In comparison to CH 3 + in Assessment 2.82, the related molecule H 3 O + is not a Lewis acid at oxygen. Why?

All right. Hi everyone. So this question is asking us to provide a brief explanation as to why B three is a loic acid at boron. But the molecule NH three is not a luis acid at nitrogen. So here we have four different choices labeled A through D proposing different reasons as to why VH three is a low acid as opposed to NH three. Now, among these reasons include the mention of a lone pair, an empty P orbital and a double wand. So lets talk about it recall that a loic acid by definition is a chemical compound that can accept an electron pair. Now, examples of species that can accept electron pairs include hydrogen atoms connecting to electron elements because of the partially positive charge or positively charged metal ions. This is because positively charged species can accept negatively charged electron pairs. Now, by contrast, a low base is a chemical compound that can donate an electron pair. So while luis acids have to be electron deficient, in some way, lewis bases, by definition must be electron rich. So this includes compounds that have lone pairs on certain atoms as well as compounds that contain a negative charge. Now between bh three and NH three, the main difference is in the element at the center of the structure itself. For bh three, we have boron connecting to three hydrogen atoms. Now boron is found in group three A which means that it has three valence electrons. And also recall that boron is an exception to the octet rule in which it is neutral as opposed to positively charged with only six electrons around it. So even though according to the octet rule, boron is currently electron deficient, it's still going to remain neutral. Now, by contrast, we also have NH three which is nitrogen connecting to three hydrogen apps. But the difference here is that nitrogen belonging in group five A has five valence electrons, meaning that to fulfill the octet of nitrogen in NH three, it's going to have a lone pair of electrons in contrast to boron here. And so here lies the main difference between Bh three and NH three because boron, even though it is content with only six electrons, it still has an empty P orbital that could be filled, making it a luis acid. Now, by contrast, NH three is a low base because nitrogen has a long pair of electrons that it can donate and there you have it. So our answer here is going to be option B in the multiple choice. Bh three is a Luis acid because it has an empty P orbital, it can accept electrons, but NH three does not. And with that being said, thank you so very much for watching. And I hope you found this helpful.

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1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

3. Acids and Bases

Acids and Bases

Organic Chemistry

3. Acids and Bases

Acids and Bases

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Problem 83

Textbook Question

In comparison to CH₃⁺ in Assessment 2.82, the related molecule H₃O⁺ is not a Lewis acid at oxygen. Why?

Verified step by step guidance

Understand the concept of a Lewis acid: A Lewis acid is a species that can accept a pair of electrons to form a new covalent bond. In this case, we are analyzing whether H₃O⁺ (hydronium ion) can act as a Lewis acid at the oxygen atom.

Examine the electronic structure of H₃O⁺: The oxygen atom in H₃O⁺ is bonded to three hydrogen atoms and carries a formal positive charge. Oxygen typically has a lone pair of electrons, but in H₃O⁺, the positive charge indicates that the oxygen is already electron-deficient.

Compare H₃O⁺ to CH₃⁺: In CH₃⁺, the carbon atom has an empty p orbital, making it highly electrophilic and capable of accepting a pair of electrons. This is why CH₃⁺ is a strong Lewis acid. However, in H₃O⁺, the oxygen atom does not have an empty orbital available to accept electrons.

Consider the steric and electronic factors: The oxygen atom in H₃O⁺ is surrounded by three hydrogen atoms, and its lone pairs are already involved in bonding or are tightly held due to the positive charge. This makes it unlikely for the oxygen to act as a Lewis acid.

Conclude why H₃O⁺ is not a Lewis acid at oxygen: The lack of an empty orbital on oxygen and the electron-deficient nature of the molecule prevent H₃O⁺ from accepting a pair of electrons at the oxygen atom. Therefore, H₃O⁺ is not a Lewis acid at oxygen, unlike CH₃⁺, which has an empty orbital on carbon.

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Key Concepts

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

Lewis Acids and Bases

Lewis acids are defined as electron pair acceptors, while Lewis bases are electron pair donors. This theory expands the concept of acidity beyond protons (H⁺) to include any species that can accept an electron pair. Understanding this definition is crucial for analyzing the behavior of molecules like CH₃⁺ and H₃O⁺ in terms of their reactivity and interactions with other species.

Structure and Hybridization

The molecular structure and hybridization of atoms within a molecule significantly influence its chemical properties. In H₃O⁺, the oxygen atom is sp³ hybridized, leading to a tetrahedral geometry. This arrangement affects the availability of lone pairs on oxygen, which is essential for determining whether it can act as a Lewis acid or base.

Acidity and Protonation

Acidity in organic chemistry often involves the ability of a molecule to donate protons (H⁺). While H₃O⁺ is a strong acid due to its ability to donate protons, it does not act as a Lewis acid at oxygen because the oxygen atom is already fully satisfied with its bonding and lone pairs. This distinction is important for understanding the reactivity of H₃O⁺ compared to other cations like CH₃⁺.

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In comparison to CH3+ in Assessment 2.82, the related molecule H3O+ is not a Lewis acid at oxygen. Why?