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What is the ideal composition of noble gas hydrates formed by gases like Ar, Kr, and Xe?
What is the ideal composition of noble gas hydrates formed by gases like Ar, Kr, and Xe?
XeF4 is known to act as a donor of F− ions.
XeF4 is known to act as a donor of F− ions.
False
What type of interactions hold the lattice of quinol together?
What type of interactions hold the lattice of quinol together?
Hydrogen bonds
Noble gas hydrates are not formed by ______ or ______.
Noble gas hydrates are not formed by ______ or ______.
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Match the following xenon fluorides with their properties:
Match the following xenon fluorides with their properties:
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What happens to clathrates when they undergo dissolution or melting?
What happens to clathrates when they undergo dissolution or melting?
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The conventional valence bond theory is sufficient to explain the structures of xenon fluorides.
The conventional valence bond theory is sufficient to explain the structures of xenon fluorides.
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What type of structure is indicated by the vibrational spectrum of XeF6 in the vapor state?
What type of structure is indicated by the vibrational spectrum of XeF6 in the vapor state?
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Which of the following noble gases is the second most abundant element in the Universe?
Which of the following noble gases is the second most abundant element in the Universe?
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All noble gases occur in the Earth's atmosphere.
All noble gases occur in the Earth's atmosphere.
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What is the main energy source for the Sun?
What is the main energy source for the Sun?
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The ___ of helium from the Sun was first detected spectroscopically.
The ___ of helium from the Sun was first detected spectroscopically.
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What pressure is typically used to obtain clathrates of quinol in the presence of noble gases?
What pressure is typically used to obtain clathrates of quinol in the presence of noble gases?
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Match the noble gases with their unique traits:
Match the noble gases with their unique traits:
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Xenon is used in some types of fluorescent lights and certain medical imaging applications.
Xenon is used in some types of fluorescent lights and certain medical imaging applications.
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What are B2H6 molecules commonly bonded with?
What are B2H6 molecules commonly bonded with?
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What is a characteristic feature of boron in terms of its electron configuration?
What is a characteristic feature of boron in terms of its electron configuration?
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Boron can form metallic bonds due to its small size and higher ionization energy.
Boron can form metallic bonds due to its small size and higher ionization energy.
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What is the dimerization product of BH3?
What is the dimerization product of BH3?
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The structure of diborane (B2H6) features bridging hydrogen atoms that are attached to __________ boron atoms.
The structure of diborane (B2H6) features bridging hydrogen atoms that are attached to __________ boron atoms.
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Match the properties with the correct boron allotropes:
Match the properties with the correct boron allotropes:
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How many valence electrons does diborane (B2H6) possess?
How many valence electrons does diborane (B2H6) possess?
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In diborane, all BH bond distances are identical.
In diborane, all BH bond distances are identical.
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How many vertices does the icosahedral B12 unit contain?
How many vertices does the icosahedral B12 unit contain?
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Study Notes
Boron - Nonmetal - Electron Deficient
- Boron exists in several allotropes.
- Solid phases' crystal structures utilize the icosahedral B₁₂ unit (20-faced) as a recurring motif in boron chemistry.
- This unit has 12 vertices, 20 triangular faces, and 30 edges.
- Amorphous boron is a brown powder, while crystalline boron forms shiny black crystals.
Boron Bonding
- Boron is unique among elements due to having fewer electrons (1s², 2s² 2p¹) than atomic orbitals available for bonding.
- It forms covalent bonds (no metallic bonds) due to its small size and high ionization energy.
- This structural complexity leads to allotropic modifications and several allotropes.
Boron Hydrides - Diborane
- Diborane, B₂H₆ (diborane(6)), is a boron hydride.
- B atoms are typically attached to more than 3 atoms, and bridging hydrogen atoms are frequently present.
- Bonding in boron hydrides is not easily described using VB theory.
- The structure of B₂H₆ (D₂h symmetry) is shown in Figure 5.31.
- Key features: bridging H atoms are attached to two B atoms, each B atom is bonded to four H atoms, and BH bond lengths vary, suggesting different bonding types.
- B₂H₆ is described as electron-deficient. It's a dimer of BH₃ and possesses 12 valence electrons.
Structure of Diborane
- The formation of B-H-B bridges is depicted as in diagram 5.10.
- Terminal BH interactions are considered 2c-2e bonds.
- Bridging units are treated as 3c-2e bonding interactions.
- The 3c-2e interaction in half is expected to be weaker than a terminal 2c-2e bond (consistent with observed bond lengths)
Molecular Orbital (MO) of Diborane
- MO treatment provides insight into electron density distribution in diborane (B₂H₆).
- Using ligand group orbital approach, interactions between bridging H atoms and the B₂H₄ fragment can be considered, as seen in Figures below.
- The structure of B₂H₆ is broken down into H₂B-BH₂ and H-H fragments.
- The ligand group orbitals (LGOs) for the H-H fragment are considered.
- Six lowest-energy LGOs for the B₂H₄ unit, with nodal planes in the b₂u orbitals are examined.
- An important MO model conclusion is that boron-hydrogen bridge character is delocalized across all four bridging atoms within B₂H₆.
- Two of the MOs involve four electrons each. This is consistent with the 3c-2e B-H-B model.
- Terminal B-H bonds and bridging B-H-B bonds each contain two electrons.
Xenon Fluorides
- Xenon fluorides are synthesized by reacting xenon elements directly, usually within a nickel reaction vessel.
- The vessel is passivated with F₂ forming a NiF₂ coating to remove surface oxides, which react with xenon fluorides.
- Formation of higher fluorides is favored using higher fluorine proportions and higher total pressure. Key reactions outlined.
- All xenon fluorides sublime readily in a vacuum and readily decompose with water, with XeF2 exhibiting the slowest decomposition.
- XeF₄, and XeF₆ decompose rapidly.
- XeF₆, XeF₄, and XeF₂ reacts with other substances in specified reactions.
- [XeF₅]⁻ ion is one of two known pentagonal planar species, the other being [IF₅]²⁻.
Structures of Xenon Halides (VSEPR Model)
- Xenon halide structures cannot be explained by conventional valence bond theory.
- This theory assumes octet acquisition by elements, but noble gases already have octet configurations.
- Xenon compound structures are considered hypervalent compounds where valence electron counts are even number greater than 8.
- The vapor state vibrational spectrum of XeF₆ shows an octahedron distorted by an active lone pair in a centered face.
- XeF₆ molecules may theoretically have an octahedral structure (where the lone pair is in the inactive s-orbital) or a distorted octahedral structure (where the lone pair is active).
- In fact, XeF₆ exhibits fluxionality in gas phase. It exchanges between structures where the lone pair passes through an F₃ triangle (one octahedral face) of the distorted octahedral XeF₆ molecule.
Assignment Questions
- Nuclear fission/fusion: Notes required.
- Solubility product/common ion effect: Explanation needed.
- Xenon fluorides' structure: Explanation for why conventional valence bond theory fails is needed.
- MO diagram of XeF₂: 3c-2e bond explanation necessary.
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Description
This quiz focuses on the unique properties and structures of boron, including its allotropes and bonding characteristics. Learn about boron hydrides like diborane and the complexity of its covalent bonds. Test your knowledge on these intriguing aspects of boron chemistry.
