Flashcards in Chapter 11 Deck (43):
intermolecular forces are generally much ____ than bonding forces
Why are intermolecular forces much weaker than bonding forces?
because bonding forces are a result of large charges (protons and electrons) interacting at close distances where as intermolecular forces are a result of smaller charges interacting at greater distances (coulumbs law)
What happens when an ion approaches a non-polar atom or molecule?
the negative electron cloud of the nonpolar atom or molecule distorts and the ion induces a small dipole in it
define ion-induced dipole forces
a intermolecular force between ions and a nonpolar molecule
what is the magnitude of ion-induced dipole forces depend on?
the charge of the ion and how easily the electrons in the atom or molecule can move or polarize in response to the presence of the ion
what is the magnitude of the polarizibility of an atom or molecule dependent on (in part)?
the size (or volume) of the electron cloud
a larger electron cloud results in a ______ dispersion force because....
the electrons are held less tightly by the nucleus and are therefore easier to polarize
define dispersion force (sometimes called the London force)
an intermolecular force exhibited by all atoms and molecules that results from fluctuations in the electron distribution in the absence of an ion
what are dispersion forces a result of?
the fluctuations in the electron distribution within atoms or molecules in the absence of an ion
what is a temporary or instantaneous dipole?
a temporary dipole caused by electrons being unevenly separated
how does an instantaneous dipole affect the atoms around it?
it can induce an instantaneous dipole in the other atoms because of the attraction of the electrons to the positive side of the atom. they then all organize themselves positive to negative
what is the magnitude of an instantaneous dipole's dispersion determined by?
how easily the electrons in the atom or molecule can mover or polarize in response to an instantaneous dipole, which partly depends on the size of the electron cloud.
for noble gases, as the number of electrons increases, the volume of the electron cloud _____, and the _____ dispersion forces result in an ______ boiling points
does the number of electrons determine the magnitude of the dispersion force? why?
not alone. shape also affects the dispersion forces (and an atoms boiling point)
atoms with larger areas for interaction will have a ______ dispersion force than atoms with smaller areas for interaction
define dipole-dipole force
an intermolecular force exhibited by polar molecules that result from the uneven charge distribution
what type of molecules have permanent dipoles?
define permanent dipole
a permanent separation of charge; a molecule with a permanent dipole always has a slightly negative charge at one end and slightly positive charge at the other
the attraction of the postive end of one permanent dipole to the negative end of another permanent dipole is an example of which force?
due to dipole-dipole forces polar molecules have a ______ melting point than non polar molecules with a similar number of electrons or of similar size
do all molecules have dispersion forces?
the ability to mix without separating into two phases
in general polar liquids _____ miscible with other polar liquids and _____ miscible with non polar liquids
define hydrogen bonding
a strong type of intermolecular bonding that occurs between polar molecules that contain hydrogen atoms bonded directly to small electronegative atoms (like O, F, or N)
as a result of the large partial postive and negative charge on a fairly small atom there is a ____ attraction between the H atom in one molecule and the O, F, or N in its neighbour. This is called....
a hydrogen bond
hydrogen bonds are not to be confused with chemical bonds. hydrogen bonds occur due to...
intermolecular forces between molecules
hydrogen bonds are _____ than a typical covalent bond
weak hydrogen bonds are _____ than the weakest dispersion and dipole-dipole forces, but the strongest dispersion forces can be as strong as what are considered to be the strongest hydrogen bonds
define dipole-induced dipole force
an intermolecular force between molecules that have a permanent dipole and an atom or molecule that is non polar
when a non polar atom or molecule and a molecule with a permanent dipole approach one another what happens?
the negative or positive end of the polar molecule distorts or polarizes the electron cloud of the non polar atom or molecule. Then because the non polar atom or molecule has a small induced dipole it can interact with the polar molecule.
what does the magnitude of the dipole-induced dipole force depend on?
the size of the dipole of the polar molecule and the polarizability of the non polar atom or molecule
define ion-dipole force
an intermolecular force between an ion and the oppositely charged end of a polar molecule
when do ion-dipole forces occur?
when an ionic compound is mixed with a polar compoud; it is especially important in aqueous solutions of ionic compounds
When thermal energy is high relative to intermolecular forces, matter tends to be ______.
When thermal energy is low relative to intermolecular forces, matter tends to be _____ or _____
Liquid or solid
Molecules with partial or temporary charges are attracted to each other because their ____ ____ decreases they get closer together
For hydrogen bonding what are the most important small electronegative atoms?
Fluorine, oxygen, nitrogen
Why have a higher boiling point than accounted for by the trend for hydrides?
Because Water has two lone pairs to accept hyrdorgen bonds and two O-H bonds to act as donors. Therefore water can participate in 4 hydrogen bonds simultaneously
Ion-dipole forces can be very ___ and are especially important in aqueous solutions of _____ ____
why does a larger electron cloud cause the dispersion force to be greater?
because the electrons are held less tightly around the nucleus and therefore are distorted or polarized more easily
if all other variables are constant, the dispersion force increases with _____ number of electrons which typically ____ the size of the electron cloud