Lesson video

- Hi folks.

My name's Mrs. Farrow.

For today's session you're gonna use a pen and a piece of paper so it's a good idea to put your mobile devices on silent or switch them off to help to avoid any distractions.

If you need to take a moment to sort that, then please do so now and press play when you're ready to resume.

Today's lesson is about the development of the periodic table.

We want to have a look at how the elements have been arranged, taking a look at some of the different properties the elements have and how the periodic table has changed over time as our knowledge of these properties and the particles that make up the elements have changed.

Some of the key words that you might spot as we go through today's session include: Properties, these the characteristics of a substance.

They're used to describe and identify substances and it has been used to sort the elements into the correct groups within the periodic table.

The periodic table, this is an arrangement of all of the elements based on their atomic number and properties and an element, an element is a substance made from just one type of atom.

We've broken today's lesson about the development of the periodic table down into three cycles today.

First, looking at what are properties? Second, focusing on the early periodic table and how it changed over time.

And then lastly, the modern periodic table.

So if you're ready, we'll get started and take a look at what are properties.

Well properties is a phrase that we use to describe the characteristics of a substance.

Properties tend to fall into one of two groups.

Substances either can show chemical properties or physical properties.

Chemical properties include things like reactivity, so if an element reacts with water or oxygen, for example.

We also have flammability.

Flammability is similar to reactivity in that burning is a chemical reaction.

The ease with which something catches fire is described as its flammability.

Acidity, that describes whether the substance is behaving like an acid or an alkaline in reactions, and toxicity describes whether it is poisonous to living things.

Physical properties that we might use to describe a substance are things like the colour.

Density, this is the mass per given volume.

If something has a lot of mass in a set volume, then it's going to be dense and more likely to sink in water.

If something has very little mass per given volume, then it's going to be less dense and more likely to float on water.

We can also describe a substance's hardness, so if is strong or brittle and we can look at the melting and boiling points.

These are the temperatures at which physical changes take place.

Melting being changing from a solid to a liquid, and boiling when a substance changes from liquid to gas.

So let's do a quick knowledge check.

Which the following is a physical property of substances? Is it A acidity, B density, or C flammability? The correct answer is B density.

The other two listed here are chemical properties.

Which two of the following are chemical properties of substances? You can choose from A toxicity, B hardness, C acidity and D colour.

The correct answers are A toxicity and C acidity, toxicity describing how it affects living creatures and whether it is poisonous or not, and the acidity describing whether it behaves as an acid or alkaline within chemical reactions.

Now it's time for you to have a go at a practise task.

We would like you to define the term property and then reading through the list, circle the chemical properties and underline the physical ones.

You'll need to give yourself a little bit of time to complete this task and give it your full attention.

So we suggest you pause the video now and press play when you're ready to hear the correct responses.

How did you find it? Let's take a look at how you got on.

So the first task asks you to define the term property.

Now you don't have to have word for word exactly what I've written but your answer should follow the same general themes.

Property is the physical or chemical characteristics of a substance, allows us to describe and identify it.

Part B asks you to circle the chemical properties and underline the physical ones.

So let's take a look.

Reactivity, this is how the substance reacts with either oxygen or water or other elements.

And so this is a chemical property.

Colour is a description of the physical appearance and so should be underlined as a physical property.

Flammability, a description of how readily something catches fire which is a chemical reaction and so should be circled.

Hardness, how likely something is to break or how strong it is, is a description of its physical qualities, and so should be underlined.

Acidity describes whether it behaves as an acid or alkaline within chemical reactions and so is a chemical property that should be circled.

And lastly, we have melting point.

Melting is the physical change from a solid to a liquid and so this should be underlined as a physical property.

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

If not, don't worry, you can always go back and have a look at this first section of the video again.

So we've taken a look at what are properties and properties are important as they played a key role in the ordering of the elements in the early periodic tables.

So let's take a look at who and how the elements were ordered in the beginning and how it has developed over time to become the periodic table that we know and secretly love today.

So the first scientist to contribute to ordering the elements within the periodic table was somebody called John Newlands in 1863.

Newlands spotted a pattern.

He found that if he wrote the elements in order of atomic weight that each of the eighth elements had very similar chemical properties and behaved in similar ways when he reacted them with oxygen and water.

He referred to this as his Law of Octaves, and we can see here from the image, that Newland's work enabled the early formation of some of the groups that we see today.

Li for lithium, Na for sodium, and K for potassium, all being in the same column because they had very similar properties.

