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Welcome to today's lesson on isotopes and relative atomic mass.

It's part of the unit atomic structure in the periodic table.

My name's Mrs. Mitem-Smithson, and today's lesson's all about isotopes.

Don't worry if you don't know anything about it.

We're going to go through this lesson step-by-step and you'd be more confident by the end of the lesson about what isotopes are.

By the end of today's lesson, you should be able to write and use the standard nuclear notation for different elements in their isotopes and also calculate relative atomic mass using isotope masses and abundances.

Here are today's keywords, isotope, proton, neutron, mass number, relative atomic mass.

On the next slide, there's some definitions for these keywords, so pause the video if you wish to read them and then press play when you're ready to start the lesson.

Today's lesson consists of four learning cycles.

Firstly, we're going to do about isotopes, then isotope notation followed by properties and uses of isotopes and finally relative atomic mass.

So first of all, we're going to do about isotopes.

So let's get learning.

On your periodic table, there are some elements that have a relative atomic mass number that's not a whole number.

So the two examples are chlorine, which has got a relative atomic mass number of 35.

5 and copper, which has got a relative atomic mass number of 63.

Isotopes are the reason for the relative atomic mass number not being a whole number.

So we have a look at what an isotope is.

So an isotope is a different form of an atom of the same elements.

It's got the same number of protons 'cause each element has a specific number of protons, but it's got a different number of neutrons.

Let's have a look at two examples.

So here we've got carbon-12 and carbon-13.

You can see that they've got different mass numbers.

Here's carbon-12.

It's got six protons, six electrons and six neutrons, and then we have a look at carbon-13.

Carbon-13 has got six protons, six electrons and seven neutrons.

So the difference between carbon-13 and carbon-12 is that carbon-13 has got an extra neutron than carbon-12.

A quick check for understanding now, an isotope is a different form of an atom of an element that has the same number of protons but a different number of, is it protons, electrons or neutrons? Pause the video now for some thinking time and press play when you've got your answer.

Well done, if you said neutrons, the only thing that's different in an isotope is that they have a different number of neutrons.

Well done if you got that one right.

Here's a quick check for understanding, the number of neutrons in an isotope affects the atomic number, the mass number or both the atomic number and the mass number? Pause the video for some thinking time.

Press play when you've got your answer.

Well done, if you said that it only affects the mass number, so the atomic number just tells you the number of protons and the number of protons between isotopes is always the same, it's only the mass number that changes.

Well done if you got that correct.

I've got a quick check for understanding for you now, which are the isotopes of nitrogen.

Pause the video for some thinking time and press play when you've got your answer.

Well done, if you said A and B.

A and B are the isotopes of nitrogen, they have the same atomic number to the same number of protons, which is seven, but they've got a different mass number because nitrogen-15 has got one more neutron than nitrogen-14.

Well done if you got that correct.

To represent isotopes of elements, we use something called the standard nuclear notation and this shows a chemical symbol, the mass number, and the atomic number of the element.

So here's our example.

So we've got the element symbol, the general one is X, and the specific example that we're looking at today is nickel, so we've written Ni.

and then we're going to look at the atomic number.

So that's the smaller of the two numbers and that is represented by a Z in the general nuclear notation and 28 because that is nickel's number of protons.

Then we've got the mass number here, so that's represented by an A in the general standard nuclear notation and it's 59 for nickel.

A quick check for understanding which shows the general standard nuclear notation? Pause the video for some thinking time.

Press play when you've got your answer.

Well done if you said C, that's absolutely right.

We've got the element symbol represented by an X, the atomic number, which is Z, and the mass number, which is A.

Well done if you got that correct.

Here's a quick check for understanding which shows the mass number? So we've got three letters circled, which one's the mass number.

Pause the video now for some thinking time, press play when you've got your answer.

Well done if you said A.

A represents the mass number.

