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11 Cards in this Set
- Front
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There are five main van der Waals forces and some important behaviors associated with them: |
London dispersion forces: Dipole-dipole forces: Dipole-ion forces: Dipole-induced dipole forces: Hydrogen bonding interactions: |
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London dispersion forces: |
resulting from the formation of instantaneous dipoles due to the motion ofelectrons in their orbitals. This force is present in all atoms, ions, and molecules but is only significant forneutral species that lack a permanent dipole and/or cannot hydrogen bond |
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Dipole-dipole forces: |
occur between all molecules possessing a permanent dipole. Related to thismolecular dipoles can induce neutral atoms and molecules to form instantaneous dipoles. In a given moleculethis force is stronger than the molecule's London dispersion forces and if the molecule can hydrogen bond aswell, it will be weaker than the hydrogen bonding interactions. |
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Dipole-ion forces: |
molecules possessing a dipole will also interact strongly with ions (monopoles) |
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.B(iii). Dipole-induced dipole forces: |
molecules which possess a permanent dipole can induce nonpolarmolecules to form an instantaneous dipole which will then interact with the permanent dipole of the firstmolecule. |
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C. Hydrogen bonding interactions: |
these are limited to a hydrogen atom (covalently bound to one of theatoms N, O, F) being weakly attracted to another N, O, F atoms, which itself has one or more H atomscovalently bonded to it. For a molecule, hydrogen bonding will be stronger than its dipole-dipole interactionsor London dispersion force interactions, if another hydrogen bonding molecule is available for interaction. |
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Why do the boiling points of the noble gases increase with mass? |
Larger atoms and molecules have larger polarizability therefore larger London dispersion forces. |
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Hydrogen Bonding in Water |
Hydrogen bonding in water results its unique properties such as its solid phase being less dense than its liquid phase. For almost all other substances, the solid form is more dense than the liquid form, resulting in the solid sinking in the liquid, while ice floats on water. Another unique property of water is its boiling temperature of 373 K (100 oC). |
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What is the primary reason the compounds NH3, H2O, and HF do not follow the general trend observed for the boiling points of the other Group 14-17 hydrides? |
NH3, H2O, and HF exhibit significant hydrogen bonding with other molecules of their own types. |
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What type(s) van der Waal force(s) should operate between the molecules of the Group 14 hydrides? |
London dispersion forces |
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Based on their bond polarity, molecular shape, and molecular dipole, which of the Group 14-17 hydrides should definitely be considered to exhibit dipole-dipole forces? (Exclude borderline cases |
H2Se PH3 H2O----- SbH3 H2S SnH4 H2Te AsH3 GeH4 NH3------ SiH4 CH4 HBr ----- HF ---- HCl----- HI |