This forms Group 1 of the modern periodic table today.

The third column within Newland's table also has beryllium Be, magnesium Mg and calcium Ca.

This forms Group 2 of the modern periodic table today or the beginning of it anyway because they all show similar chemical properties during reactions.

So Newlands' work was incredibly useful at identifying the different properties the substances had and grouping them together.

His work was relatively closely followed by that of a Russian scientist named Dmitri Mendeleev.

Dmitri Mendeleev arranged the elements by their atomic weight in the same way that Newlands did.

However, making him slightly unpopular, he decided that some of the atomic weights had been calculated wrong by his fellow scientists and figured that he could move those around in order to maintain groups of elements with similar properties together.

To then add insult to injury, he left gaps within his table for elements that he believed had been undiscovered, suggesting that his fellow scientists needed to do more work.

Whilst having been ridiculed quite significantly during his life for his table, it turns out that once it had been published, many of the elements that he'd left gaps for were later discovered.

In fact, some of the elements were even discovered after his death and so his true genius wasn't recognised until long after he had created his table.

The undiscovered elements are shown here within his table by hyphens.

You can also see that he has the groups across the top and the beginning of what looked like periods down the side of the table.

It was quite some time then, before anybody else took the periodic table and began to make changes.

It was in 1913 a scientist called Henry Moseley was working as part of a scientific group who discovered the proton.

In doing so, he was able to reorder Mendeleev's table and instead of using the atomic weight, he started to use the atomic number, the number of protons found within the nucleus of each of the elements.

This led to the modern periodic table as we know it today, with the eight groups as we can see identified across the top, and the six periods.

By having this slightly stepped appearance, showing it stepping down between Group 2 and the transition metals and then up again before reaching Group 3, allowed elements with similar properties to still be kept together.

The periodic table hasn't changed much since Moseley's time, aside from the addition of Group 0.

Time for a quick knowledge check.

Which scientist proposed the Law of Octaves? Was it A Newlands, B Mendeleev, or C Moseley? Octaves refers to eight and it was John Newlands who spotted that every eighth element showed similar properties.

Which two of these scientists ordered their tables based on the atomic weight? A Newlands, B Mendeleev, or C Moseley.

The correct answer is A Newlands and B Mendeleev.

Both of these two scientists used atomic weight, whereas Moseley used the atomic number.

Which scientist left gaps in their table for the undiscovered elements? Was it A Newlands, B Mendeleev or C Moseley? The correct answer is B Mendeleev, although he wasn't thought of favourably for doing so.

And finally, which scientist discovered the proton which helped to create the modern periodic table? A Newlands, B Mendeleev or C Moseley? The correct answer is C Moseley.

Well done if you've managed to get all of those right.

Now it's time for a practise task.

In task A, we'd like you to match the scientists to their periodic table ideas and in B, starting with the earliest, number the scientists to show the order in which they contributed to the development of the periodic table.

I'd recommend that you pause the video now and give this task your full attention and when you're ready to hear the answers, press play.

How did you find that? Hopefully not too tricky.

Let's see how you've done.

So Newlands should be matched with saw each eighth element had similar properties.

Mendeleev, quite cleverly, left gaps for undiscovered elements and Moseley ordered the elements by their atomic number.

We then asked you to start with the earliest, number the scientists to show the order in which they contributed to the development of the periodic table.

It was John Newlands who first spotted that each eighth element had similar properties and so he should be numbered one.

This was then followed up by Dmitri Mendeleev and then finally, after the discovery of the proton, the periodic table was reordered by Moseley.

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

If not, you can always go back and watch this section of the video again and have another go.

So we've taken a look at what are properties and how the early periodic table was largely ordered using them.

Now it's time to have a look at the modern periodic table and compare it to some of the earlier versions.

So the modern periodic table arranges their elements of who said by the atomic number.

Remember, this is the number of protons that we find in the nucleus of each of the atoms. The metals are on the left of the periodic table and the non-metals on the right, as you can see here.

On the left hand side of the line, going from aluminium stepping down, those are all metals.

You can see there are considerably more metals in the periodic table than there are non-metals.

The columns are numbered as Groups from one to seven and then Group 0 on the end.

Each of the rows is now what we refer to as a period and gives us additional information about the structure of the atoms that we find in those rows.

It's quite common to be asked to compare Mendeleev's periodic table with that of the modern version.

If we take a look at the two, we can see that there are some significant similarities.

