Lesson video

- Hi, I'm Ms. Barrett from the Oak National Academy, and today's lesson is all about electronic structure and the periodic table.

This is from the Atoms and Periodic Table Unit from Key Stage 4.

Make sure you've got a periodic table with you today 'cause that's gonna really help you in today's lesson.

Let's get started.

So in today's lesson, we are going to represent electronic structures of atoms using numbers and diagrams, and explain how electronic structure is linked to the group and period number in the periodic table.

So some keywords that will help us with today's lesson.

Electrons are negatively charged subatomic particles that are located in the shells of atoms. The energy levels at fixed distances from the nucleus are called shells.

And finally, metals are substances that are usually solid, hard, shiny, and good conductors of electricity and heat.

So, the outline for today's lesson.

Firstly, we're going to have an introduction to the periodic table.

You might have come across this at Key Stage 3, but we're gonna have a little refresh on that today.

Then we're going to dive into the electronic structure, and then we're going to be linking electronic structure to the periodic table.

So, let's start with introduction to the periodic table.

So, there are 118 elements in the periodic table.

These are all the elements that we currently know exist.

There might actually be more.

So the elements are arranged into groups and periods.

So the columns marked here in blue and from one, two, three, four, five, six, seven, and zero, these are what we call the groups.

So groups are columns.

And the rows, these are called periods.

So we have seven periods altogether.

And in the middle here, we have what we call the D-block, also known as the transition metals, and these metals have some special properties, but we're not gonna go over those in today's lesson.

So each element is represented as a symbol.

Some symbols have one letter, and it always needs to be uppercase.

So here we've got hydrogen, which is an uppercase H.

And on the right here, we've got aluminium, and aluminum's got two letters, and the first letter always has to be uppercase, and the second letter always has to be lowercase.

So elements can only be one or two letters, and the first one is always a capital letter.

So on the periodic table, elements are placed in order of atomic number.

So the atomic number, the smaller number on the periodic table.

Can you remember what this actually means? Well, this means the number of protons.

So, as you go across the periodic table, each successive element increases by one proton.

So you can see here boron's got five, the next one, carbon's got six, nitrogen's got seven, et cetera.

So all the way through the periodic table, we are increasing by one proton, and protons is what determines an element.

Okay, so on the left here, I have a group from the periodic table.

Can you recognise what group that is? So elements that are in the same group typically have similar properties.

So this is group one and these are known as the alkali metals, and they're all very reactive metals.

They react with oxygen, they react with water.

And they have low density, and they're unusually soft for metals, and in fact, they're so soft that you can cut through them with a knife.

They almost feel like cheese.

So on the right here, you can see a picture of lithium and sodium, and they have the typical property of a metal, being that silvery shiny colour, but they are turning black because they're reacting with the oxygen in the air.

So the periodic table is divided into metals and non-metals by a step line.

So if you've got a periodic table with you today, I would suggest drawing this step line onto your periodic table to help you identify where the metals and non-metals are.

So to the left of this step line, these are the metals, and to the right of the step line, these are the non-metals.

So as you can see, we have a lot more metals on the periodic table than we have non-metals.

Okay, let's check how much we've understood so far.

The rows on the periodic table are called the? Is it columns, groups or periods? So that is periods.

Well done if you got that one right.

The columns on the periodic table are called the rows, groups or periods? Well, it isn't periods again, and it obviously isn't rows, so it must be groups.

The periods go across and the groups are downwards.

Try and make sure you get those the right way around.

The elements are arranged on the periodic table in order of atomic mass, atomic number or the number of neutrons? So that one is atomic number.

So remember, that means the number of protons.

So back when we first developed the periodic table, the elements were ordered in terms of mass.

But since the discovery of protons, we now realise they're actually in order of atomic number.

So every time you go up one element, that is adding one proton.

Which group is lithium in? So lithium came into a group we mentioned earlier.

That is group one.

It was one of those soft reactive metals.

Write the chemical symbol for copper.

If you need to look at your periodic table, that's totally fine.

Okay, do you think you've got it right? Let's have a look.

The symbol for copper is Cu.

So there's quite a few on the periodic table that have similar symbols.

Carbon is C, calcium is Ca, copper is Cu.

Cobalt is Co, so sometimes that gets muddled up for copper.

So make sure that you check on your periodic table to make sure you're getting that symbol right.

