Comprehensive AQA Atomic Structure Revision Guide Explained

[Music] hello my name is Chris Harris and I'm from allery tor.com and um this video is

basically we're just going to go through uh AQA atomic structure um so this is specifically for AQA um and uh basically

was going to go through um the key points just as revision it's a good overview of the topic to make sure that

that um you've covered most of the things that you need to know um and just before I start um the Powerpoints that

I'm using here that I've made uh they are available to uh to purchase if you just click on the link in the comments

box uh just below then you should be able to uh click on that and you'll be able to buy them there if you're

interested it' be great for things that you can print them off or you can look at them in your own time um you know use

them as revision notes um whatever so they they're quite quite colorful so they should be uh reasonably attrative

to use okay right so let's make a start like I say all of these things they are um Ted to the specification um so to

make sure that they are absolutely watertight um well nearly um so uh you can look at the specification basically

just matches that okay so we're going to start with the atom so the atom as you can see is mainly made up of protons and

neutrons they are very small and they contain um that are contained in the middle there you also have electrons

that's whizzing around in um shells so these orbit the middle of the atom as you can see um you need to know these

charges as well so protons have a positive charge as you can see there it is there and neutrons have a zero charge

Neutron neutral electrons are negatively charged so they have a minus one charge their relative masses you need to know

is one one and one over 2,000 is the relative mass of electron you can't put no Mass electron does have a mass it's

just very very small um and just to familiarize yourself with the um the elements in particular so here's lithium

for example the the top number tells us the mass number it's the number of protons and neutrons in the nucleus and

the bottom number tells us are just the number of protons we call this the atomic number or proton number so um

yeah so all atoms remember are neutral uh because the number of protons equals the number of

electrons okay right so let's look at some ions and isops so you've got to know the difference between these um

we'll start with ions first so ions have a different number of electrons and protons um so they basically don't have

equal amounts like we looked at in an atom so for example if we look at negative ion O2 minus has gained two

electrons to get a full stable shell of electrons so um you can see here that um the protons in this particular one here

that we have eight protons which give a charge of plus eight eight neutrons they have no charge so they don't um they

don't count electrons we got 10 electrons in O2 minus that means it gives it a minus two charge so the total

charge on this is minus two and that's how we work out them charges okay so um this basically allows them to form these

stable ionic compounds they gain stability by being attracted to positive ions okay so let's look at a positive

ion this is sodium uh sodium is the opposite it has one electron in its outer shell it's in group one um it uh

loses an electron um to form a na+ ion and um you can see the same calculation I've done protons 11 protons it's got 12

neutrons which have no charge um and electrons CU it's lost electron and now only has 10 electrons so the charge is -

10 now if you do + 11 0 and - 10 you get an overall charge of + one that's why sodium has got a positive charge okay

Isotopes right these are elements with the same number of protons but a different number of neutrons so um they

have a different Mass effectively so these are slightly different so let's look at these three examples here this

is three examples of carbon carbon 12 carbon 13 carbon 14 um and let's just look at the different numbers you can

see see we've got the protons neutrons and electrons here um now if we look here they've got the same number of

protons each all of these Isotopes to but crucially the number of neutrons is different so carbon 12 has six neutrons

carbon 13 is seven and carbon 14 has eight neutrons so these are isotopes of each other okay chemically they react

the same because they have the same number of electrons um but they have a slightly different

Mass okay right we need to know a little bit about the history this is the fun bit okay back in 1803 John Dalton he h

came with this idea that atoms were all spares a very simple idea uh and it wasn't until um a good while later

nearly 100 years later that JJ Thompson had a good go at trying to change the model that Dalton came up with he

discovered the electron uh and the atom he said basic the atom wasn't solid and it was made up of other particles and he

named it the plum pudding model um so basically he said that you had the positive pudding bit which is this bit

here and inside the pudding you had negative electron which are the yellow circles there that's what Thompson came

up with um very shortly after that um Ernest Rutherford caught the atom the the atomic bug I suppose and he

discovered the nucleus um and also discovered that the nucleus was really really really small uh and actually the

nucleus contained positive charges so he basically said that most of the atoms empty space um because the nucleus was