Which represents the atomic number? So we've got three circled again, which shows the atomic number? Pause the video for some thinking time, press play when you've got your answer.

Well done If you said B.

B shows that Z represents the atomic number.

The mass number tells you the total number of subatomic particles in the nucleus of an atom.

So the atomic number tells you how many protons are in the nucleus and then we can look at using this equation, so mass number equals atomic number plus number of neutrons.

So this chlorine isotope has got 18 neutrons.

So if I wanted to find out the math number for it, I could just add the atomic number, which is 17 plus 18 would give me 35.

So the math number for this chlorine isotope is 35.

What I want you to do is calculate the mass number for the following atoms. So we've got lithium and this lithium isotope has got four neutrons and we've got iron and this iron isotope has got 30 neutrons.

Pause the video now and then press play when you're ready for the answer.

Well done for completing that task.

You can see the mass number for lithium.

So we're going to take the atomic number, which is 3, and we're gonna add to that the number of neutrons, which is 4, and that's going to give us 7, which is the mass number for iron.

We're going to have 26, which is the number of protons.

Add to that, the number of neutrons, which it tells us in the question got 30, gives a mass number of 56.

So well done if you've got those two correct.

Here's part one of task A, using your periodic table in the equation below, write the standard nuclear notation for the following isotopes.

And we've got the equation mass number equals atomic number plus number of neutrons.

So the first column here, we've got the element and the mass numbers given, and the second column there we've got the element name and we've got the number of neutrons given.

So pause the video, complete the task, and then press play and we'll go through the answers together.

Well done for completing that task.

Let's see how you got on.

So here's carbon.

So it's got to be a capital C.

Remember 6 is the atomic number and 12 is the mass number.

We've got capital O there, 8 for the atomic number, 16 for the mass number nitrogen we've got 7 and 14 manganese, we've got 25 and 55 for the mass number there yttrium we've got 39 for the atomic number 89 for the mass number.

Remember it should be a capital Y for manganese, you need a capital M and a lowercase n, otherwise you don't get it correct.

Then we've got lithium, which has got an atomic number of 3 and mass number of 7, arsenic which is 33 and 75, tungsten 74 and 184, iodine 53 and 127 and bromine 35 and 80.

Well done if you've got all of those correct.

The students have been discussing isotopes with Laura.

What I want you to do is help Laura write a definition to explain what an isotope is.

So here's Laura and her sentence starter is an isotope is, and then the students have got some suggestions for her.

Want you to choose the correct word, so, or words.

So Izzy is saying a different form of the same form of an atom of the same element.

Alex is saying, which has the same or a different number of protons.

And Sophia's gonna finish off the sentence, but the same or a different number of neutrons.

So once you've written that, you should have a nice definition.

So pause the video now complete the task, press play when you're ready and we'll go through the answer.

Well done for working really hard.

Let's see if your answers matches up with Laura's.

So you should have a definition written for an isotope and it should read this.

An isotope is a different form of an atom of the same element which has the same number of protons but a different number of neutrons.

So well done if you got that correct.

Here's part three of task A.

There are three isotopes of neon for you to identify, explain your choices and why the other one is not an isotope.

Pause the video, complete the task and press play and we'll go through the answers together.

Well done for working hard and completing the task.

If you spotted that these were the three isotopes of neon, well done.

So they've got the same number of protons if you look.

So they've all got 10 protons and they've got different mass numbers so they're showing.

So neon-20 has got 10 neutrons, neon-21 has got 11 neutrons, neon-22 has got 12 neutrons.

And here's another reason.

So this one is not an isotope of neon because it's got a different number of protons.

So this element would actually be sodium and not neon.

So well done if you've managed to do that.

Here's part four of task A.

Copper has got two isotopes.

Compare the similarities and differences between the two isotopes and you need to talk about protons, electrons and neutrons.

Pause the video, write your answer and then press play and we'll go through the answers together.

Well done for completing part four of task A.