Okay, so our first task of the lesson.

So here, I've got a section of the periodic table, and seven elements are shown, and these are all in the correct places on this periodic table.

So you've got some questions to answer.

Pause the video, have a go and come back when you're done.

Okay, welcome back.

Let's go through the answers.

So which element is in Period 3? Well, if you look here on the third row, the only one we've got there is aluminium.

So the periods of the rows.

Which element is in group seven? So fluorine is in group seven.

Which element is in group zero? That is helium.

Sometimes group zero is called group eight, depending on where you read it, but we're gonna call it group zero.

Which two elements are non-metals? So remember, this needs to be to the right hand side of that step line.

That is helium and fluorine.

Which element is a transition metal? So remember, that is the big block that's in the middle of the periodic table.

The only one there is vanadium, V.

And then give two elements that are in the same group.

Well, the only two that we've got in the same column, so therefore the same group, is lithium and potassium, Li and K.

Give three elements that are in the same period.

So remember, periods are rows.

So this is potassium, vanadium and germanium, so K, V and Ge.

And give one element that will conduct electricity.

So basically anything that is a metal will conduct electricity.

So you could have had lithium, potassium, vanadium, aluminium or germanium.

And then which two elements differ by one proton? This is a bit of a hard one.

This was helium and lithium, because helium's number two and lithium's number three, so the difference there is that lithium has one more proton than helium.

Okay, so that's your first task done.

Really, really good job.

Let's move on to the second part of today's lesson.

So the second part of today's lesson, we are going to look at electronic structure.

So, electrons orbit the nucleus in shells, also known as energy levels, at fixed distances from the nucleus.

And you may come across the term valence electrons.

This means the electrons on the outer shell that take part in reactions.

So you can see the big black dot in the middle is the nucleus, and then you've got three rings surrounding the nucleus, and these are specific distances away from the nucleus that those electrons can reside.

So, how do we find out the number of electrons an atom has? So remember, the electron number is equal to the proton number, and this is why atoms have a neutral charge because the electrons are negatively charged, protons are positively charged, and they have an equal number of each.

So if we take helium.

Helium's atomic number is two.

Remember, the atomic number is the smaller number.

So, how many protons does helium have? Well, that must mean proton number is two for helium.

How many electrons does that mean helium has? Well, that must mean it also has two electrons.

So this would be the structure of helium, two protons, two neutrons and two electrons.

So each shell can hold a maximum number of electrons.

The shell closest to the nucleus fills first, 'cause that is at a lower energy level, and then when that shell is full, the electrons will occupy the next level or the next shell.

So here's an example.

So nucleus in the middle.

We draw our first shell, and the electrons are represented either by, you can either draw dots or crosses, it doesn't matter which one you use, but I've gone with crosses here.

And the maximum number of electrons in the first shell is two.

And in the second shell, you can fit up to eight.

And in the third shell, you can also fit up to eight.

Beyond this, it gets a lot more complicated, but at GCSE, this is as much as we need to know.

So how to draw the electronic structure of atoms. So you draw your dot to represent the nucleus, then you draw a circle around the nucleus, being your first shell, and add up to two electrons in this shell.

Then you draw a larger circle and add up to eight.

And if you've got any electrons left over because you've got an atom that's bigger, then you draw a third shell and then add up to eight electrons, like this.

So we can use numbers or diagrams to represent the electronic structure of different atoms. So I've got three different atoms here, and this one here on the very left, you can see it's got two electrons in its inner shell.

The second shell's got eight, and then the third shell's got eight.

So we can represent that as 2, 8, 8, and that's a little bit quicker than drawing out the diagrams. The middle one here, this one is 2, 8, 5.

It's got five electrons in the outer shell.

And the next one, we've got two and three.

So you can see here, if there aren't enough electrons to have a third shell, then we don't include that in the drawing.

We just draw the first two.

So as I said, above 18 electrons, the electronic structure gets a lot more complicated, and the only atoms you need to be able to draw that have more than 18 electrons are the next two.

So potassium 2, 8, 8, 1, this has 19 electrons, and calcium is 2, 8, 8, 2.

Anything beyond that, you would never be expected to draw.

Okay, so I'm gonna model how we draw an atom, and then we are gonna have a go at another one altogether.

So I'm gonna draw boron.

