Problem 49 - Chemistry The Central Science In Si Units

Question

Consider the molecule \(\mathrm{BF}_{3} .\) (a) What is the electron configuration of an isolated B atom? (b) What is the electron configuration of an isolated \(\mathrm{F}\) atom? (c) What hybrid orbitals should be constructed on the \(\mathrm{B}\) atom to make the \(\mathrm{B}-\mathrm{F}\) bonds in \(\mathrm{BF}_{3} ?(\mathbf{d})\) What valence orbitals, if any, remain unhybridized on the \(\mathrm{B}\) atom in \(\mathrm{BF}_{3}\) ?

Step-by-Step Solution

Answer

(a) B: 1s² 2s² 2p¹, (b) F: 1s² 2s² 2p⁵, (c) sp² hybridization, (d) one 2p orbital remains unhybridized.

Step 1: Electron Configuration of an Isolated B Atom

The element boron (B) has an atomic number of 5. This means it has 5 electrons. The electron configuration for a neutral boron atom is based on filling the orbitals in the order: 1s, 2s, 2p. Therefore, the electron configuration is 1s² 2s² 2p¹.

Step 2: Electron Configuration of an Isolated F Atom

Fluorine (F) has an atomic number of 9, which indicates it has 9 electrons. Following the same order of orbital filling, its electron configuration is 1s² 2s² 2p⁵.

Step 3: Hybrid Orbitals on B for B-F Bonds

In a  ext{BF}_3 molecule, boron undergoes hybridization to form three equivalent bonds. The most suitable hybridization for B in  ext{BF}_3 is sp². In sp² hybridization, the 2s and two of the 2p orbitals mix to form three equivalent sp² hybrid orbitals, which are oriented in a trigonal planar geometry to form  ext{B-F} sigma bonds.

Step 4: Unhybridized Orbitals on B Atom

After sp² hybridization in boron for  ext{BF}_3, one of the 2p orbitals remains unhybridized. This unhybridized 2p orbital is perpendicular to the plane formed by the three sp² hybrid orbitals and does not participate directly in bonding with fluorine atoms.

Key Concepts

Electron Configuration

Understanding electron configuration is fundamental in chemistry. It's the distribution of electrons in an atom's orbitals. Electrons fill orbitals in a specific order, following the principles of quantum mechanics. The Aufbau principle guides this, indicating that electrons occupy the lowest energy orbitals first. As they fill, we follow this sequence: 1s, 2s, 2p, 3s, and so on.

• Each orbital level has a set number of electrons it can hold:
• 1s can hold 2 electrons
• 2s can hold 2 electrons
• 2p can hold 6 electrons

These basics help us understand how atoms interact with each other to form molecules, like those in \( \text{BF}_3 \). Mastery of electron configuration forms the basis for understanding more complex concepts like hybridization.

Boron Atom

Boron, with atomic number 5, is a cornerstone of many chemical applications. Its electron configuration is written as 1s² 2s² 2p¹. This tells us that boron has:

• 2 electrons in the 1s orbital
• 2 electrons in the 2s orbital
• 1 electron in the 2p orbital

This configuration shows that boron has three electrons available for bonding. These electrons help it form compounds like boron trifluoride (\( \text{BF}_3 \)). The ability to combine and share these electrons through hybridization and bonding is what makes boron such a versatile element.

Fluorine Atom

Fluorine is highly electronegative, with an atomic number of 9. Its electron configuration is 1s² 2s² 2p⁵. This indicates:

• 2 electrons in the 1s orbital
• 2 electrons in the 2s orbital
• 5 electrons in the 2p orbitals

Due to this electron configuration, fluorine is eager to gain an electron to complete its p orbital. This tendency to attract electrons strongly defines its role in chemical reactions. It seeks to achieve a stable noble gas configuration similar to neon, which influences how it bonds with other elements, such as boron in \( \text{BF}_3 \).

sp² Hybrid Orbitals

In the molecule \( \text{BF}_3 \), boron undergoes an intriguing transformation through hybridization called sp² hybridization. This occurs when one 2s orbital and two 2p orbitals from boron mix to create three new equivalent orbitals known as sp² hybrid orbitals.
These orbits are crucial as they allow boron to form three equivalent \( \text{B-F} \) bonds distributed symmetrically in a trigonal planar shape. This orientation minimizes repulsion between electron pairs, fostering a stable molecular geometry. The creation of sp² hybrid orbitals is essential for the formation of stable compounds with predictable shapes and angles, which are vital for the structure and function of diverse molecules.

Unhybridized Orbitals

After hybridization, some orbitals in an atom may remain unhybridized, retaining their original state. In the case of \( \text{BF}_3 \), after the formation of sp² hybrid orbitals from boron, one of the 2p orbitals remains unhybridized.
These unhybridized p orbitals are important because they can be available for further chemical interactions, such as forming pi bonds, if needed. They are located perpendicular to the plane of the hybrid orbitals, maintaining a specific orientation that allows for potential overlap with other atoms' orbitals. Understanding unhybridized orbitals aids in visualizing molecular shapes and predicting reactivity patterns, which are critical for advanced concepts in physical and organic chemistry.