What we're going to do, first off, we're going to calculate the number of protons.

So in copper-63 got 29 protons, copper-65, 29.

Electrons, 29 electrons 29, and the neutrons, we've done a calculation there to calculate the number of neutrons.

So we've got copper-63 has got 34 and copper-5, we've got 36 neutrons.

Then all we've got to do is say what's the same and what's different.

So they've both got 29 protons, that's the same number.

They've both got 29 electrons that's the same number, but they've got a different number of neutrons.

So copper-63 has got 34 neutrons and copper-65 has got 36 neutrons.

It's got two more.

So well done if you managed to get all of that correct, you've done really well.

We've completed our first learning cycle of isotopes.

Now we're going to move on to isotope notation.

Scientists have developed a shorthand way of writing an isotope and it is as follows, it includes the element name or chemical symbol followed by the mass number of the isotope.

So this is different to the relative atomic mass number found on the periodic table.

It's important for you to remember that.

So here's our example and here's how we could write it.

So we could write carbon-14, so carbon followed by a little dash or a hyphen 14, or we could write it the element symbol.

So that would need to be a capital C-14.

So this is the shorthand notation.

What is an acceptable shorthand notation for the isotope of boron that has an atomic number of 5 and a mass number of 10? Is it boron-5, boron-10 or boron-15? Pause the video for some thinking time.

Press play when you've got your answer.

Well done, if you said boron-10, remember it's the mass number that we put after the element name or symbol.

Here's another check for understanding what is an acceptable shorthand notation for the isotope of neon that has an atomic number of 10 and a mass number of 21.

Is it Ne-10, Ne-21, lowercase n lowercase e dash 21? Pause the video now and then press play when you got your answer.

Well done, if you said neon 21 is written Ne-20, that n needs to be capital N because it's the chemical symbol found on the periodic table.

So well done if you got that correct.

Now here's our task, task B, complete the table.

So the first row's being done for you.

So we've got the element name iron, the element symbol Fe, the atomic number which is 26 and the mass number.

And what I want you to do, you can complete the isotope shorthand notation, so we've got it in words.

So that's the name iron-54 because it's the mass number or we've got the shorthand notation using the symbol which is Fe for iron dash 54.

Pause the video now complete the table and then press play and we'll go through the answers.

Well done for completing Task B.

I hope you found it quite straightforward.

So I've completed the first row for you for iron, let's have a look at copper.

So copper's got an atomic number of 29 and a mass number of 63.

So the shorthand notation, the word version, would be copper-63.

It doesn't matter if copper has a capital or a lowercase C for that one, however, it does matter when we're looking at symbols.

So the element symbols should always be a capital followed by a lowercase.

So in this case we've got Cu and then dash 63.

So capital C, lowercase u dash 63 for the math number.

And we've got zinc.

So this time we know that the math number is 68 because we can read that back from the shorthand notation and then we can find out the symbol on the periodic table, which is Zn, capital Z, lowercase n, dash 68.

Well done if you got that one.

Then we've got selenium that's got a mass number of 80, and if we're going to write that out fully, it should be selenium-80.

Now we've got selenium written again, however, if you have a look, this is a different isotope.

So this is selenium-78, so this would have a mass number of 78 and the shorthand we would write capital S, lowercase e dash 78.

And then finally for krypton we've got a mass number of 84, which means that we should be writing krypton-84 for that one.

So well done.

If you've got all of those correct, you've done really well with that task.

We've now completed our first two learning cycles of isotopes and isotope notation.

Now we're going to have a look at our third learning cycle of properties and uses of isotope before moving on to relative atomic mass.

Isotopes of an element will have the same chemical properties as each other.

They will react in the same way with different chemicals because all isotopes have the same number of electrons.

So because it's the electrons that dictate the chemical properties because all isotopes of the same number of electrons, that's why they've got the same chemical properties.

So you can see in this picture here, for example, hydrogen-1, hydrogen-2, and hydrogen-3, will all burn explosively with oxygen.

