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CHEMISTRY U4 AOS1 > Properties > Flashcards

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


define: viscosity

measure of a liquid’s resistsance to flow.
stronger the intermolecular forces (bonding/size/sahpe) the more viscous.


describe: flashpoint

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)


how do we differentiate bt bp's

whether things can form hydrogen, dipole-dipole or disp forces - determines strength
alkeanes, alkenes, alkynes
aldehydes, ketones, esters
alcohols, carb acids, amines, amides