so small and he said we had a cloud of electrons that was surrounding this nucleus so you can see now we're

starting to resemble more like the atom that we know today um and he proved this using the

gold leaf experiment um basically what he did is he fired alpha particles at a very thin bit of gold leaf uh and most

of the alpha particles went through now that tells him that most of it was empty space so that kind of that's where he

got his idea from um but some did deflect back very very small number and so what they must have done is they've

hit a small positive nucleus um because an alpha particle is positively charged so um so it's actually hit the nucleus

and it's bounced back some of it was deflected some of it bounced straight back right back at the um at the the the

uh the source of the alpha okay so 1913 again look not many years later uh Neil's B had a go over it so they

already got the the atomic bug here and he discovered a problem with Rutherford's uh model and basically he

said well the electron cloud could collapse because it would obviously fold into the positive charge nucleus um and

so he said well actually you couldn't just have a cloud you had fixed energy levels and this is where the shell came

up with now basically um the uh he uh proved this cuz actually when he shown electromagnetic radiation um it was

absorbed by the atom and the electrons move between the shells that's what he noticed and when they do this they emit

radiation when the electrons move back down to a lower energy level now this could only be explained using a shell

model um you couldn't explain this using the cloud model so um this basically um kind of cemented Neil's ball idea of the

atom okay and obviously the model today we know that actually yes there are shells but we now know of the existence

of subshells um and basically we can use the ionization Trends to explain this which we'll look at later okay um the

Tim of flight Mass spectrometer so this is basically Mass spectrometry but using time of flight uh the first bit when you

add your sample it's vaporized um so it can travel through the time of flight Mass spectrometer so we turn it into a

gas basically um then we ionize it now we can ionize this using a we call it electr spray ionization this basically

works when we spray uh a sample through a high press jet it's like putting your thumb over a hose pipe it's really high

pressure jet uh and basically what they do is they pass a really high voltage through this jet uh and this causes the

loss of an electron um and um what we get is a gaseous positively charged sample is made um and this is really

important because we need ionization for the next stage which is acceleration um so you can see there there's the blue

particle look um they're moving through um so these are accelerated by negatively charge plates or an electric

field um and basically the particles with a lower Master charge Ratio or MZ ratio will accelerate quicker so they'll

move through a little bit quicker okay um and the next bit is the basically is the iron drift this is a bit weird now

you can see the red ones zipped through there and the blue ones a little bit slower um but the particles travel

through with a constant speed and kinetic energy so um if I just go if I just go back you can see look both

they're traveling at the same speed and the and the blue one they're traveling at a constant speed sorry not the same

speed traveling at a constant speed but they do have between them they have a different speed each but their speed is

is the same in terms of the the atom so in other words the red atom constantly travels through it doesn't speed up or

slow down as it goes through the iron drift it travels through at a constant speed but the blue one goes slower um

and then the final stage is detection so once it's drifted through um obviously the Blue's going a bit slower than the

red then um a basically an electrical current is made when the particle hits the plate at the back um and basically

ones with a lower MZ other words lighter particles will reach the detector first as they travel the fastest so we have a

acely separated our different parts out and we're detecting them at the other side okay right your definitions right

you need to know these I can't emphasize this enough all right relative atomic mass you can probably read them there

pretty straightforward relative atomic mass is the average mass of an atom of an element when measured on a scale on

which the mass of an atom of carbon 12 is exactly 12 basically we're measuring everything relative to carbon 12 the

relative molecular mass so this is very similar if you look the average mass of a molecule when measured on a scale uh

which the mass of an atom is carbon 12 is exactly 12 so this is a molecule instead of an atom and relative isotopic

mass is basically the mass of an atom of isotop with an element measured on a scale in which the mass of an atom of

carbon 12 is exactly 12 so there's a lot of carbon 12 being mentioned here you've just got to know these really okay let's

look at a mass Spectra okay so here we are we've got a um this one we're going to look at Isotopes um so we've got an

element here and it's made up of Toops now the first thing we need to look at really um is the um the axes so you can

see here that we've got a Master charge ratio at the bottom um this is basically the mass of the isop divided by the

charge um and most do have a plus one charge um and so this makes it the same as the isotopic mass um which makes it