So they've all got the same chemical properties.

Here's a quick check for understanding, lithium-6 reacts vigorously with water.

What would happen with lithium- when placed in water? Would no reaction take place with lithium-7 and water? Would lithium-7 be more reactive than lithium-6 or would lithium-7 react in the same way as lithium-6? Pause the video now and press play when you've got your answer.

Well done if you said that lithium-7 would react in the same way as lithium-6, that's because they've got the same number of electrons and that's what dictates the chemical reactivity of an element.

So well done if you got that correct.

Here's another check for understanding which two isotopes have the same chemical properties, is it selenium-80, selenium-74, germanium-73, arsenic-73? What I want you to do is select two of them and tell me which ones of those two have got the same chemical properties.

So pause the video for some thinking time, then press play when you've got your answer.

Well done, if you said that selenium-80 and selenium-74 would have the same chemical properties because they're the same element.

So the same elements have got the same chemical properties because they've got the same number of electrons as each other, just a different number of neutrons.

So well done if you got that correct.

All elements are a mixture of isotopes.

The mass number on a periodic table is a relative atomic mass.

So the RAM relative atomic mass of an element compared with carbon-12.

Isotopes are the reason why the mass number is not always a whole number on the periodic table.

Usually there'll be one isotope of an element that's got a greater abundance, so that's a greater quantity or proportion than the other isotope or isotopes of that element.

So if we have a look at neon and we have a look at their abundances, you can see that over 90% of neon exists as neon-20, a tiny little bit of it, so 0.

27% exists as neon-21 and 9.

25% of neon is neon-22.

So if you added all those up, it would add up to 100%, but most of neon is made up of neon-20 that has the greatest abundance.

A mean relative atomic masses calculator that takes into account the abundance of the isotope.

So it takes into account the amount of each one of those isotopes, the proportions of them, and this relative atomic masses quoted on the periodic table.

It's usually rounded up to the nearest whole number.

So here's neon.

If you work out the relative atomic mass of these, you'll round it up and that will be 20.

So that's what's quoted on the periodic table, but there are exceptions for chlorine and copper which are quoted to the near 0.

So chlorine has got a relative atomic mass of 35.

5 and copper has got a relative atomic mass of 63.

True or false isotopes are the reason the relative atomic mass number is not always a whole number? Is that true or is that false? Pause the video for some thinking time and come back when you've decided if it's true or false.

Well done if you say that that was true, isotope are the reason that the relative atomic mass number is not always a whole number.

Let's justify your answer.

So the periodic table shows the mean atomic mass of the different quantities of isotopes of an element, or does the periodic table show the mass of the isotope with the highest percentage abundance? Pause the video now and then press play when you've got your answer.

Well done, if you said it's A, the periodic table shows the mean atomic mass of the different quantities of isotopes of an element.

Well done if got that right.

Many isotopes are radioactive.

We call these radio isotopes.

Radio isotopes can be used as radioactive traces in medical procedures.

So during operations or if you want to find out some more information about a patient and they can find tumours or diseases, for example, heart disease by using these radioactive tracers.

Or sometimes they can be used to authenticate paintings to check if they're fake or not.

So old paintings use old pigments to create the colours and they can check these to see if they are modern paints used or old paints, and that will tell you if the painting is an old painting or a newer fake painting.

Radio isotopes are also used to preserve food.

So to make it last longer in the supermarkets and in your fridges at home.

You can sterilise medical equipment with it.

So you can kill off pathogens such as bacteria and viruses.

And you can also determine groundwater resources.

So where the water's coming from or going to.

Carbon-14 is one of the most useful isotopes that scientists use.

It can be used to date some fossils and ancient artefacts accurately.

So for example, the contents of a canopic jar that they've got from some Egyptian tomb or maybe a fossil in amber could be used to find out how old that creature is.

