Textbook Question
Suggest a plausible structure for the silicate anion in the mineral thortveitite, Sc2Si2O7.
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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 & Measurement143
- Ch.2 - Atoms, Molecules & Ions134
- Ch.3 - Mass Relationships in Chemical Reactions149
- Ch.4 - Reactions in Aqueous Solution157
- Ch.5 - Periodicity & Electronic Structure of Atoms92
- Ch.6 - Ionic Compounds: Periodic Trends and Bonding Theory73
- Ch.7 - Covalent Bonding and Electron-Dot Structures47
- Ch.8 - Covalent Compounds: Bonding Theories and Molecular Structure51
- Ch.9 - Thermochemistry: Chemical Energy104
- Ch.10 - Gases: Their Properties & Behavior138
- Ch.11 - Liquids & Phase Changes43
- Ch.12 - Solids and Solid-State Materials56
- Ch.13 - Solutions & Their Properties98
- Ch.14 - Chemical Kinetics79
- Ch.15 - Chemical Equilibrium107
- Ch.16 - Aqueous Equilibria: Acids & Bases94
- Ch.17 - Applications of Aqueous Equilibria125
- Ch.18 - Thermodynamics: Entropy, Free Energy & Equilibrium66
- Ch.19 - Electrochemistry130
- Ch.20 - Nuclear Chemistry73
- Ch.21 - Transition Elements and Coordination Chemistry122
- Ch.22 - The Main Group Elements155
- Ch.23 - Organic and Biological Chemistry43
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
Look at the location of elements A, B, C, and D in the following periodic table:
(d) Which hydrides react with water to give an acidic solution, and which give a basic solution?
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Textbook Question
Why are CO and CN– so toxic to humans?
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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
Arrange the following oxides in order of increasing basic character: Al2O3, Cs2O, K2O, N2O5.
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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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