Question

Among the following compounds of boron, the species which also forms \(\pi\) -bond in addition to \(\sigma\) -bonds is (a) \(\mathrm{BF}_{3}\) (b) \(\mathrm{BF}_{4}^{-}\) (c) \(\mathrm{B}_{2} \mathrm{H}_{6}\) (d) \(\mathrm{BH}_{3}\)

Short answer

The compound is \(\mathrm{BF}_3\).

Step-by-step solution

Understand the Problem

The task is to determine which of the given boron compounds also forms \(\pi\)-bonds in addition to \(\sigma\)-bonds.

Review \(\sigma\) and \(\pi\) Bonds

\(\sigma\)-bonds are single bonds formed by the direct overlap of orbitals, while \(\pi\)-bonds are formed by the side-to-side overlap of orbitals and are typically found in double or triple bonds.

Analyze Each Compound

- **\(\mathrm{BF}_3\):** Trigonal planar structure where the boron atom forms three \(\sigma\)-bonds with fluorine atoms. The boron atom is electron deficient, allowing \(\pi\)-backbonding from fluorine's lone pairs into empty \((p)\)-orbital of boron, forming \(\pi\)-bonds.- **\(\mathrm{BF}_4^-\):** Tetrahedral structure with only \(\sigma\)-bonds, as all orbitals involved in bonding are utilized.- **\(\mathrm{B}_2\mathrm{H}_6\):** Contains two-electron three-center bonds known as banana bonds, without traditional \(\pi\)-bonding.- **\(\mathrm{BH}_3\):** Forms only \(\sigma\)-bonds; as it usually exists in the dimeric form \(\mathrm{B}_2\mathrm{H}_6\) to stabilize.

Identify the Compound with \(\pi\)-Bond Formation

From the analysis, \(\mathrm{BF}_3\) allows \(\pi\)-backbonding due to vacant \(p\)-orbital in boron and lone pairs in fluorine, resulting in \(\pi\)-bonding.

Key concepts

Pi bonds

Pi bonds, often represented by the Greek letter 'π', are fascinating chemical features. They form when two orbitals overlap sideways, rather than directly, which is different from sigma bonds that overlap end-to-end. These bonds are frequently observed in double or triple bonds. The sideways overlap allows for the sharing of electrons between atoms, which strengthens the bond after a sigma bond is already present. Because of their formation through the lateral overlap of p-orbitals, pi bonds are usually found in unsaturated compounds, such as alkenes and alkynes. This overlap restricts the rotation around the bond axis, imparting specific geometrical features to the molecules and contributing significantly to the chemical reactivity.

• Sideways overlap of orbitals
• Occurs in double and triple bonds
• Restricts rotation, impacting molecular geometry
• Common in unsaturated hydrocarbons

Sigma bonds

Sigma bonds, symbolized as 'σ' bonds, are the building blocks of molecular structure. They form when atomic orbitals overlap directly along the axis connecting two nuclei. This direct end-to-end overlap results in the strongest type of covalent bond, setting a strong foundation in molecular bonds. Because this overlap is the most efficient, sigma bonds are the first types of bonds to form between atoms. They allow for free rotation of bonded atoms, which is unlike pi bonds. Sigma bonds are pivotal in the structural integrity of a wide range of molecules, accounting for the primary bonding in single bonds across organic and inorganic chemistry.

• Formed by direct overlap of orbitals
• Single bonds in molecular structures
• Allows for free rotation
• Primary bond found in various molecules

BF3 molecule

The BF extsubscript{3} molecule, also known as boron trifluoride, plays an interesting role in chemistry due to its trigonal planar structure. In this molecular structure, boron sits in the center bonded to three fluorine atoms, resulting in the formation of three sigma bonds. Each of these bonds involves the overlap of the sp extsuperscript{2} hybrid orbitals of boron with the p-orbitals of the fluorine atoms. However, the boron atom in BF extsubscript{3} remains electron-deficient. Interestingly, due to the presence of vacant p-orbitals in boron, the fluorine atoms can donate their lone pair of electrons, forming an interesting phenomenon known as pi-backbonding. This interaction effectively forms pi bonds and gives the BF extsubscript{3} molecule some unique properties.

• Trigonal planar geometry
• Boron forms three sigma bonds with fluorine
• Electron-deficient boron permits pi-backbonding
• Unique molecular properties due to electron interaction

Chemical bonding

Chemical bonding is the mechanism by which atoms combine to form molecules, serving as the cornerstone of molecular chemistry. It dictates the structure, properties, and reactions of substances. Chemically, there are several types of bonds, with sigma and pi bonds being two fundamental types. Sigma bonds provide the basic framework through single direct overlaps of orbitals. Pi bonds, which form from the lateral overlap, supplement sigma bonds in double and triple bonds, lending stability to molecular structures. The concept of chemical bonding is crucial for understanding how compounds are created and how they behave under certain conditions. This understanding allows scientists and chemists to predict interactions and synthesize new materials.

• Core concept in molecular structure
• Comprises various types like sigma and pi bonds
• Dictates molecular properties and reactions
• Essential for new material synthesis and prediction