Textbook Question
Describe the structures of the white and red allotropes of phosphorus, and explain why white phosphorus is so reactive.
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Ch.22 - The Main Group Elements
McMurry8th EditionChemistryISBN: 9781292336145
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Table of contents
- Ch.1 - Chemical Tools: Experimentation & Measurement170
- Ch.2 - Atoms, Molecules & Ions160
- Ch.3 - Mass Relationships in Chemical Reactions169
- Ch.4 - Reactions in Aqueous Solution199
- Ch.5 - Periodicity & Electronic Structure of Atoms102
- Ch.6 - Ionic Compounds: Periodic Trends and Bonding Theory92
- Ch.7 - Covalent Bonding and Electron-Dot Structures61
- Ch.8 - Covalent Compounds: Bonding Theories and Molecular Structure59
- Ch.9 - Thermochemistry: Chemical Energy122
- Ch.10 - Gases: Their Properties & Behavior155
- Ch.11 - Liquids & Phase Changes54
- Ch.12 - Solids and Solid-State Materials73
- Ch.13 - Solutions & Their Properties120
- Ch.14 - Chemical Kinetics98
- Ch.15 - Chemical Equilibrium125
- Ch.16 - Aqueous Equilibria: Acids & Bases110
- Ch.17 - Applications of Aqueous Equilibria147
- Ch.18 - Thermodynamics: Entropy, Free Energy & Equilibrium86
- Ch.19 - Electrochemistry154
- Ch.20 - Nuclear Chemistry96
- Ch.21 - Transition Elements and Coordination Chemistry156
- Ch.22 - The Main Group Elements187
- Ch.23 - Organic and Biological Chemistry51
Chapter 22, Problem 22.86
Describe the structure of diborane (B2H6) and explain why the bridging B–H bonds are longer than the terminal B–H bonds.
Verified step by step guidance1
Diborane (B_2H_6) consists of two boron (B) atoms and six hydrogen (H) atoms. The structure is unique due to the presence of bridging hydrogen atoms.
In diborane, there are four terminal hydrogen atoms, each bonded to a boron atom, and two bridging hydrogen atoms that form bonds between the two boron atoms.
The terminal B–H bonds are typical covalent bonds, where each hydrogen shares a pair of electrons with a boron atom.
The bridging B–H bonds are different; they are three-center two-electron (3c-2e) bonds, involving two boron atoms and one hydrogen atom sharing two electrons.
The bridging B–H bonds are longer than the terminal B–H bonds because the electron density is spread over three atoms in the 3c-2e bonds, resulting in weaker and longer bonds compared to the typical two-center two-electron bonds of the terminal B–H.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Diborane Structure
Diborane (B2H6) has a unique structure characterized by two boron atoms and six hydrogen atoms. It features a central framework where two boron atoms are connected by two bridging hydrogen atoms, forming a 'banana bond' geometry. This arrangement leads to a three-dimensional shape that is not typical for simple covalent compounds, making diborane a fascinating example of electron-deficient bonding.
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Resonance Structures
Terminal vs. Bridging Bonds
In diborane, terminal B–H bonds are formed between a boron atom and a hydrogen atom directly attached to it, while bridging B–H bonds connect two boron atoms through a hydrogen atom. The terminal bonds are shorter due to the direct overlap of orbitals between boron and hydrogen, resulting in stronger, more stable bonds compared to the bridging bonds, which involve more complex orbital interactions.
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Bond Length and Strength
Bond length is influenced by the strength of the bond; stronger bonds tend to be shorter. In diborane, the terminal B–H bonds are stronger and thus shorter than the bridging B–H bonds. The bridging bonds are longer because they involve a different bonding interaction, where the hydrogen atom is shared between two boron atoms, leading to a weaker bond due to less effective orbital overlap.
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Related Practice
Textbook Question
Explain why the properties of boron differ so markedly from the properties of the other group 3A elements.
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Textbook Question
Which of the group 4A elements have allotropes with the diamond structure? Which have metallic allotropes? How does the variation in the structure of the group 4A elements illustrate how metallic character varies down a periodic group?
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Textbook Question
Compare and contrast the properties of ammonia and phosphine.
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Textbook Question
Using the shorthand notation of Figure 22.9, draw the structure of the cyclic silicate anion in which four SiO4 tetrahedra share O atoms to form an eight-membered ring of alternating Si and O atoms. Give the formula and charge of the anion.
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Textbook Question
Which of the following elements (X) will form a covalent hydride with the formula XH3 that is a gas at room temperature? (LO 22.4)
(a) Al (b) As (c) Ba (d) Se
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