Phosphorus-32 is another isotope and this can be used to the uptake of fertiliser in plants from the roots to the leaves.

So if you want to know how fast it's going or where it goes within the plant, you can use this phosphorus-32 isotope.

It can also be used to detect ovarian and other cancer cells.

So here's some plants here being grown.

If we wanted to track that fertiliser, that'd be good.

We could use this phosphorus-32.

And we could also identify things like these tumours here, which are ovarian and other kind of cancers.

So it's very useful, this phosphorus-32.

Here's a quick check for understanding, select two answers to complete the sentence.

Radio isotopes have many uses including, dating ancient artefacts, detecting tumours, they're used as a fertiliser for plants or to make fruit and vegetables taste better.

Pause the video now for some thinking time, press play when you've got your answer.

So well done, if you said that they are used for dating ancient artefacts and also detecting tumours, well done if you've got those two uses correct for radioisotopes.

Radioisotopes are used for many different purposes.

Select two from the list.

Are they used to preserve food, to preserve metal, to sterilise medical equipment or to manufacture glass? Select two of those.

So pause the video once you do that and press play and we'll look at the answers.

Well done If you said that they are used to preserve food and also to sterilise medical equipment.

I've got a true or false for you, now.

Phosphorus-32 can be used for tracking the movement of fertilisers in plants.

Is that true or is that false? Pause the video while you decide, then press play, and I'll tell you if you're right.

Well done If you said that phosphorus-32 can be used for tracking the movement of fertilisers in plants.

That was true, now I want you to justify your answer.

So is it that phosphorus-32 can be used to track how phosphorus moves from the roots to the leaves in plants? Or is it it can be used to track how carbon dioxide moves from the roots to the leaves in plants? Pause the video now.

Have a little think and press play when you've got your answer.

So well done, if you said a phosphorus-32 can be used to track how phosphorus moves from the roots to the leaves in plants.

Here's part one of task C, help Laura to explain why the math number on the periodic table isn't always a whole number.

So she's written a sentence starter for you.

The mass number on the periodic for an element is not always a whole number because, and then I want you to pause the video, complete the task and press play when you've got your answer.

Well done for completing that task.

Let's see if your answers match mine.

So the mass number on the periodic table for an element is not always a whole number because there are different abundances of isotopes of an element.

A mean relative mass.

So a relative atomic mass is calculated and the relative atomic mass is usually rounded to the nearest whole number to put on the periodic table.

So well done, if you've got answers similar to these.

I've got a matchup task for you for task C, part two, match up the radio isotopes to their uses.

There are two uses for each isotope.

So here's the isotopes carbon-14, phosphorus-32 or all other radio isotopes.

And here are the uses, finding out how old some fossils are, finding out how fast fertilisers move through plants, making fruit and vegetables last longer.

Finding out if someone has ovarian cancer.

Finding out how old ancient artefacts are, for example, how old an Egyptian mummy is or sterilising surgical equipment.

So pause the video, complete the task, and then press play and we'll go through the answers together.

Well done for completing part two of task C.

Let's see how you got on.

So carbon-14, you can find out how old some fossils are.

If you remember we had that picture of that fossil in amber and also how old ancient artefacts.

For example, you could find out how old an Egyptian mummy is.

Phosphorus-32, you can find out how fast fertilisers move through plants and you can also find out if someone's got ovarian cancer.

Well done if you've got those.

And other radio isotopes making fruit and vegetables last longer and sterilising surgical equipment.

Well done, if you've got all those correct.

You've worked really well this lesson, completing three learning cycles already.

So we've looked at isotopes, we've looked at their notation, we've looked at their properties and uses, and now we're going to look at the relative atomic mass.

Some elements are made up of mainly one abundant isotope with very small quantities of other isotopes, whereas some elements are made up of more than one abundant isotope.

So let's have a look.

Here's an example.

So here's chlorine.

75% of chlorine is chlorine-35, which means that 25% of chlorine is chlorine-37.