Boron has five electrons.

So I draw a dot in the middle to represent my nucleus, then I draw a shell, my first shell, and I draw up to two electrons, and I've still got more electrons, so I need to draw another shell, and then I can draw one, two, three, and that's my five electrons.

So that is boron.

So together, we're going to draw the electronic structure of phosphorus.

So this has 13 electrons, so this is a little bit more difficult.

So we're gonna draw a dot in the middle, and then what do we do next? So then we need to draw a shell, and this can fit up to two electrons.

Can you remember what the next one fits? Well, this one has up to eight.

So we're now up to 10 electrons now.

So we need to draw another shell, 'cause we've still got some electrons left over.

So then we draw a third shell with three electrons and that adds up to 13.

Really good job if you got that one right.

Okay, so let's see how much of that we've understood.

How many electrons does sodium have? So you might need to check your periodic table.

Pause the video if you need to.

So did you work it out? So sodium's proton number or atomic number is 11, so that must mean sodium has 11 electrons.

What is the electronic structure of sodium when represented as numbers? So you don't need to draw it out, just think about those numbers and how many electrons fit in each shell.

Okay, so this was 2, 8, 1, and that adds up to 11.

It's useful to remember that those first two shells add up to 10, so you know that if your atom is larger than 10, then there's gonna be three shells.

What is the electronic structure for this atom when represented with numbers? So have a look.

How many electrons has it got in each shell? That is 2, 8, 7.

So in that final shell, there is just one electron missing, so that must be seven.

Good job if you got that right.

What element is this atom? So this time, you're gonna have to have a look at the electrons and match it up to something in the periodic table.

Okay, so the element that is 2, 8, 7 is chlorine.

Give the electronic structure of carbon, which has six electrons, using a diagram and numbers.

You might wanna pause the video here to have a go at this one.

Okay, so for six electrons for carbon, electron, sorry, nucleus in the middle, a shell with two electrons, and we've got four more electrons, so that must be in the second shell.

So this one is 2, 4 for carbon.

Good job if you got that one right.

Okay, so onto your second task for this lesson.

So what you're going to do is complete the electronic structures for the first 10 elements.

So here, I've drawn a table in the same layout as the periodic table, and I've included some elements in there already.

So I've got hydrogen, carbon and neon.

You need to fill out the rest, just like I've done, so the name, the electronic structure, and the electronic structure represented as a number.

And then answer the question, what is the electron pattern as you go across the period? Pause the video, good luck and I'll see you when you get back.

Okay, how did you get on? So let's go through the answers.

I'm gonna show you the completed table, and you just need to check that you've got your answers right.

So if you need to pause it, that's absolutely fine.

So there we go.

So the next one was helium, then we've got lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, and neon.

And then you just need to make sure that your electronic structures are right.

So the pattern that you've probably identified as you were doing this is as you go across the period, one electron is added each time.

So this is the same pattern as the protons as well, and that's because remember, the protons are equal to the electrons.

So as you go across the period and you go to the next element, one electron is added and also one proton is added.

If you've got those right, then give yourself a really, really big pat on the back.

Well done.

Let's move on to the final part of the lesson.

So the next part, we are going to be linking the electronic structure that we've just talked about and the periodic table that we spoke about at the start.

So here, I've got three elements.

I've got helium, beryllium, and magnesium.

How many shells does each element have? Have a think, have a look.

So helium has one shell, beryllium has two shells, and then magnesium has three shells.

Next question, which period is each element in? So if you need to have a look at your periodic table, and have a look where these elements sit on the periodic table.

Helium is in period one, beryllium is in period two, and magnesium is in period three.

So are you starting to notice a pattern? So the element's period tells you how many shells the element has.

So if we have a look at the periodic table, how many elements are there in each of the first three periods? Well, in the first period, we've got hydrogen and helium, there is only two.

And in the second period, we've got one, two, three, four, five, six, seven, eight.

And then the third period, we've also got eight.

So does that look familiar? So this was the rule that we spoke about earlier, our 2, 8, 8 rule for filling up with electrons.

So as you can see here, a new shell means a new period on the periodic table.

So I've got some other elements here.

I've got lithium, beryllium, boron, and carbon.

How many electrons does each one have in the outer shell? So have a little look.

How many are in the outer shell? Well, lithium's got one electron in the outer shell.

