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DesLee26
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The polarity of an individual bond is measured as its __, defined as (state formula), where δ is the __ and d is the __
- bond dipole moment (u)
- u= δ x damount of charge at either end of hte dipole
- distance between the charges
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Dipole moments are expressed in units of the __.
debye
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A simple rule of thumb, using common units, is that __
u (debyes)= 4.8 x δ (electron charge) x d (in angstroms)
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Bond dipole moments in organic compounds range from __ in symmetrical bonds to about __ for the strongly polar triple bond.
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A __ is the dipole moment of the molecule taken as a whole.
molecular dipole moment
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Molecular dipole moments can be measured __, in contrast to __, which must be estimated by comparing various compounds. The value of hte molecular dipole moment is equal to the __. This __ sum reflects both the __ and the __ of each individual bond dipole moment.
- directly
- bond dipole moments
- vector sum of hte individual bond dipole moments
- vector
- magnitude
- direction
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Lone pairs of electrons contribute to hte __. Each lone pair corresponds to a __, wth the __ having a __ balanced by a __ of the __.
- dipole moments of bonds and molecules
- charge separation
- nucleus
- partial positive charge
- negative charge
- lone pair
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When two molecules approach, what do they do?
attract or repel each other
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In general, the forces are __ until the molecules come so close that they __ on each other's __.
- attractive
- infringe
- van der Waals radius
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When infringement happens, the small attractive force quickly becomes a large __, and the molecules __.
- repulsive force
- bounce off each other
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Three major kinds of attractive forces cause molecules to associate into solids and liquids:
- 1) dipole dipole forces of polar molecules
- 2) London dispersion forces that affect all molecules
- 3) hydrogen bonds tha tlink molecuels having --OH or --NH groups
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Most molecuels have __ as a result of their __. Each molecular dipole moment has a __ and a __. The most stable arrangement has the __ of one dipole close to the __ of another.
- permanent dipole moments
- polar bonds
- positive end
- negative end
- positive end
- negative end
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When two negative ends or two positive ends approach each other, they ___, but they may __ .
- repel
- turn and orient themselves in the more stable positive to negative arrangement
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__ are generally attractive intermolecular forces resulting from the attraction of hte positive and negative ends of hte dipole moments of polar molecules.
dipole-dipole forces
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Polar molecules are mostly oriented int he __ arrangement, and the net force is __. This attraction must be overcome when the liquid __, resulting in larger __ and higher __ for strongly polar compounds.
- lower-energy positive to negative arrangment
- attractive
- vaporizes
- heats of vaporization
- boiling points
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In nonpolar molecules, sucha s carbon tetrachloride, the principal attractive force is the __, one of the __.
- London dispersion force
- van der Waals forces
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The London force arises from __
temporary dipole moments that are induced in a molecule by other nearby molecules
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A small __ moment is induced when one molecule approaches another molecule in which the electrons are slightly displaced from a __. The electrons in the approaching molecule are __ slightly so that an attractive __ results.
- temporary dipole moment
- symmetrical arrangement
- displaced
- dipole-dipole interaction
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The temporary dipoles last how long?
Are they static?
- a fraction of a second
- no they constantly change; they they are correlated so their net force is attractive
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What does the attractive force depend on?
close surface contact of two molecuels, so it is roughly proportional to the molecular surface area
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A hydrogen bond is __, but a __. A hydrogen atom can participate in __ if it is bonded to __, __ or __.
- not a true bond
- particularly strong dipole-dipole attraction
- hydrogen bonding
- oxygen
- nitrogen
- fluorine
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Organic compounds do not contain __ bonds, so we consider __ and __ hydrogens to be hydrogen bonded.
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The OH and NH bonds are strongly __, leaving the hydrogen with a __. This __ hydrogen has a strong affinity for __, and it forms intermolecular attachments with teh __ on oxygen or nitrogen atoms
- polarized
- partial positive charge
- electrophilic
- nonbonding electrons
- nonbonding electrons on
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True or False:
Amines form stronger hydrogen bonds than alcohols, because oxygen is more electronegative than nitrogen.
- True or False:
- Amines form stronger hydrogen bonds than alcohols, because oxygen is more electronegative than nitrogen.
- Alcohols form stronger hydrogen bonds than amines...
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In addition to affecting boiling and melting points, intermolecular forces determine the __ properties of organic compounds.
solubility
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The general rule is ?
- like dissolves like
- polar dissolves polarnonpolar dissolves nonpolar
- etc etc etc
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Four different cases
- polar solute with polar solvent
- polar solute with nonpolar solvent
- nonpolar solute with nonpolar solvent
- nonpolar solute with polar solute
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A polar solvent can separate ions such as NaCl because it __ them. If water is the solvent, the __ is called __, in which water molecules surround each ion, with the appropriate end of hte water dipole moment next to the ion.
- solvates
- solvation process
- hydration
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Because water molecuels are strongly __, a large amount of energy is __ when the sodium and chloride ions are hydrated. This energy is nearly sufficient to overcome the __ of the crystal. The salt dissolves, partly because of strong __ by water molecules and partly because of the increase in __ when it dissolves
- polar
- released
- lattice energy
- solvation
- entropy
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Nonpolar molecules of nonpolar solvents do not do what?
solvate ions very strongly, and they cannot overcome the large lattice energy fo the salt crystal
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Paraffin wax dissolves in gasoline because ?
they are both nonpolar and the molecules of paraffin are weakly attracted to each other causing vdW attractions to be easily overcome by those of the solvent
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Nonpolar-nonpolar
Althoguh there is little change in energy whent eh nonpolar substance dissolves in a nonpolar solvent, there is a large increase in __.
entropy
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Nonpolar molecules are weakly attracted to each other, adn little energy is required to separate them, but in the case of nonpolar-polar, the plar solvent is __.
strongly attracted to each other by their H bonding
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If a nonpolar paraffin molecule were to dissolve, the water molecules around it would have to __.
orm a cavity, causing fewer available neighbors for hydrogen bonding, resulting in a tighter, more rigid, icelike structure around the cavity
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Nonpolar solute-- polar solvent would do what to entropy
decrease
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