relatively straightforward if it um had two electrons knocked off which would be quite rare um then the obviously the

mass the charge ratio will be half as much um so that's quite that's quite important um because obviously the Z bit

bit um stands for charge so if you've got a double charge it's just the mass of the isotope divided by two okay um

the bit in the side read this really carefully I mean this is the abundance um it's always shown on the left but

this one it can be written as a percentage or a nominal value so it can be just a relative abundance this one's

percentage abundance so this means that all your Isotopes must give 100% if it's a percentage abundance because obviously

you can't get bigger than 100% okay um so you can see here if we have the 75 and uh 25 and can get 100% from there

okay so this Spectra shows two isotopes of one element so we' got one element going through here made up two isotopes

and we know this because we've only got two peaks so we've got one isotope that has a mass of 35 and one that has a mass

of 37 um this is assuming obviously they have a one plus charge so um you can see here the the most abundant which means

the most common isotope is uh isotope 35 whatever this is uh 37 isn't as common okay right so and from all this

information we can work out the relative atomic mass which we're going to look at now which is pretty useful okay so let's

work out the relative atomic mass of these you need to know this formula um relative atomic mass is the abundance of

isotope a Times by The MZ of a so that's the Master charge ratio of a plus the abundance of B Times by The MZ of B and

if you had more than two um you would just literally keep adding up the abundance of a abundance of B and

abundance of C Etc you just keep adding them up so basically um you you keep adding loads of these brackets repeating

it for each ice tub divided by the total abundance now because this one's percentage abundance our total abundance

is going to be 100 but it might not be percentage so kind of look out for that okay so let's look at this relative I

relative atomic mass sorry is going to be 75 * 35 because the abundance of a is 75 the uh mass of a is 35 Mass to charge

sorry is 35 so we do 75 * 35 plus 25 * 37 so that's them two uh divid 100 equal 35.5 and if you're smart enough you can

look in the periodic table and you can identify that as chlorine um so you've effectively identified your element from

your mass spectrometer so that's pretty nice and straightforward um you can also do it

through tables as well um you don't have to give it through Spectra um similar thing this one's got more isops as you

can see we don't know what the element is of the relative of time Mass but we're going to try and work it out so

here's that equation again look all we're doing is taking the isotope multiplying it by the abundance 20.5

there it is 70 * by 20.5 plus and then here's your other Isotopes I was talking about so you just basically add them up

it is a percentage abundance so we divide it by 100 if it's not then we just add these numbers up and divide by

the total of them numbers okay so the answer is in this case is 72.6 this means that this

element is geranium and you can have a look in the perct table and check that out okay uh right molecules um you don't

need to know a lot about molecules at as um thankfully um so um not for the first year anyway um you need to know a little

bit more for the second year but not for the first year um just to show you look I've changed the axes on the left this

is um this is obviously relative abundance um so I've changed it slightly it's not percentage abundance anymore so

we just add up all these masses if we want to work out the the the total amount okay uh molecules are different

um we RMZ there um molecules are different because when we send them through the mass spectrometer they

actually break into little bits and we call them fragments um don't worry too much about fragments at as um but the um

the fragments uh have a mass and um basically we have an instead of isotopes that we have in an element we have these

bits and these fragments obviously form the uh the Spectra that we can see here the most significant thing that we need

to know is the m plus1 Peak basically this is this uh Peak shows the uh fragments of the um uh that hasn't been

broken up so basically if we had say if we had ethane for example uh this is unfragmented ethane the whole thing has

been ionized and the whole molecule has gone through because some molecules aren't fragmented um and basically we

get what we call a molecular ion Peak which is always the last significant Peak on the Spectra so in this case the

last one in here is 50 so we can know that this molecule has a MZ or mass of 50 um so that's pretty much all you need

to know about that okay just looking at electric configuration um we need to know that

electrons are split into four subshells we have the S the P the D and the F okay and we need to know how to we how we how

we write these um these uh electrc configurations as well so s is only one orbital it's spherical it can only hold

two electrons your P are like in a figure of eight um and they hold um two El Rons each each orbital but we have P

