Physical Properties Flashcards
Intermolecular forces
Forces between molecules
Dispersion forces
Between all molecules
Temporary due to movement of electrons
Weak
Increases with an increase of molecular mass
Dipole-dipole forces
Polar molecules have dipole-dipole forces
Attraction between partial positive side of one molecule to the partial negative side of another molecule
Stronger than dispersion
Hydrogen bonding
Attraction between the partial positive of a hydrogen on one molecule to the lone pair of electrons of an O, N or F of another molecule
Strongest intermolecular force
Boiling Point
Temperature liquid phase changes into gas
Volatility is a measure of how easily a substance turns into gas with a high volatility indicating a low boiling point
Surface area affects melting and boiling point
Increasing surface area increases the melting and boiling points
Increases in branching leads to less surface area and an increase in distance between molecules which decreases the dispersion forces
Weaker IMF means less energy needed to overcome these forces and therefore decreased melting and boiling point.
Intermolecular forces affect melting and boiling point
Stronger intermolecular forces increase the melting and boiling point
Polarity ranking of molecules (most to least polar)
Amide, carboxylic acid, alcohol, (ketone, aldehyde, amine), ester, alkane
Melting point
Temperature solid changes phase into liquid
Molecular mass affects melting and boiling point
Increasing the number of carbon molecules increases the melting and boiling point
Within a homologous series, adding carbons to the chain increases the mass and therefore the dispersion forces
Answering physical properties questions
Structure of molecules, IMF present, strength of IMF, answer
Solubility
Physical property referring to the ability for a given substance (solute) to dissolve in a solvent
Solute will dissolve in solvent if the solute-solvent IMF are equal to or greater than solute-solute and solvent-solvent IMF
Like dissolves like (Polar solutes dissolve in polar solvents e.g. water and same for non polar)
Polarity affects solubility
Polarity of each molecule due to its functional groups will change its solubility
More polar groups in a solute make it more soluble in a polar solvent, but less in a non polar solvent
Carbon chain length affects solubility
As carbon chain length increases, the non-polar portion of the molecule increases and the solubility of the solute in non polar solvents decreases
Generally a polar molecule with four carbons or less are soluble in polar solvents, after four, solubility in polar solvents is limited
Molecules that are soluble in polar and non polar solvents
Polar (water): amides, carboxylic acids, alcohols, ketones, aldehydes, esters
Non polar (hexane and benzene): hydrocarbons, haloalkanes
