Question

Among the following compounds, the one that is polar and has the central atom with sp2 hybridization is: (a) \(\mathrm{H}_{2} \mathrm{CO}_{3}\) (b) \(\mathrm{SiF}_{4}\) (c) \(\mathrm{BF}_{3}\) (d) \(\mathrm{HClO}_{2}\)

Short answer

The compound \(\mathrm{HClO}_{2}\) is polar and has \( sp^2 \) hybridization.

Step-by-step solution

Identify Hybridization

To determine if the compound has a central atom with \( sp^2 \) hybridization, check for a central atom that is bonded to three groups. \( sp^2 \) hybridization typically results when the central atom forms three \( \sigma \) bonds and may include \( \pi \) bonds for double bonds. Check each compound.

Analyze Compound (a): \(\mathrm{H}_2 \mathrm{CO}_3\)

\(\mathrm{H}_2 \mathrm{CO}_3\) is carbonic acid. Its central carbon atom is bonded to two \(\mathrm{OH}\) groups and one \(\mathrm{O}\) atom using double bonds. Carbon is \( sp^2 \) hybridized as it forms three \( \sigma \) bonds: two to \( \mathrm{OH} \) and one to \( \mathrm{O} \).

Analyze Compound (b): \(\mathrm{SiF}_4\)

\(\mathrm{SiF}_4\) is silicon tetrafluoride, with silicon as the central atom surrounded by four \(\mathrm{F}\) atoms in a tetrahedral arrangement. This involves \( sp^3 \) hybridization, not \( sp^2 \).

Analyze Compound (c): \(\mathrm{BF}_3\)

\(\mathrm{BF}_3\) is boron trifluoride. The boron atom is the central atom, bonded to three \(\mathrm{F}\) atoms in a planar triangular shape. This features \( sp^2 \) hybridization, but the molecule is nonpolar due to symmetric charge distribution.

Analyze Compound (d): \(\mathrm{HClO}_2\)

In \(\mathrm{HClO}_2\), chlorine is the central atom, connected with \(\mathrm{OH}\) and \(\mathrm{O}\) and an additional \(\mathrm{O}\) with a single bond. This generally results in \( sp^2 \) hybridization. The different electronegativities in \(\mathrm{HClO}_2\) lead to a polar molecule due to unsymmetrical charge distribution.

Determine Polarity and Hybridization

Verify that \(\mathrm{HClO}_2\) exhibits \( sp^2 \) hybridization with chlorine as the central atom bonded to different atoms, causing a polar molecule due to varying dipole moments which do not cancel.

Key concepts

sp2 Hybridization

In chemistry, hybridization is a concept that helps explain the structure of molecules. It refers to the mixing of atomic orbitals to form new hybrid orbitals for bonding.

sp2 hybridization occurs when one s orbital and two p orbitals from the same atom mix together. This results in three equivalent sp2 hybrid orbitals. Typically, this type of hybridization is observed in atoms that form three sigma (σ) bonds.

Examples of compounds exhibiting sp2 hybridization include carbon in carbonic acid ( H₂CO₃), where it forms a structure with two OH groups and an additional double-bonded oxygen, and boron in boron trifluoride ( BF₃) where the boron atom is connected to three fluorine atoms. The hybrid orbitals arrange themselves in a trigonal planar shape, which is why compounds like BF₃ appear flat and triangular.

Each compound behaves differently based on the other atoms present and their electron characteristics. For instance, although BF₃ exhibits sp2 hybridization, its geometry makes it non-polar due to the symmetry of the fluorine atoms around the boron.

Polarity in Molecules

Polarity in molecules is an essential concept in chemistry, determining how molecules interact with each other. A molecule is considered polar when there is an uneven distribution of electrons between its atoms, leading to a molecule having a positive end and a negative end.

This phenomenon occurs due to differences in electronegativity among the atoms within a molecule. Electronegativity is a measure of how strongly atoms attract bonding electrons. When bonded atoms have a significant difference in electronegativity, dipole moments arise, making the molecule polar.

A good example is hydrochlorous acid ( HClO₂), where chlorine as the central atom forms bonds with oxygen and hydroxyl (OH) groups. The differing electronegativities within this molecule result in an asymmetrical shape. This asymmetrical shape and charge distribution mean that HClO₂ is polar. The unshared electron pairs on oxygen add to the asymmetrical charge distribution, enhancing polarity.

Polarity affects many properties of the molecule, such as its solubility in water—since water is a polar molecule—as well as its melting and boiling points.

Molecular Geometry

Molecular geometry is the 3-D arrangement of atoms within a molecule, which significantly influences the molecule's physical and chemical properties. This geometry is determined by the hybridization of atoms and the repulsions between electron pairs around the central atom.

For instance, in boron trifluoride ( BF₃), the boron atom is in the center, with fluorine atoms forming a trigonal planar shape. This formation arises due to the sp2 hybridization of boron, resulting in three equally spaced regions of electron density. In contrast, SiF₄ (silicon tetrafluoride) doesn't exhibit sp2 hybridization—instead, it has sp3 hybridization leading to a tetrahedral shape due to four bonded fluorine atoms.

The geometry of a molecule like HClO₂ isn't as straightforward. Mixed types of bonds and the lone pairs of electrons on the oxygen atoms contribute to its bent shape. This unsymmetrical geometry results in a polar molecule since the bond dipoles do not cancel each other out.

Understanding molecular geometry allows chemists to predict the behavior of molecules in various environments and reactions. It is crucial for predicting molecular polarity, reactivity, and interaction with other molecules.