we have three p orbitals so in total we can fit six electrons in the p subshell uh the D orbitals are the um

again you only fit two in each orbital um but we have five of them so in total we could fit 10 electrons in the d sub

uh subshell and the F block uh is that funny block that's kind of detached away from the P table right at the bottom uh

these basically have seven orbitals and you could fit 14 electrons in total here so let's look at the um the the shell

number first so if we look at an atom the first shell only has one s orbital that's all it has uh and the maximum we

can hold is two so we've done that in green to match in Shell number two in an atom um we have the 2s orbital you can

see now we've still got an S orbital but now it's the 2s orbital and now we start to get into P orbitals electrons and P

orbitals again we can fit a maximum of eight electrons in the second shell and because we can have six in the p in the

third shell um we can have we now have a d orbital and D orbitals remember can hold 10 electrons so if we have two in

the S remember this is 3 S 3p and 3D um because we have three in the S um then um so because we have two

electrons that can fit in the S we have a two there uh we have two lots of uh three p orbitals uh or three lots of 3p

orbitals with two electrons each um so and you can see here that we've got five uh 5D orbitals here which is 5 * 2 and

that's 18 okay so this just basically shows you how it's all structured okay so let's

look at the electric configuration okay of of an atom so uh basically we need to know that they're written like this 1 S2

the first number here tells you the shell number the letter bit here tells you the subshell that we've just looked

at before and the number bit tells you the number of electrons in that subshell so let's look at the electrical

configuration of I I okay um so you can see here that we've got 26 protons this is Elemental ion so we've also got 26

electrons so basically we just need to look and see what the electric configuration is what I've done is we've

drawn an energy level diagram to show you how these orbitals correspond to each other in terms of energy so we have

1 S2 U basically we got to get 26 electrons 2 S2 so you can see here that we've got the second shell now uh s

orbital we've got two electrons in the S orbital and we represent them with a box the Box the little arrows show electrons

spinning so spinning in opposite directions okay 2 P6 3 S2 and you can see we're filling

them up remember the p orbital we can have three orbitals in there uh P subshell so we have three

orbitals uh 3 P6 and then 4s2 now it's a bit weird if you look here your 4s2 is lower in energy than your 3D this

doesn't have to be in numerical order um but yeah your 4S is lower than your 3D so we fill that one first uh and then we

have 3d6 um and so obviously this tells us the electrical configuration of iron um and you can see that configuration

there okay so check they must give or they should add to give 26 so just check check them answers that okay we always

fill from the lowest energy upwards so we start from the 1s first we can't start from 2p or anything you have to

start from the 1s and um we fill orbital singly as well first then we pay them up so if you look at that top row there

where we're pointing to you can see that we've got these electrons that are single in other words they don't put

that electron in that orbital they prefer to sit separately uh in their own orbital unless they have to pair up

because there's no other orbitals left okay so um and this is because obviously got electrons off the same charge and

we've got a bit of repulsion going on okay let's just look at some ions so with ions you just have to remove the

electrons from the highest energy level first so transition metals behave a little bit differently we'll have a look

at them later so let's look at the electric configuration for calcium 2+ what this does is this loses two

electrons um and you lose the two from the 4S so let's just have a look there's the

4s2 and there it goes it disappears and what we're left with is your

3p6 um because we've taken the electrons from the 4s2 uh and basically we need to check check the small numbers so they

should give um these numbers here if you add them up it should give 20 minus 2 cuz we're taking two electrons away is

18 we add all them up it should give 18 okay so we lose from the 4S okay there it goes and it

disappears okay transition metals are a little bit different um you've got to be careful with these chromium and copper

in particular okay so they behave differently so an electron from the 4S orbital actually moves into the 3D

orbital to create a more stable half full or full three dub uh 3D subshell respectively okay so if we look at

chromium okay so the uh electron configuration of chromium um is 1 S2 2 S2 2p6 3 S2 3p6 3d5 4s1 so what we've

done is we've removed an electron from the um uh

the uh 4S orbital um or the 3D orbital should I say so we removed an electron from there however an electron from the

