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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
Dipole moments are expressed in units of the __.
A simple rule of thumb, using common units, is that __
u (debyes)= 4.8 x δ (electron charge) x d (in angstroms)
Bond dipole moments in organic compounds range from __ in symmetrical bonds to about __ for the strongly polar triple bond.
A __ is the dipole moment of the molecule taken as a whole.
molecular dipole moment
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.
- bond dipole moments
- vector sum of hte individual bond dipole moments
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
- partial positive charge
- negative charge
- lone pair
When two molecules approach, what do they do?
attract or repel each other
In general, the forces are __ until the molecules come so close that they __ on each other's __.
- van der Waals radius
When infringement happens, the small attractive force quickly becomes a large __, and the molecules __.
- repulsive force
- bounce off each other
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
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
When two negative ends or two positive ends approach each other, they ___, but they may __ .
- turn and orient themselves in the more stable positive to negative arrangement
__ are generally attractive intermolecular forces resulting from the attraction of hte positive and negative ends of hte dipole moments of polar molecules.
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
- heats of vaporization
- boiling points
In nonpolar molecules, sucha s carbon tetrachloride, the principal attractive force is the __, one of the __.
- London dispersion force
- van der Waals forces
The London force arises from __
temporary dipole moments that are induced in a molecule by other nearby molecules
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
- dipole-dipole interaction
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
What does the attractive force depend on?
close surface contact of two molecuels, so it is roughly proportional to the molecular surface area
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
Organic compounds do not contain __ bonds, so we consider __ and __ hydrogens to be hydrogen bonded.
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
- partial positive charge
- nonbonding electrons
- nonbonding electrons on
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...
In addition to affecting boiling and melting points, intermolecular forces determine the __ properties of organic compounds.
The general rule is ?
- like dissolves like
- polar dissolves polarnonpolar dissolves nonpolar
- etc etc etc
Four different cases
- polar solute with polar solvent
- polar solute with nonpolar solvent
- nonpolar solute with nonpolar solvent
- nonpolar solute with polar solute
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.
- solvation process
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
- lattice energy
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
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
Althoguh there is little change in energy whent eh nonpolar substance dissolves in a nonpolar solvent, there is a large increase in __.
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
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
Nonpolar solute-- polar solvent would do what to entropy