Intermolecular Forces Flashcards
What is an intramolecular force?
bonding forces that exist within each molecule and influence the chemical properties of the substance
What is an intermolecular force?
non-bonding force that exist between the molecules and influence the physical properties of the substance
What are the different kinds of intermolecular forces?
- dipole-dipole
- (ion-dipole forces)
- London dispersion forces
- hydrogen bonding
dipole = what
polar molecule
what is dipole-dipole force?
the electrostatic attraction between the ends when dipoles change their direction so that their oppositely charged ends are near to one another.
the electrostatic attraction between the molecules with permanent dipoles
The stronger a dipole or ΔEN in a molecule….
the stronger the dipole-dipole force between the molecules
what is an ion-dipole force?
the force of attraction between an ion and a polar molecule.
The charge of the ion will attract the opposite partial charge of the dipole.
what is the weakest intermolecular force between non polar molecules?
Londen dispersion forces (LDF)
What are London dispersion forces?
a temporary attractive force that results when the electrons in two adjacent atoms occpy positions that make the atoms form temporary dipoles.
both polar and non polar molecules experience London dispersion forces
Explain the temporary dipole in London dispersion forces.
- electrons are constantly moving
- at any given time there may be an unequal distribution of electrons forming a temporary dipole
- the temporary dipole will cause the electrons in another molecule to be repelled. This will cause an induced dipole
- (one atom becomes more e- positive and the other becomes more e- negative)
- there is now on average a stronger attractive force between molecules than repulsive.
What are the two factors that influence the strength of london dispersion forces?
- number of electrons in the molecule
- the effective surface area of the molecule
How does the number of electrons in a molecule impact the London Dispersion forces?
the greater the number of electrons, the stronger the London Dispersion force.
How does the effective surface area of the molecule impact the Londond DIspersion Forces?
the greater the surface area for contact between molecules, the stronger the London dispersion
atoms have to be roughly the same size for this to work.
What is a Hydrogen Bond?
a very strong dipole-dipole force
What is hydrogen bonding the result of?
Hydrogen bonding results between the interaction of the lone pair of one atom with the hydrogen atom of another molecule.
Basically, the large ΔEN that exists between a hydrogen atom and another creates a strong dipole
Where MUST the lone pair in a hydrogen bond come from? What should the other molecule involved have?
N (nitrogen), O (oxygen), or F (fluorine)
the other molecule involved should have at least one lone pair
more lone pairs in a hydrogen bond == ….
stronger hydrogen bonds
Chloring is too big to form hydrogen bonds
what is the strongest of the intermolecular forces?
hydrogen bonding
How does hydrogen bonding affected the properties of water?
- it is responsible for water’s high melting and boiling point for its size
- adhesive and cohesive properties (hydrogen bonding allows water molecules to stick to each other and surfaces, aids in transportation of water from roots to leaves in plants)
- high specific heat capacity ( heat is absorbed when hydrogen bonds break and is released when hydrogen bonds form, helping minimize temperature fluctuations in oceans etc.
- high heat of vaporization (sweating)
- water is the solvent of life
- slid form of water is less dense than its liquid form, which allows marine life to survive in frozen lakes
Melting point is a measure…
of the difference in strength of the forces between particles between the solid and liquid state.
melting point and atomic size
the larger the atomic size, the more energy it requires to melt the molecule
the larger the size, the more electrons there are moving randomly around, so the larger the London Dispersion Forces occuring between each molecule
- the sheer amount of LDF outweighs the “stronger” dipole-dipole force