True or false, the abundance of an isotope is split equally between the number of isotopes.

Is that true or is that false? Pause a video for some thinking time.

Press play when you've got your answer.

Well done if you said that that was false.

So let's justify your answer.

Isotope abundances vary from element to element or an element with two isotopes will always be made up of 50% of each isotope.

Pause the video now, think about your answer.

Press play when you're ready and I'll tell you if you were right.

Well done if you said isotope, abundances vary from element to element, it's not split equally 50% of each isotope.

If you've got two isotopes, it varies from element to element.

Well done if you've got that correct.

The relative atomic mass, sometimes written a subscript r of an element is the mean mass of its atoms taking into account their abundances compared to one 12 the mass of a carbon-12 atom.

This sounds really difficult and very complicated, but we're just looking at the mean of the mass of the atoms and we're just taking into account how much of each one of those isotopes there are.

So most of the relative atomic numbers for elements on the periodic table are rounded to the nearest whole number.

There are two exceptions.

Chlorine which is 35.

5 and copper, which is 63.

Some periodic tables quote the relative atomic mass to the nearest one decimal place.

I've got a quick check for understanding the relative atomic mass of an element is the mean mass of its atoms taking into account their abundances compared to one 12th, the volume of a carbon-12 atom, one 12th, the mass of a carbon-12 atom, half the mass of a carbon-12 atom or one 12 the mass of an oxygen-12 atom.

Pause the video for some thinking time.

Press play when you've got your answer.

Well done If you said B, the relative atomic mass of an element is the mean mass of its atoms taking into account their abundances.

We're gonna compare that to one 12th the mass of a carbon-12 atom.

The relative atomic mass is sometimes given the symbol A subscript r, and this is quoted on the periodic table and it's calculated using the following equation.

So this equation looks far more complicated than it actually is.

So this is the sum, this funny little E, it's a Greek letter means sum means add them all together of the relative mass of each isotope, multiplied by the percentage abundance of each isotope divided by the sum of the isotope abundance.

Now what's quite easy about this is if the abundances are given as a percentage, this number here, the sum of the isotope abundance is always 100.

So here's an example that we're going to work through.

So we've got two isotopes of chlorine, chlorine-35, which has got 75% abundance.

So that means that there's 75% of it is chlorine-35, the other 25% of it is chlorine-37.

So all we've got to do now is put these numbers into this equation.

So we've got our first isotope and the relative mass of that is 35.

We are going to multiply that by its abundance, which is 75%.

So we're going to write 75.

And then what we're going to do is we're going to add that to the other isotope.

So that's chlorine-37 multiplied by 25 because we've got a 25% abundance of that.

So you're going to work out those numbers in brackets first.

Then you're going to add them together and we're going to divide that by 100 because remember it's always 100%.

So it's always 100 when abundance are given as percentages.

Then all we've got to do is use our calculators to calculate it and that will come out at 35.

So the Ar, the relative atomic mass for chlorine is 35.

So well done if you've managed to follow that, we're gonna have a little practise on the next slide.

Here's another example, calculate the Ar.

So the relative atomic mass for copper to one decimal place.

So here's our isotopes copper-63 and the abundance of that is 69.

2%.

Then we've got another isotope of copper, 65, so that's copper-65 and that's got an abundance of 30.

8%.

We're going to write down our equation.

So this is the equation that we looked at before.

All we've got to do now is put our numbers in.

So we've got copper 63, so we're going to do 63, we're going to multiply that by the abundance and then we're going to add that to the other isotopes.

So that's 65 'cause it's copper-65.

Going to multiply that by 30.

8 'cause it there's 30.

8% abundance of copper-65.

Then we're going to add those together and we are going to divide them and by 100 because that is a percentage.

So as it's given as a percentage, the sum of the isotope abundance is always 100.

And that answer should come out at 63.

So that means that the Ar for copper is 63.

