Ch.9 - Molecular Geometry and Bonding Theories

Problem 105a

Chapter 9, Problem 105a

One of the molecular orbitals of the H2- ion is sketched below:

(a) Is the molecular orbital a s or p MO? Is it bonding or antibonding?

Verified step by step guidance

Step 1: Identify the type of atomic orbitals involved in the formation of the molecular orbital. In this case, the orbitals appear to be spherical, which suggests they are s orbitals.

Step 2: Determine if the molecular orbital is bonding or antibonding. Bonding orbitals result from constructive interference (overlap) of atomic orbitals, while antibonding orbitals result from destructive interference.

Step 3: Observe the phase of the orbitals. If the phases (shaded and unshaded regions) are the same in the region of overlap, it is a bonding orbital. If the phases are different, it is an antibonding orbital.

Step 4: Analyze the image provided. The molecular orbital shows a node (a region where the probability of finding an electron is zero) between the two nuclei, indicating destructive interference.

Step 5: Conclude that the molecular orbital is an antibonding orbital because of the presence of the node, and it is formed from s orbitals, making it a σ* (sigma star) antibonding orbital.

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Key Concepts

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

Molecular Orbitals (MOs)

Molecular orbitals are formed by the linear combination of atomic orbitals when atoms bond. They can be classified as bonding or antibonding. Bonding MOs have lower energy and increased electron density between the nuclei, while antibonding MOs have higher energy and a node between the nuclei, leading to decreased stability.

Bonding vs. Antibonding Orbitals

Bonding orbitals result from the constructive interference of atomic orbitals, allowing electrons to be shared between atoms, which stabilizes the molecule. In contrast, antibonding orbitals arise from destructive interference, where electron density is reduced between the nuclei, making the molecule less stable when occupied by electrons.

Types of Atomic Orbitals

Atomic orbitals are categorized into s, p, d, and f types, each with distinct shapes and energy levels. In diatomic molecules, the type of atomic orbitals involved in bonding determines the characteristics of the molecular orbitals formed. For example, s orbitals are spherical, while p orbitals have a dumbbell shape, influencing the orientation and overlap during bonding.

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Related Practice

Textbook Question

The structure of borazine, B₃N₃H₆, is a six-membered ring of alternating B and N atoms. There is one H atom bonded to each B and to each N atom. The molecule is planar. (a) Write a Lewis structure for borazine in which the formal charge on every atom is zero.

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Textbook Question

The structure of borazine, B₃N₃H₆, is a six-membered ring of alternating B and N atoms. There is one H atom bonded to each B and to each N atom. The molecule is planar. (e) What are the hybridizations at the B and N atoms in the Lewis structures from parts (a) and (b)? Would you expect the molecule to be planar for both Lewis structures? Would you expect the molecule to be planar for both Lewis structures?

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Textbook Question

The highest occupied molecular orbital of a molecule is abbreviated as the HOMO. The lowest unoccupied molecular orbital in a molecule is called the LUMO. Experimentally, one can measure the difference in energy between the HOMO and LUMO by taking the electronic absorption (UV-visible) spectrum of the molecule. Peaks in the electronic absorption spectrum can be labeled as p2p9p2p*, s2s9s2s*, and so on, corresponding to electrons being promoted from one orbital to another. The HOMO-LUMO transition corresponds to molecules going from their ground state to their first excited state. (c) The electronic absorption spectrum of the N2 molecule has the lowest energy peak at 170 nm. To what orbital transition does this correspond?

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Textbook Question

One of the molecular orbitals of the H2- ion is sketched below: (d) Compared to the H¬H bond in H2, the H¬H bond in H2- is expected to be which of the following: (i) Shorter and stronger, (ii) longer and stronger, (iii) shorter and weaker, (iv) longer and weaker, or (v) the same length and strength?

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Textbook Question

Place the following molecules and ions in order from smallest to largest bond order: N22+, He2+, Cl2 H2-, O22-.

Molecules that are brightly colored have a small energy gap between filled and empty electronic states (the HOMOLUMO gap; see Exercise 9.104). Suppose you have two samples, one is lycopene which is responsible for the red color in tomato, and the other is curcumin which is responsible for the yellow color in turmeric. Which one has the larger HOMO-LUMO gap?

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