Flashcards in Properties Deck (14):
define: polar bonds
when one atom is more electronegative than other other so electrons are pulled towards it, forming dipole positive and negative.
how are non polar bonds formed
only when the bond is between the same elements
how can polar bonds form a non polar molecule?
if the molecule is symmetrical/polarity cancels out.
define: dispersion forces
present in all covalent molecules due to their ability to form an instantaneous dipole (due to random movement of electrons)
as molecules get bigger
more dispersion forces can form...
define: dipole dipole bonds
attraction between positive negative dipoles.
greater the difference in dipoles the stronger the bonds.
define: h bond
attraction between hydrogen and the most electronegative elements (FON)
ion dipole bonds
between charge on an ion and the dipole of a polar bond.
describe boiling point
changing from a liquid to a gas involves breaking intermolecular bonds. The stronger these bonds, the more difficult to break and the higher BP.
strength of intermolecular bonds?
effect of shape on bp?
having branches means molecules cant pack as thighly together. results in weaker (??) disp forces and lower bp
measure of a liquid’s resistsance to flow.
stronger the intermolecular forces (bonding/size/sahpe) the more viscous.
the lowest temp at which the vapour of a liquid fuel will ignite when an ignition source (eg. flame) is applied.
As the temp of a liquid fuel increases, the conc of its vapour increases. At a certain concentration (hence temp) there’ll be enough vapour mixed with air for the fuel to ignite.
In order to become a vapour the fuel needs to boil – therefore flashpoint is indicative of boiling point (bonding/size/shape)