4S orbital has moved into the 3D subshell so we've created a half full subshell so what we don't do is we don't

take from the um basically we don't have this situation here where we take from the D orbital and we still have two in

the S orbital so this is a bit unusual really so um so these things behave a little bit differently as well uh so

your metal ions these behavor a bit strange so if we look at the electrical configuration for f

fe3+ um so basically what it does it loses three electrons and two from the 4S and one from the

3D okay which is a bit strange so normally you would think you would remove from this one first and because

of sign energy but when you're removing from a transition metal because these things are so close in energy we

actually remove these ones first um it's more stable less energy to do that then we start picking away from the 3D so

let's just have a look um there it is there this is the electron configuration for uh ion and what we're going to do is

we're going to remove there you go the electrons from there and we got 3d5 let's just go back look there so we take

three electrons 4s2 goes 3d6 turns into 3d5 let's look at it uh in terms of the numbers if you add them up it should

give 26 - 3 which is 23 so just check the Little Numbers there look on this diagram there it is loose in the

4S there you go then from the 3D and there's the configuration okay so you got to loen the 4S first

right let's look at ionization so this is the minimum amount of energy required to remove one Mo of electrons from one

mole of atoms in the gaseous State you must all these bits which are underlined you've got to remember it's always one

mole one mole of atoms one mole of electrons Etc always got to be in the gaseous State as well I know it looks a

bit weird when you've got when you ionizing sodium and sodium is in the gas state or gaseous state but it's always

got to be like that okay so let's look at sodium sodium is na uh forms na+ + one electron

this is the first ionization energy of sodium and it's given the value there you don't obviously have to remember

these values okay always include your state symbols like I say and ionization energy always ionization so it always

requires energy um so um these things are always endothermic um so they always have a

positive value okay that's always with all ionizations okay um we need to know about the effect of shielding this is

quite important U basically the more shells or electron shells that we have between the positive nucleus and the

outer electron the less energy is required and we've got a weaker attraction here so there's your positive

nucleus look at this at's got loads of shells here there's the outer electron so trying to take an electron from there

is going to be a little bit easier than taking an electron from there because you got a stronger attraction between

the positive and the outer electron compared with this one this one has more shielding okay atomic size that's going

to play a role as well so the bigger the atom the further away the electrons are from the nucleus the attractive force is

weaker so therefore it takes less energy to remove that outer electron and the nuclear charge is pretty important as

well so the more protons in the nucleus the bigger the attraction is between the nucleus and the outer electron um so

this means more energy is required to remove the electron this is particularly useful if you're looking at Trends going

across a period which we'll look at um later on okay right right so let's look at

successive ionization energy so this is basically removing an electron from an atom so we're constantly taken take the

first electron then we take the second then we take the third then we take the fourth Etc so that's what we're going to

do here so the removal of one of of sorry the removal of more than one electron from the same atom is called a

successive ionization so here's magnesium we're going to remove an electron from something that's already

positively charged this is called the second ionization energy look it's a little bit bigger compared to the one um

which would be for the first ionization so um this is the second one here so it takes a little bit more energy we're

trying to remove something from something that's already positively charged that's going to take some energy

to do okay so you can see we've got some distinctive jumps here um so we've got jump here and we've got a jump here now

these jumps are because we're removing an electron from a shell that's increasingly closer to the nucleus um

because it's closer to the nucleus remember this the nucleus holds these electrons in so um this is going to take

a lot more energy to do you can see there's a general increase in energy moving an electron from an increasingly

more positive ion like I said um so yeah okay so let's have a look at some of these now you can see

we're removing um these electrons here now these electrons are sitting in the 3s orbital remember these are the ones

furthest away from the nucleus so we're starting here these are these two electrons here these sit in the 3s if we

look along then next slot are the ones in the second shell now the second shell is much closer to the nucleus so we have

um obviously we've got six in the p orbital and two in the S orbital but this is what these electrons represent

remember we got this generally increasing shell then if we want to remove the ones from the first shell the

one closest to nucleus we're going to need to put significantly more energy in now for the exam you need to know these

jumps you need to be able to explain them so it's all about trying to take an electron for something that's closer to

the nucleus okay so we know if we look at this element here obviously we know this is

