Intermolecular Forces and Properties Flashcards
Types of Intermolecular Forces
London Dispersion Factors/Induced Dipole-Induced Dipole, Dipole-Dipole Attractions, Hydrogen Bonding, Ion-Dipole Attractions
Types of Intramolecular Forces
ionic, metallic, and covalent bonds
Which forces are strong? Intermolecular or Intramolecular
Intramolecular
London Dispersion Forces
Motion of Electrons create momentary dipoles
Occurs between all molecules and sometimes stronger than dipole-dipole forces
Polarizability
the ease with which the electron distribution in a molecule can be distorted (‘squashiness’ of the electron cloud)
+ Polarizability =
+ Dispersion Forces
What molecules have more polarizability?
Molecules with a greater molar mass have a greater # of electrons and, therefore, greater polarizability and more dispersion forces
Molecular shape also influences dispersion forces → if molecules can pack more tightly together in a long/cylindrical shape then they have greater dispersion forces than a spherical molecule
Dipole-Dipole Interactions
Attraction between the partially charged ends of polar molecules
+ polarity = stronger forces
Dipole-Induced Dipole Forces
A polar molecule induces or creates a momentary dipole in a neighboring nonpolar molecule
Hydrogen Bonds
Attraction between a hydrogen atom that is covalently bonded to a highly EN atom (N, O, F) and a nearby highly EN atom (N, O, F) in another molecule
Stronger than dipole-dipole but weaker than ion-dipole
Ion-Dipole Interactions
Attraction between an ion and a polar molecule
Increase in charge or polarity = increase in force
Smaller ions have stronger attractions with polar molecule
Comparing Relative Strengths of IMFs in two substances
If they have similar molar masses and shapes then dispersion forces are ~equal in the substances-more polar molecules have greater attraction
If they have very different molar masses, then dispersion forces are the most important attractive forces-the bigger the molecule, the greater the number of electrons, the greater the polarizability, the greater the dispersion forces
Ranking Strengths of Intermolecular Forces
Dispersion Forces, Dipole-Dipole, Hydrogen Bond, Ion Dipole Interactions
Vapor Pressure
The pressure exerted by a liquid’s vapor phase when the liquid and vapor states are in equilibrium
Increase in temp = Increase in vapor pressure
Volatile
Liquids that evaporate easily due to low IMFs
Increase in IMFs = increase…
Melting point, boiling point, surface tension, viscosity (resistance to flow), heat of vaporization (energy required to evaporate)
Increase in IMFs = decrease…
Vapor Pressure, volatility
Types of Solids
Metallic Solids, Ionic Solids, Covalent-network solids, Molecular Solids
Ionic Solids
Held together by electrostatic attraction between cations and anions held in a 3D lattice structure
High Melting and Boiling points
Brittle
Poor conductors of electricity unless they’re aqeuous
Molecular Solids
Held together by IMFs
Relatively low melting and boiling point due to the weak IMFs holding the molecules together
Poor conductors of electricity because the electrons are held tightly in covalent bonds
Covalent-Network Solids
Formed by atoms all held together in large networks by covalent bonds
Hard solids, high melting points due to being held in solid state by covalent bonds
Types of Covalent-Network Solids (8)
diamond, graphite, silicon, germanium, quartz (SiO2), silicon carbide (SiC), boron nitride (BN), and boron carbide (BC)
Metallic Solids
Held together by delocalized ‘sea’ of collectively shared valence electrons
Great conductors of heat and electricity
Melting points vary depending on the element
Polymers
Contain long chains of atoms (usually carbon), where atoms within a chain are held together by covalent bonds but adjacent chains are held together by IMFs
State of matter depends on…
balance between the kinetic energies of the particles
the attractive forces between the particles
Ideal Gas Law
PV=nRT
STP
0 degrees Celsius, 1 atm, and 1 mole of gas occupies 22.4L
1atm =
760 mmHg=760 torr=101.3 kPa
Molar mass equation
M = dRT/p