Intermolecular Forces

which state of matter has the strongest interparticle attractions?

solid

which state of matter has the weakest interparticle attractions?

gas

what are intermolecular forces?

attractive forces between molecules

what are intramolecular forces?

attractive forces that hold atoms together in a molecule

are intramolecular or intermolecular forces weaker?

intermolecular forces are weaker

what are London Dispersion Forces?

weakest force, found in nonpolar molecules and every kind of compound

what is an induced dipole?

occurs between nonpolar compounds because electrons are always moving; the nonpolar compounds become temporarily polar when they come in contact

what is polarizability?

the ease of electron displacement

how is IMF proportional to boiling/melting point, heat of vaporization, heat of fusion, and vapor pressure?

IMF is directly proportional to all except vapor pressure, which it is disproportional to

how do you know which molecule has a higher boiling/melting point than another if both only contain LDF?

look at their total electrons

do ions form molecules?

no

what makes up a molecule?

two nonmetals

what happens if nonpolar molecules don’t contain LDF?

they can’t condense to form liquids or solids

what is the relationship between the number of total electrons in a molecule and polarizability?

they are directly proportional

what is a dipole moment?

when the more electronegative atom in a molecule pulls the electron density of the bond closer to itself, giving it a partial negative charge and leaving the other atom with a partial positive charge

what are dipole dipole interactions?

found between polar molecules

what are ion-ion interactions?

interparticle forces between ions, generally the strongest

what is hydrogen bonding?

a type of dipole-dipole interaction found between H and F, O, N

what are network solids?

solids made of multidirectional covalent bonds with a unique type of and the strongest IMF; diamonds, graphite, silicon dioxide

what are the effects of hydrogen bonding?

increases melting/boiling point, increases heat of vaporization, decreases vapor pressure; causes ice to be less dense than water

what is the most common physical state for only LDF?

liquid and gas, never solid

what is the most common physical state for dipole-dipole interactions?

liquid

what is the most common physical state for hydrogen bonding?

liquid and some gas

what is boiling point?

the temperature at which the vapor pressure equals the external pressure

what is the normal boiling point?

the temperature at which the vapor pressure of a liquid is equal to 1atm

what is surface tension?

the amount of energy required to stretch or increase the surface of a liquid by a unit area

which has the higher melting point, NaCl or NaF? explain

although both molecules have ion-ion interactions, NaF has a higher melting point because its atomic radius is smaller and the atoms are closer together which means it requires more energy to separate them

what is Coulomb’s Law?

the electrostatic force between two charged particles is directly proportional to the product of their charges and inversely proportional to the square of the distance between them

why do halogens go from gases to a liquid to solids as you go down the group?

the number of electrons increases, which increases size, distance between the particles, polarizability, and the strength of the IMF

what is the state of aggregation?

the physical states of solid, liquid, or gas at a certain temperature

distinguish primary bonding from secondary bonding

primary bonding is generally intramolecular forces while secondary bonding is intermolecular forces; in the case of noble gases like Ar, the primary bonding is LDF

what is the physical state of most substances that have ionic bonding?

crystalline solids

what does covalent bonding lead to?

discrete molecules and network solids

what is the most common disruptive force used to break cohesive forces between molecules?

thermal energy

how can we determine the physical state of a substance?

by bringing 2 molecules or atoms close together

what are the two influences that affect time fluctuating dipoles?

size of electrons and number of electrons

what is activation energy?

the amount of energy required to remove the outermost electrons from a gaseous atom in the ground state