Magnesium it's because this element has 12 electrons and you can see the 12 down there there it is there

okay right first ionization Trends so we need to know about this in terms of the groups So This is Going Down group two

in particular now just to kind of quickly show you the graph first ionization energy this is the energy

required to remove one electron from each one of these elements so we start with brillium magnesium calcium

strontium barium Etc so um basically the ionization decreases as we go down the group and this is the reason why so

we've got the atomic radius as we go down the group uh gets bigger uh and the electrons become further away from the

nucleus so this means the attractive force between the outer electrons and the nucleus is weaker and this means the

energy needed to remove that electron is obviously going to be less um because it's obviously you've got a weaker Force

also shielding how many times this come up shielding is so important shielding increases as we go down the group more

shells between the nucleus in the outer shell so the attractive force is going to be weaker really important that one

uh and the energy is required to remove uh an electron decreases so we've got two things here the ionic radius and

shielding okay shielding plays a big role in here um and if we just go back to our history of the uh of the atom

this data provides strong evidence for shells remember Neils B said there were shells um and so um so this this is the

evidence that uh that would back that up but however it didn't explain data showing going across a period so this is

how we know Neil's B's model isn't quite uh not quite it's not quite the finished article okay so let's have a look at the

one when we going AC cross a period so that's going down a group okay so this is going across a period uh now

generally the ionization energy increases as we go across a period so you can see from this graph here there

it is okay you see it's generally going up I've picked um the the elements going from sodium all the way to argon just

going across a period remember periods are going along the periodic table uh and all we're doing is just taking one

electron from each one of these elements and measuring how much energy it takes now this is a bit trickier there's

your general increase Okay the reason why we have a general increase is because as we go across the period we

have one more proton compared to the previous element so this increases that nuclear attraction that we were talking

about uh shielding is similar so actually um it's still an important point we need to say that it's similar

uh in your answers um but it doesn't have any effect really um so yeah it actually marginally

decreases um so um because the uh distance from the nucleus is effectively getting a little bit smaller um but it's

not it's not significant enough um to cause too many problems in terms of energy but the shielding is similar more

energy is required to remove the electron so the ionization energy increases okay now we do have some

exceptions here and the examiners are going to pick up on these so you can see here this one and this one so we're just

going to look at what these exceptions are okay so you can see that we've got a decrease at aluminium that's the first

one that we pointed to this is evidence for having subshells okay remember this is beyond ball model so the outermost

electron in aluminium sits in a higher energy subshell slightly further away from the nucleus than the outer electron

in magnesium so um if you see here there's aluminium look 3p1 you can see magnesium doesn't have

an electron in the 3p orbital U but aluminium does now because it's a little bit further away from the nucleus and

it's slightly shielded from the 3s orbital this is going to mean that we're going don't need much energy

basically to um to remove it and it drops slightly so magnesium's out electrons in that 3s orbital so the

atomic model Neil's ball came up with didn't explain this Theory that's quite important okay right let's look at the

next one long this one's a little bit trick here this is sulfur um now there's a decrease at sulfur this is evidence

for electron repulsion this time in the orbital so um if we look at the element before which is phosphorus um phosphorus

and sulfur um they both actually have electrons in the 3p orbital so the shielding is the same so we're not

talking about shielding now um in this one the shielding is actually the same um however this is the energy diagram

for sulfur as you can see here there's the that's the setup there so we got the 3p even phosphorus phosphorus would just

have three electrons in there um so they got the same shielding but if we're removing electron from sulfur it

involves taking it from an orbital with two electrons already in it okay so there's the two electrons there now

remember what we said last time electrons in the same um uh orbital repel each other that's not very good in

terms of energy so the electrons repel so less energy is needed to remove an electron from an orbital with two in

compared to with one with phosphorus this is the configuration for phosphorus doesn't have that paired electron

therefore it takes a little bit more energy this one is paired a bit of repulsion here won't put up much of a

fight in terms of trying to take this electron so the energy drops and we don't need as much

energy okay so um that is basically it um like I say um this is just a a very brief overview of atomic structure um

these um uh these PowerPoints like I said they can be purchased um so if you just click on the link below uh in the

uh description box uh you'll be able to um access them from there if you if you would like them but uh I hope that helps

bye-bye