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Questions and Answers
Which compound is described as an ionic or saline hydride in the text?
Which compound is described as an ionic or saline hydride in the text?
Which type of hydride can be characterized by all the valence electrons of the central atom being involved in forming bonds?
Which type of hydride can be characterized by all the valence electrons of the central atom being involved in forming bonds?
In which type of hydride does not all the electrons on the central atom participate in bonding?
In which type of hydride does not all the electrons on the central atom participate in bonding?
What is the term used for a hydride that is not well characterized based on electron density and bonding?
What is the term used for a hydride that is not well characterized based on electron density and bonding?
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Which compound cannot be described using 2-centre 2-electron bonds due to electron deficiency?
Which compound cannot be described using 2-centre 2-electron bonds due to electron deficiency?
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In electron-deficient covalent hydrides, how is the bonding structure described?
In electron-deficient covalent hydrides, how is the bonding structure described?
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Which classification of hydrides includes binary compounds formed with beryllium and p-block elements?
Which classification of hydrides includes binary compounds formed with beryllium and p-block elements?
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In the context of hydrides, what element forms stronger bonds with period two elements compared to period three elements in the same group?
In the context of hydrides, what element forms stronger bonds with period two elements compared to period three elements in the same group?
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Which type of bond is considered among the strongest in chemistry, specifically involving hydrogen and other elements?
Which type of bond is considered among the strongest in chemistry, specifically involving hydrogen and other elements?
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In binary hydrides, what property is the key to understanding the differences in their chemistry?
In binary hydrides, what property is the key to understanding the differences in their chemistry?
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Which bond strength can be partially attributed to the ionic nature of H–N, H–O, H–F, and H–Cl bonds?
Which bond strength can be partially attributed to the ionic nature of H–N, H–O, H–F, and H–Cl bonds?
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Among which group of elements does hydrogen rank in its ability to form strong covalent bonds?
Among which group of elements does hydrogen rank in its ability to form strong covalent bonds?
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In the context of the text, what describes the electron distribution in beryllium hydride (BeH2)?
In the context of the text, what describes the electron distribution in beryllium hydride (BeH2)?
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What characteristic of beryllium cation (Be2+) affects its ability to form a lattice structure?
What characteristic of beryllium cation (Be2+) affects its ability to form a lattice structure?
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Which statement best describes the bonding in diborane based on the text?
Which statement best describes the bonding in diborane based on the text?
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How is the covalent bonding structure of beryllium hydride (BeH2) affected by its high electronegativity?
How is the covalent bonding structure of beryllium hydride (BeH2) affected by its high electronegativity?
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Which term best classifies a hydride where not all valence electrons of the central atom participate in bonding?
Which term best classifies a hydride where not all valence electrons of the central atom participate in bonding?
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What effect does the high charge density of beryllium cation (Be2+) have on its electropositivity?
What effect does the high charge density of beryllium cation (Be2+) have on its electropositivity?
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What is the main reason behind hydrogen's ability to form strong bonds with non-polar compounds?
What is the main reason behind hydrogen's ability to form strong bonds with non-polar compounds?
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In the breaking of an E-H bond where E is more electronegative than H, what kind of cleavage occurs?
In the breaking of an E-H bond where E is more electronegative than H, what kind of cleavage occurs?
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What type of bond cleavage occurs in compounds where E is less electronegative than H?
What type of bond cleavage occurs in compounds where E is less electronegative than H?
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How is the breaking of an E-H bond described when the electronegativity of E is approximately equal to that of H?
How is the breaking of an E-H bond described when the electronegativity of E is approximately equal to that of H?
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What happens if the central atom in a hydride participates in bonding using all its valence electrons?
What happens if the central atom in a hydride participates in bonding using all its valence electrons?
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Which statement best describes the classification of covalent hydrides based on electron distribution and bonding?
Which statement best describes the classification of covalent hydrides based on electron distribution and bonding?
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Study Notes
Oxidation States and Enthalpy
- Hydrogen exhibits an oxidation state of -1 in hydridic compounds and +1 when covalently bonded to more electronegative elements.
- Electron gain enthalpy for hydrogen is -73 kJ mol^-1.
- High ionization energy of hydrogen (+1312 kJ mol^-1) indicates it is difficult to form H⁺ ions.
Binary Hydrides
- Binary hydrides of Groups 1 and 2 are characterized as hydridic and primarily ionic solids.
- Ionic/Saline Hydrides (Groups 1 and 2): Salt-like, high-melting, white crystalline with significant ionic character.
- These hydrides adopt structures such as rock salt (for LiH to CsH), rutile structure (MgH₂), and PbCl₂ structure (CaH₂ – BaH₂).
- Formed through direct reaction with hydrogen at temperatures between 300 and 700°C.
Reactivity and Properties
- Ionic hydrides of Groups 1 and 2 are highly reactive, often stored in oil, and react with water to produce hydrogen gas and alkaline solutions.
- These hydrides act as good reducing agents, and their ionic character increases down the group.
- Reactivity of ionic hydrides also increases down the group.
Covalent Hydrides
- Formed via covalent bonds; includes a variety of compounds:
- Covalent hydrides of boron (e.g., B₂H₆, B₄H₁₀).
- Polymeric hydride of beryllium (BeH₂).
- Neutral binary compounds from Group 14 (e.g., CH₄).
- Basic compounds from Group 15 (e.g., NH₃, PH₃).
- Weakly acidic or amphoteric compounds from Group 16 (e.g., H₂O, H₂S).
- Strongly acidic compounds from Group 17 (e.g., HF, HI).
- Complex hydridic compounds like LiAlH₄ and NaBH₄.
Beryllium Hydride (BeH₂)
- Group 2 anomaly as it remains stable in water, unlike other Group 2 hydrides.
- In contrast, other Group 2 hydrides (e.g., CaH₂) react with water to release hydrogen gas and form alkaline solutions.
- BeH₂ features a 3D covalent polymeric structure and displays covalent characteristics due to its small and highly charged Be²⁺ cation.
- The structure involves bridging hydrogen atoms leading to 3-centre, 2-electron bonds.
Applications
- Calcium hydride acts as a drying agent for organic solvents such as acetonitrile (MeCN) and dichloromethane (CH₂Cl₂).
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Description
Test your knowledge on binary hydrides, oxidation states of hydrogen, and the properties of different hydrogen compounds. Explore concepts such as electron gain enthalpy, electronegativity, and the classification of hydrides as ionic or covalent.
