Draw the molecular orbital picture of the following molecules and ions. In each, how many electrons are in the p orbital on the central atom? (b) BH₃

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Step 1: Begin by identifying the central atom in the molecule BH₃. In this case, the central atom is boron (B). Boron is in Group 13 of the periodic table and has three valence electrons.

Step 2: Determine the hybridization of the central atom. Boron in BH₃ forms three sigma bonds with hydrogen atoms. To achieve this, boron undergoes sp² hybridization, which involves mixing one s orbital and two p orbitals to form three sp² hybrid orbitals.

Step 3: Recognize that sp² hybridization leaves one unhybridized p orbital on boron. This unhybridized p orbital is perpendicular to the plane formed by the three sp² hybrid orbitals.

Step 4: Count the electrons in the unhybridized p orbital. Since BH₃ is a neutral molecule and boron does not have any lone pairs or additional electrons in the unhybridized p orbital, the p orbital on boron is empty (contains 0 electrons).

Step 5: Draw the molecular orbital picture. Represent the sp² hybrid orbitals forming sigma bonds with hydrogen atoms in a trigonal planar geometry. Show the unhybridized p orbital on boron as perpendicular to the plane, and indicate that it is empty (no electrons).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Molecular Orbital Theory

Molecular Orbital Theory describes how atomic orbitals combine to form molecular orbitals, which can be occupied by electrons. In this theory, electrons are delocalized over the entire molecule rather than being associated with individual atoms. Understanding this concept is crucial for visualizing the electron distribution in molecules like BH₃ and determining the occupancy of p orbitals.

Hybridization

Hybridization is the process by which atomic orbitals mix to form new hybrid orbitals that are suitable for the pairing of electrons to form chemical bonds. In the case of BH₃, the boron atom undergoes sp² hybridization, resulting in three equivalent sp² hybrid orbitals that form sigma bonds with hydrogen atoms, leaving the p orbital unoccupied.

Electron Configuration

Electron configuration refers to the distribution of electrons in an atom's orbitals. For boron in BH₃, the electron configuration is 1s² 2s² 2p¹, indicating that there are two electrons in the 1s orbital, two in the 2s orbital, and one in the 2p orbital. This configuration is essential for understanding how many electrons are present in the p orbital of the central atom.

Draw the molecular orbital picture of the following molecules and ions. In each, how many electrons are in the p orbital on the central atom? (b) BH3