Physical Properties Flashcards
Intermolecular forces
Forces between molecules
Dispersion Forces
- between all molecules
- weak
- temporary due to movement of electrons
- Increases with an increase in molecular mass
Dipole-dipole
- polar molecules have dipole-dipole forces
- attraction between the partial positive change at one molecule to the partial negative charge on another molecule
- stronger than dispersion
Hydrogen Bonding
- attraction between the partial positive charge of a hydrogen on one molecule to the lone pair of electrons of an O, N or F on another molecule
- strongest intermolecular force
Boiling Point
Temperature liquid changes phase into gas. Volatility is a qualitative measure of how easily a substance turns into gas
- high volatility indicates a low boiling point
Surface area
Increase surface area increase the melting point and point
- increases in branching leads to less surface area and an increase in distance between molecules which decreases the dispersion forces weaker intermolecular forces means less energy needed to overcome these forces and therefore lower melting point and boiling point
Intermolecular force present
Stronger intermolecular forces increases the melting point and boiling point. Stronger intermolecular forces means more energy needed to overcome these forces and therefore higher melting point and boiling point polarity ranking
amide > carboxylic acid > alcohol > ketane, aldehyde, amine > ester > alkanes
Melting point
Temperature solid changes phase into liquid
Boiling and melting point require sufficient energy to seperate molecules by overcoming the intermolecular forces holding them together.
The stronger the intermolecular forces, the higher the melting point or boiling point.
Molecular mass
Increase the number of carbons increases the melting point and boiling point.
Within a homologous series, adding carbons to the chain increases the mass and therefore the dispersion forces.
Stronger intermolecular forces means more energy needed to overcome these forces and therefore higher melting or boiling point.
What intermolecular force?
Organic molecule: alkane, alkene, or alkyne
Polar? Non-polar molecule
Number of polar regions: 0
Dispersion only (C-H)
What intermolecular force?
Organic molecule: aldehyde, ketone, ester
Polar? polar molecule
Number of polar regions: 1
C=O therefore dipole-dipole forces
C-H therefore dispersion forces
What intermolecular force?
Organic molecule: amine 1˚ and 2˚
Polar? polar molecule
Number of polar regions: 1
N-H therefore can H bond (donor and acceptor)
C-H therefore dispersion
What intermolecular force?
Organic molecule: alcohol
Polar? polar molecule
Number of polar regions: 1
O-H therefore can H Bond (donor and acceptor)
C-H therefore dispersion
What intermolecular force?
Organic molecule: carboxylic acid
Polar? polar molecule
Number of polar regions: 2
O-H therefore can H Bond (donor and acceptor)
C=O therefore can H bond (acceptor only)
C-H therefore dispersion
What intermolecular force?
Organic molecule: amide 1˚ and 2˚
Polar? polar molecule
Number of polar regions: 3*
N-H therefore can H bond (donor and acceptor)
C=O therefore can H bond (acceptor only)
N & O therefore strong dipole-dipole forces
C-H therefore dispersion
