XeF}_{4}\) are polar.

Short answer

(a) \(\mathrm{CH}_{2}\mathrm{Cl}_{2}\) is polar; (b) \(\mathrm{XeF}_{4}\) is nonpolar.

Step-by-step solution

Determine Lewis Structure for CH₂Cl₂

The first step is to determine the Lewis structure of \(\mathrm{CH}_{2}\mathrm{Cl}_{2}\), which has a carbon atom (C) bonded to two hydrogen atoms (H) and two chlorine atoms (Cl). The carbon atom is the central atom. Each chlorine forms a single bond with carbon, and each hydrogen forms a single bond with carbon. Carbon has no lone pairs, but each chlorine atom has three lone pairs.

Identify Molecular Geometry for CH₂Cl₂

The molecular geometry of \(\mathrm{CH}_{2}\mathrm{Cl}_{2}\) is tetrahedral because carbon, a group 14 element, is bonded to four atoms with no lone pairs on the central atom. This shape is characterized by bond angles of approximately 109.5 degrees.

Assess Polarity for CH₂Cl₂

The \(\mathrm{C-Cl}\) bonds are polar due to the difference in electronegativity between C and Cl, while \(\mathrm{C-H}\) bonds are relatively nonpolar. The asymmetric distribution of these \(\mathrm{C-Cl}\) bonds in the tetrahedral structure results in the overall molecule being polar, as the dipoles do not cancel each other.

Determine Lewis Structure for XeF₄

For \(\mathrm{XeF}_{4}\), the xenon atom (Xe) is the central atom surrounded by four fluorine atoms. Xe has two lone pairs. The fluorine atoms each form a single bond with xenon. Each fluorine has three lone pairs.

Identify Molecular Geometry for XeF₄

\(\mathrm{XeF}_{4}\) exhibits a square planar geometry. This is because, with two lone pairs on the xenon, the four fluorine atoms orient themselves in a square around the xenon to minimize electron pair repulsion, according to VSEPR theory.

Assess Polarity for XeF₄

In \(\mathrm{XeF}_{4}\), the fluorine atoms have a highly electronegative nature, creating polar bonds with xenon. However, because of the square planar geometry, the bond dipoles cancel each other out, making the overall molecule nonpolar.

Key concepts

Lewis Structure

Understanding the Lewis structure is fundamental in predicting the shape and behavior of molecules. For substances like \(\text{CH}_2\text{Cl}_2\), the Lewis structure reveals how atoms are bonded. Carbon acts as the central atom, bonding with two hydrogen atoms and two chlorine atoms. Each hydrogen atom connects with a single bond and does not possess any lone pairs. On the other hand, each chlorine atom also forms a single bond but carries three lone pairs.
In contrast, \(\text{XeF}_4\) has xenon as the central atom. This structure showcases xenon bonding with four fluorine atoms. The fluorines each form a single bond and have three lone pairs, similar to the chlorine in \(\text{CH}_2\text{Cl}_2\). Xenon, however, is unique as it includes two lone pairs, which heavily influences the molecule's geometry.

• Understanding which atom is central is crucial for mapping out the structure.
• Recognizing lone pairs helps predict the geometry and polarity of the molecule.
• The sharing of electrons via single bonds defines connectivity in these molecules.

By examining the Lewis structure, one can decipher the molecule's layout and prepare for deducing its geometry and polarity.

Molecular Geometry

The shape of a molecule, known as its molecular geometry, has profound effects on its properties. For \(\text{CH}_2\text{Cl}_2\), the molecular geometry is tetrahedral. Carbon, the central atom, connects symmetrically with four atoms—two hydrogen atoms and two chlorine atoms. Despite some difference in bond polarity, the structure remains consistent with this shape.
In the \(\text{XeF}_4\) molecule, the presence of two lone pairs on the xenon atom demands a different setup. This molecule displays a square planar geometry, where four fluorine atoms form a square around xenon, which minimizes electron pair repulsion. This arrangement directly affects the overall polarity.

• The shape influences how polar bonds are oriented and their ability to cancel out.
• All components, including lone pairs, play a vital role in determining the geometry.
• Each shape leads to distinct properties, affecting how molecules interact with one another.

Understanding molecular geometry gives us insights into the behavior of molecules and paints a clearer picture of their chemical nature.

VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) Theory is key to predicting molecular shapes. This theory states that electron pairs around a central atom will arrange themselves as far apart as possible to minimize repulsion.
For \(\text{CH}_2\text{Cl}_2\), VSEPR theory explains its tetrahedral shape, as there are no lone pairs on the carbon atom to disrupt the symmetry of the bonded hydrogen and chlorine atoms. This leads to bond angles of approximately 109.5 degrees.

In \(\text{XeF}_4\), VSEPR theory accounts for the square planar geometry. The two lone pairs on the xenon atom force the four fluorine atoms into a planar arrangement to reduce repulsive forces, resulting in 90-degree bond angles.

• VSEPR Theory is pivotal in accurately predicting molecular shape.
• Both bonded and lone electron pairs influence the final structure.
• The theory relies on minimizing repulsions between electron pairs.

Embracing VSEPR theory allows chemists to foresee and explain molecular shapes, aiding in understanding complex chemical interactions.