Lesson video

Welcome to today's lesson on isotopes.

It's part of the unit Atomic Structure in the Periodic Table.

My name's Mrs. Mytum-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'll 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 a standard nuclear notation for different elements in their isotopes.

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

On the next slide, there's some definitions for these.

If you want to read them, you can pause the video and then press play when you want to start the lesson.

Today's lesson consists of three learning cycles.

Firstly, we'll talk about isotopes, then we'll look at isotope notation, then we're going to look at property and uses of isotopes.

The first learning cycle is 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.

5.

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

So we'll 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 with 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 numbers, so 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 a 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 a 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 mass number for it, I could just add the atomic number, which is 17 plus 18 would give me 35.

So the mass 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 three, and we're gonna add to that the number of neutrons, which is four, and that's going to give us seven, 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 and 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 that 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.

Six is the atomic number and 12 is the mass number.

We've got capital O there, eight for the atomic number, 16 for the mass number.

Nitrogen, we've got seven and 14.

Manganese, we've got 25 and 55 for the mass number there.

Yttrium, we've got 39 for the atomic number and 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 three and mass number of seven.

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 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 words, so or words.

So Izzy's saying, "A different form or 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-65 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 look at 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 dash 14.

So this is the shorthand notation.

What is an acceptable shorthand notation for the isotope of boron that has an atomic number of five 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 dash 10, Ne dash 21, lowercase n, lowercase e dash 21? Pause the video now and then press play when you've got your answer.

Well done if you said neon-21 is written Ne dash 21.

The N needs to be a 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 been 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 dash 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 dash 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 mass number.

And we've got zinc.

So this time we know that the mass 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 dash 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.

We're now going to have a look at properties and uses of isotopes.

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-7 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 abundant.

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.

Isotopes 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 you got that right.

Many isotopes are radioactive, we call these radioisotopes.

Radioisotopes 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 there are modern paints used or old paints and that will tell you if the painting is an old painting or a new or fake painting.

Radioisotopes 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 track 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, it's phosphorus-32.

Here's a quick check for understanding.

Select two answers to complete the sentence.

Radioisotopes 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 mass 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 table 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 match up task for you for task C, part two.

Match up the radioisotopes to their uses.

There are two uses for each isotope.

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

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 got those.

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

Well done if you've got all those correct.

Here's today's summary.

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

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.

And isotopes have uses such as medical tracers and dating ancient rocks and artefacts.

Well done for working really hard this lesson.

I know at times this topic seems a bit tricky, however, I hope you're feeling more confident about identifying isotopes, writing notation for isotopes, and being able to identify some uses of isotopes.

Well done for working really hard.