We can see that there are groups in both the modern and Mendeleev's table and that there are clearly rows.

We can identify that some of the elements are occurring in the same places, although there are also some important differences and that's what we're going to try to spot now.

One of the first major differences is that Mendeleev's table was arranged by the atomic mass, whereas the modern period table is arranged by atomic number.

Mendeleev couldn't possibly have used atomic number because the proton hadn't been discovered when he put his table together.

Mendeleev's table left gaps.

Although this made him unpopular with fellow scientists, it actually turned out to be a work of genius as later, those elements were discovered and placed in and so in our modern periodic table, there are now no longer gaps.

Mendeleev's table, due to the lack of discovery of some elements, had only 63 elements, whereas our modern periodic table as close to 118.

And then lastly, you may notice if you look closely, that Mendeleev's table has no Group 0, whereas this does exist on the modern periodic table today.

This is because Group 0 are known as the noble gases.

This group of gases are what's called inert and unreactive.

They were the last elements to be discovered because they are so unreactive, they weren't happened upon by accident during experiments by scientists and so were added much later as a group on the end, on their own.

Let's do a quick knowledge check there and see what you can recall.

True or false? Mendeleev's periodic table is exactly the same as the modern periodic table.

Being as we've just had a little go at spot the difference, I'm going to say that this is false.

Mendeleev's table was arranged by the atomic weight, whereas our current periodic table is arranged by atomic number.

So, over to you for a practise task.

The first part of this task asks you to place a tick in the correct boxes to show if the description applies to either Mendeleev's periodic table or the modern periodic table.

You'll want to pause video now so that you can take some time to consider your answers and when you're ready to hear the correct responses, press play.

How did you do? Great, I'm sure.

Let's take a look and see if your answers match up with mine.

So the first description says it's arranged by atomic number.

The atomic number is the number of protons and so must refer to the modern periodic table.

The Group 0 elements being missing is a feature of Mendeleev's periodic table.

Gaps were present for the undiscovered elements and so this must also be Mendeleev's table, as all elements we now believe to have been discovered and placed within the gaps that were left and finally arranged by atomic weight.

Well, the modern periodic table as we've already said, was arranged by atomic number, so arranged by atomic weight must be a feature of Mendeleev's table.

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

Let's take a look at task B.

Task B asks you to complete the sentences by filling in the gaps.

This will give you a nice summary paragraph about the development of the periodic table.

You'll need to take a little bit of time to consider your responses, so we suggest you pause the video now and press play when you're ready to go through the answers.

Let's take a look at how you got on.

It was John Newlands who proposed the Law of Octaves as he spotted that every eighth element had similar properties.

Dmitri Mendeleev helped to create the modern periodic table by leaving gaps for the undiscovered elements.

Both Newlands and Mendeleev ordered the elements by their atomic weight.

The modern periodic table is arranged by the atomic number and it has columns, that we call groups, and rows, that we refer to as periods.

Well done if you got those right.

On to our third and final task.

Whose table of elements improved on Newlands' and how? There's three marks available for this question, so we need to be very clear in answering it.

We need to identify which scientist improved on Newlands' table and how that was an improvement.

You'll want to pause the video and take a few moments to consider your response, making sure that you explain your answer clearly, highlighting how the table was improved upon.

When you're ready to hear the answers, press play.

How have you done? Right, so three parts.

We must be able to achieve at least one mark for saying who the scientist that followed Newlands was, Mendeleev.

So if you've written Mendeleev you've achieved one of the marks available out of the three.

We then need to go on to explain how his table improved.

Well, he left gaps for the undiscovered elements.

What this meant was that the elements with similar properties were kept in the same groups and so led to the development of the groups that we see today within the modern periodic table.

Really well done.

That was a tricky one.

So if you've managed to get marks on this question, you're doing really well.

We've reached the end of our lesson today.

So let's take a look at some of our key learning points.

Properties are the chemical and physical characteristics of substances.

The three major contributors to the periodic table were Newlands, Mendeleev and Moseley.

The layout of the periodic table has changed as we've learnt more about the properties and particles that make up the elements.

And the modern periodic table is arranged by the atomic number.

This is the number of protons.

It has columns called groups and rows called periods.

I hope you've enjoyed our lesson today as much as I have.

I'd like to suggest that you have a go at the exit quiz before you sign out today.

Thank you for choosing to use Oak National Academy and we hope to see you again soon.

Bye for now.