What I'd like you to do now is have a go.

So calculate the Ar for gallium to one decimal place.

What I want you to do is use that information in the table about gallium and calculate the relative atomic mass.

So the Ar for gallium, just follow the steps that I did and you won't go wrong.

Pause the video now complete this little task and then press play when you've got your answer.

Well done for having a go at this calculation.

I'm sure you found it straightforward.

So all you've got to do here is follow it.

So gallium-69.

So 69 multiplied by the abundance of it.

So that's 60.

Add that to 71 'cause we've got gallium-71 multiplied by 39.

9, we're going to divide that by 100 because the isotope abundance is given in a percentage and when we calculate that out we should get 69.

So well done if you've managed to get 69.

8, the Ar or the relative atomic mass for gallium is 69.

Now I've got a task for you.

So I've got part one of task D.

I want you to use the equation and the information in the table below to explain why boron has got a relative atomic mass of 10.

8 on the periodic table.

So here's the equation you need to use and the table of information, I want you to calculate the Ar or the relative atomic mass.

So pause the video whilst you do that, write out all your workings out and then when you've completed this press play and we'll see if you're correct.

Well done for completing part one of task D, I hope you've managed to do okay.

So boron-10.

So we've got this equation here which says that sum of the relative mass of each isotope multiplied by the percentage of abundance of each isotope.

So we've got boron-10, so that's 10 multiplied by 19.

Then you need to add that to 11 because that's the second isotope of boron and there's 80.

1% of that isotope.

So you're going to do 11 times 80.

1 and you're going to divide all of that by 100, and you should get an Ar or a relative atomic mass of 10.

Well done if you've got that correct.

Now to practise a little bit more, I've got part two of task D, use equation and information from the table below to calculate the Ar.

So the relative atomic mass for bromine and iron.

So there's the equation.

So you've got your information for bromine and then you've got your information for iron.

So I'm looking for two answers here.

Pause the video once you complete this task and press play when you've calculated the Ar for bromine and the Ar for iron.

So well done if you've managed to complete this task.

Here's the calculations for bromine.

So for bromine we've got bromine-79.

So it's 79 multiplied by 50.

7 because there's 50.

7% abundance of bromine-79, add that to 81, that's a second isotope of bromine.

So we've got bromine-81 and there's multiplied that by 49.

3 because it's 49.

3% abundance.

Divide all of that by 100.

So use your calculator for this and then you should have come out with 80.

So 80.

0 is your answer for the Ar or the relative atomic mass of bromine.

Now we're gonna go through the next one.

So here's the second one that we're going to look at, now, we're going to look at calculating the Ar for iron.

So this time iron's got four isotopes, four different isotopes.

So all we've got to do for each one, so take each one in turn 54, 'cause that's iron-54, multiply that by 5.

8, that's the abundance of iron-54.

We're going to add that to iron-56 so 56 multiplied by 91.

We're going to do the same again for iron-57.

So we're going to have 57 multiplied by 2.

And finally we're going to add on to that 58 'cause it's iron-58 and we're going to multiply that by 0.

3 and we're going to divide all of that by 100 and that should give us our answer of 55.

So the Ar, so the relative atomic mass for iron is 55.

Really well done if you've managed to get all of that correct.

Here's the summary for today's lesson.

Atoms of many elements vary in the exact number of neutrons in their nucleus and each version is called an isotope.

Existence of isotopes results in relative atomic masses of some elements not being whole numbers.

Standard nuclear notation shows the chemical symbol, the mass number, and the atomic number of the isotope.

The relative atomic mass of an element is an average value that takes into the account the abundance of the isotopes of the element.

Well done for working really hard during this lesson.

I know at the at the end those calculations seemed complicated, but when we work through them step-by-step, I'm sure you were getting the hang of them by the time it came to this last one.

So well done for being very knowledgeable about isotopes, their uses and how to calculate the relative atomic mass.

I've finished the video