covalent bonding 2

what is electronegativity

a measure of the tendency of an atom to attract a bonding pair of electrons

in what example are electrons shared equally between two atoms

diatomic molecules have equal tendencies to attract the covalently bonded electron pair and there is no difference in electronegativity

what is electronegativity

a measure of the tendency of an atom to attract a bonding pair of electrons

in what example are electrons shared equally between two atoms

diatomic molecules have equal tendencies to attract the covalently bonded electron pair and there is no difference in electronegativity

how to remember the diatomic molecules

BrINClHOF

are covalent bonds polar or non-polar

they can be both

why can covalent bonds be both polar or nonpolar

if there is any difference of electronegativity the bond is polar, since covalent compounds can have differences of electronegativity they can be polar

covalent compounds which are non polar can come from either diatomic molecules or cancelling out of dipoles

what is a polar bond

when electrons are distributed unequally within a bond so one side with be delta positive and the other will be delta negative

what does the polarity of the bond depend on

the difference of electronegativity between the two atoms

the higher the difference of electronegativity....

the more polar the bond

what the actual frick is a dipole then

a dipole is a measure of how polar a bond is (how high the difference of electronegativity between the atoms in a bond)

how is a dipole represented and which way does the arrow go

the arrow points to the delta negative side of the bond/ the more electronegative side

how to determine whether a molecule is polar

have to look where the dipoles are in a molecule

(unless diatomic they will always have dipoles)

and see if the shape cancels the dipoles out

what direction should two dipoles be in relation to one another to be classed as 'cancelled out'

away from each other

is this polar or non polar ->

POLAR BECAUSE THEY DONT CANCEL OUT BECAUSE THEYRE GOING TOWARDS EACH OTHER

is this polar or non polar ->

NON POLAR BECAUSE THEY CANCEL OUT BECAUSE THEYRE GOING AWAY FROM EACH OTHER

is co2 polar or non polar

draw lewis diagram

nonpolar as its dipoles cancel out as theyre going away from each other

is NH3 polar or nonpolar

polar, dipoles do not cancel out and even if they did the lone pair affects the shape of the molecule

NH4 polar or nonpolar

nonpolar but not because the bonds cancel out because they dont but instead because its symetrical

CCl4 polar or nonpolar

non polar becuse the dipoles cancel out

what are the ATOMS within a single simple molecule held together by

covalent bonds

how are the different MOLECULES in simple molecular structures held togther

if you said covalent bonds close the laptop and jump off a cliff because youre actually cooked

its intermolecular forces between the MOLECULES and covalent bonds between the atoms within the molecules

what is really really really REALLY important to know about intermolecular forces

they occur between the simple covalent molecules to hold those together unlike the giant covalent which are made held together

what are the 3 types of intermolecular forces

london dispersion forces (instantaneous dipole induced dipole)

dipole induced dipole

dipole-dipole interaction

hydrogen bonding

what are the weakest of the intermolecular forces

london dispersion forces

what contains london dispersion forces

literally every single molecule ever created ever on this earth ever has london dispersion forces

what are london dispersion forces

they are temporary/instantaneous dipole induced dipoles where one atom becomes temporarily a dipole causing adjacent atoms to be attracted/repelled

how does a london disperion force come about -how can everything including nonpolar bonds have a temporary dipole

well because electron motion is constant within atoms, so if too many electrons move to one side even for a second it makes a dipole which makes delta positive side and delta negative side so adjacent atoms are either attracted or repelled which makes a dipole in that atom causing attraction/interaction

although london dispersion forces are just weak (like will) they can still vary in strength what are the two things that affect london dispersion forces strength

surface area

number of electrons

how does the number of electrons affect london dispersion forces

the more electrons the greater the likelihood of temporary dipole the MORE FREQUENT, and the greater the magnitude of the temporary dipole

what can we compare to show the strength of intermolecular forces

energy needed to boil and vaporisation

the stronger the intermolecular force

the higher the energy needed to boil and vaporise it

how to compare the effect of no of electrons on london dispersion forces

go down the noble gas group (has to be noble gases because they all only have london dispersion) and measure bp

what do you HAVE to be careful of

which type of intermolecular force is in which

they ALL have london dispersion forces but some have other forces too like hydrogen bonds or dipole-dipole etc so it will affect it

explain why the bp increases down group 8

more electrons so more frequent temporary dipoles with ahigher magnitude so stronger london dispersion forces