Beryllium has got two electrons in the outer shell.

Boron's got three and carbon's got four.

Which group is each element in? Have a look at your periodic table if you need to.

So lithium's in group one, beryllium in group two, boron's in group three, and carbon's in group four.

So here's another pattern.

So the number of electrons in the outer shell is equal to the group number.

So elements that have a full outer shell, these are the ones that we call the most stable, or we can call them unreactive.

So this is because they don't need to react with anything else to fill their outer shell.

When chemical reactions are going on, all elements are trying to do is fill up that outer shell and become stable.

So here we've got helium, neon, and argon.

All of these elements have a full outer shell.

Which group are these three elements in? So these are all in group zero, and the reason why they're called group zero and not group eight is because, although the group number normally matches the outer electron number, well, helium's only got two, it doesn't have eight, so if we call it group eight, that wouldn't quite make sense.

So it gets called something different.

We just call this one group zero.

So elements that don't have a full shell will react with other substances to form chemical bonds to gain a full outer shell and become more stable.

So here I've got hydrogen, which has one electron in the outer shell.

And here I've got fluorine, and this has seven electrons in the outer shell.

How many are both of them missing? Well, hydrogen's missing one.

It needs two for that first shell.

And fluorine's missing one as well, because that one needs eight in that shell.

So this is what happens.

They bond together to form hydrogen fluoride, and they share one of their electrons so that now, both of those have a full outer shell, and that's what we call a chemical bond.

And that molecule is much more stable than hydrogen and fluorine are.

So elements that are in the same group have the same number of electrons in their outer shells, and this is why hydrogen technically belongs in group one, despite its differing properties.

And that's why elements that are in the same group will usually have similar properties.

So for example, they usually react in similar ways.

So group one that we spoke about earlier with lithium, sodium and potassium, the alkali metals, they're all very reactive.

And for example, all three of those will react violently with water, and that's because they all have this one electron in their outer shell.

Right, so lots of new information there.

Let's see how much we can remember.

So which element has two shells and five outer electrons? If you want to pause your video and have a look at your periodic table, that's absolutely fine.

So the element that has two shells and five outer electrons is nitrogen.

So this one was in period two and in group five, so that must be nitrogen, which looks like this.

Which element has three shells and one outer electron? So this time, we need to look on the period three and group one.

That was sodium.

Sodium looks like this.

How many shells and how many outer electrons does bromine have? So have a look where it is in the periodic table.

So bromine has three shells and seven outer electrons.

It's in group seven and in period three.

How many shells and outer electrons does magnesium have? Magnesium has two shells and two outer electrons.

It's in group two and in period two.

All right, let's move on to your last task for this lesson.

So the first part, you need to fill in the blanks.

So read through the paragraph and then put in the correct word into the space.

Pause the video and come back once you're finished.

Okay, how did you get on? Let's go through the answers.

So elements that are in the same group have the same number of electrons in their outer shell.

Elements in the same period have the same number of shells, and the most stable atoms have a full outer shell.

Chemical reactions take place so elements can complete their outer shell by forming chemical bonds.

So if you've got those right, really, really well done.

Let's move on to part B.

So in this section, you are going to complete the table.

So we've got six different elements here, and you need to fill in the number of electrons, give the electronic structure as a number, number of shells, number of outer electrons, the group number, and the period number.

Pause the video and come back once you've finished that.

Okay, how did you get on with that? So, I'm gonna show you the answer, so you just need to check your table and give them a tick if you've got those right.

If you got any wrong, make sure you correct them.

So calcium has 20 electrons.

The electron structure is 2, 8, 8, 2.

It's got four shells because it's in period four.

It's got two outer electrons and that means it's in group two.

So just check the rest of the answers.

I will give you a second to have a look through.

So that is the end of the tasks for today, so a really, really big well done.

You've worked really hard in this lesson.

So to summarise, the periodic table arranges all known elements into periods and groups.

Electrons are arranged in shells.

The first shell occupies two electrons, the second has eight electrons, and the third has eight electrons.

Electronic structure can be represented using diagrams or numbers, and the number of outer electrons tells you the group number, and the number of shells tells you the element's period number.

So that is all for today.

A really, really big well done for getting through that lesson.

Have a go at the exit quiz and see how much you've learnt.

Thank you for using the Oak National Academy and I will see you next time.