how can surface area affect the strength of london dispersion forces

more surface area of a molecule the more interaction itll have with adjacent molecules the greater the ability to induce another dipole when it becomes an instanteaous dipole so the greater the london forces

how can you compare surface area affect on london dispersion forces

using ISOMERS because theyre molecules with the same atoms but arranged differently

explain dipole induced dipole interactions

permanent dipoles can cause temporary dipoles in nonpolar substances

acts in addition to london dispersion

example of when you would see dipole induced dipole

mixture of polar and nonpolar molecules e.g HCl H-Cl (polar) is a dipole causing Cl-Cl (nonpolar) to become a temporary dipole

explain DIPOLE-DIPOLE interactions

when a permanent dipole is attracted or repelled by the delta positive or delta negative side of another permanent dipole

acts alongside london dispersion forces

what can you compare to prove dipole-dipole interactions are stronger than london dispersion forces and why

propanone and butane because

-they have the same number of electrons so wont affect the london dispersion forces

-butane is non polar so it will only have london dispersion forces

-propanone is polar so will have dipole-dipole interaction

compare propane and butane

due to the dipole-dipole interaction in propanone because of its polar character it has a higher boiling point as more energy is needed to break the bonds between the interactions then in butane because butane is nonpolar and only consists of london dispersion forces which do not require as much energy to break

order of strength of intermolecular forces

london dispersion, dipole induced dipole, dipole-dipole, hydrogen bonds

what does hydrogen atom have to BOND with for hydrogen bonding MY FAVE ACRONYM EVER (back to atoms apparently)

ONF

Oxygen

Nitrogen

FLourine

why those three

because it gives the greatest difference in electronegativity because they are the most electronegative substances -strongest bond for a reason am i right

strongest type of intermolecular force

hydrogen bonding

what are the 4 main giant covalent structures you need to know

graphite/graphene

diamond

buckminster fullerene aka c60 fullurene

silicon/silicon dioxide

what are all giant covalent molecules in relation to carbon

they are all allotropes of carbon except silicon dioxide

meaning they are made of entirely carbon

structure of diamond

1. tetrahedral structures

2. bond angle 109.5

bonding in diamond

1. each carbon covalently bonded to 4 others forming tetrahedral

2. bond angle of 109.5

structure in diamond

each carbon covalently bonded to 4 others forming tetrahedral

(diamond is pretty boring, comparing it would mainly be 'and diamond doesnt' ifykwim)

uses of diamond

jewellery and cutting tools

bonding in graphite

-each carbon is COVALENTLY bonded to 3 other carbons to form a layer of hexagonal rings

-bond angle 120

-delocalised electron free to move and carry a charge

structure of graphite

-each carbon covalently bonded to 3 other carbons forms layer of hexagonal rings

-bond angle 120

-intermolecular forces holding the layers together

-delocalised electrons free to move and carry a charge

bonding of buckminster fullerene

made up of 60 fullernes

each carbon COVALENTLY bonded to 3 others

delocalised electrons

bond angle 120

structure of buckminster fullerene

football shaped

made up of pentagonal and hexagonal rings

semi-conductor due to delocalised electrons free to move and carry a charge

bonding of silicons in just silicon and the structure

each silicon is covalently bonded to 4 other silicons

tetrahedral silicon structure with bond angle of 109.5

similarities between all covalent lattice structures

they all have high mp/bp, require lots of energy to break the bonds

insoluble in water

physical differences

graphite can be soft (layers slide yk)

diamond and silicon very hard

what are van der vaals forces specific to

everything but hydrogen bonding

london dispersion

dipole-dipole

dipole induced dipole

when asked to draw two different hydrogen bonding interactions

look for a link between hydrogen and ONF

but then also there will most likely be a hydrogen on the other which can link ONF in the same way

e,g CH3OH and H20

the h on ch3oh can link to the o on h20

but also the h on h20 can link to the o on ch3oh you feel me

2 requirements for hydrogen bonding

1. hydrogen must be bonded to O N or F to be electronegative enough to form a bond to another molecule

2. there must be lone pairs on the O N or F

this must happen on both molecules if they are different

can two methanals CH2O form hydrogen bonds together

no

lone pairs on oxygens yep

but the hydrogen is not bonded to the O have to draw out lewis structures to figure out

can methanoic acid CH3OH form hydrogen bonds with water H2O

yes because methanoic acid has a hydrogen bonded to ONF and ONF has lone electrons

water also has a hydogen bonded to ONF and ONF has lone electrons

both ONF is oxygen in this case