Video: Periodic Table development

﻿Hi, my name is Dr. Patel and welcome to the 11th lesson in this topic of atomic structure and periodic table. In today's lesson we're going to be learning all about the developments in the periodic table. Before we start today's lesson I'd like you to do a couple of things for me. Firstly, can you make sure that you're sitting in a nice quiet space, and you haven't got any distractions around you. So if that means that you need to close down any unwanted computer tabs, or move your mobile phone away from you if you're not using it to access today's lesson, do so now. Great. Next, I want you to write today's date and title at the top of your page, and today's title is the development of the periodic table. So in today's lesson you're going to need all of the equipment that's listed on the screen. You're especially going to need a copy of the periodic table. So make sure that you've downloaded it from the downloadable resource section if you haven't already done so. So this is the periodic table that you should have in front of you. Throughout today's lesson, I'd like you to try and make some notes on it if you've managed to print it out, but don't worry if you haven't managed to print it out you can just make notes of the key bits of information within your notes. And in today's lesson, we're going to start off by looking at the main features of the modern periodic table. Then, we're going to go into the history of the periodic table, because believe it or not, it didn't always look the way that it does today. So let's start off with the modern periodic table. So as you probably already know, the modern periodic table is a list of all the known elements that we know exist. And there are 118 different elements that have been discovered. Now all of these elements are organised in a very specific way. They haven't just been randomly placed into the positions that they're in. You will notice that the periodic table contains columns, and rows. Now you might remember that the columns are called groups, and that they link very specifically to the structure of the atom. Do you remember from a previous lesson, how the group number links to electrons? Well done if you remembered that the number of electrons in the outer shell, is also the number in the group. So for example, all group one elements contain one electron in their outer shell, all group three elements contain three electrons in their outer shell, and all groups seven elements contain seven electrons in their outer shell. Now you may notice that there is also a group zero, they're actually referred to as the noble gases and they actually have a full outer shell, and we'll be learning about that next lesson. But the main thing that you need to know is that the columns are called groups. Another feature of the periodic table is these quite distinct rows. Again, these are not randomly arranged, they are called periods, and they refer to the number of electron shells that occur within that atom. So for example, if an element is in period one, it will have one shell, if it's in period two, it will have two shells, and so on and so forth. So the rows are called periods and they represent what? Well done if you're paying attention, it is the shells. So the periods represent the number of shells, and the groups represent what? The number of electrons in the outer shell. Another main feature, is the fact that the elements are ordered in order of their atomic number. So if you look at the smaller number for each element, you will see that each number goes up by one as you go across the periodic table. So for example, lithium has got an atomic number of three, and then its neighbour, beryllium, has got an atomic number of four. So the modern periodic table is actually arranged in order of atomic number. So let's see how many of those facts you remember. What are the rows called on your periodic table? Excellent, they're called periods. Complete the sentence: The modern periodic table is arranged in terms of... Well done if you remembered atomic number. What are the columns called on the periodic table? So the ones that go down, what are they called? Good, they're called groups. What does the group number represent? Do you remember? Excellent. They represents the number of outer shell electrons. What does the period number represent? Well remembered, it's the number of shells. Okay, for the next set of questions, if you feel like you need some more time to find the elements on the periodic table, pause the video and try to find it. So what group is sodium in? Good, it's in group one. Okay, so we know what group sodium is in, what period is sodium in? Excellent, it's in period three. Okay, so, just to make sure that you've understood the very basics about the modern periodic table, pause the video now and answer these questions and then resume playing the video once you've answered these. So here's what you should have got: The rows on the periodic table are called periods. The columns are called groups. And the group number actually represents the number of electrons on the outer shell. And here's the answers to questions four and five. Make sure you've corrected it if you need to do so, but well done if he got them all right. Okay, so looking at the modern periodic table, we know that we've got groups, we know that we've got periods, and we know it's arranged in terms of atomic number. What else can we learn about the periodic table? So we can actually identify where the metals and non-metals are found on the periodic table by using this zigzag line. So if you need to add this to your copy of the periodic table, please do that now. Do you know what this represents? Good, one side represents the metals and the other side represents the non-metals. Okay, so on the left hand side of that zigzag line, we have all the metal elements, and on the right hand side of that zigzag line, we've got all the non-metal elements. So you can see that there are way more metal elements than they are non-metal elements. Make sure you know how to find the metals and the non-metals in this periodic table, as it's especially important when we learn about bonding later on. Okay, so let's see how much you remember. On which side of the periodic table are non-metals found? Excellent, is the right hand side. There's way fewer non-metals than there are metals. On which side of the periodic table are metals found? Brilliant, they're found on the left hand side. Is calcium, a metal or a non-metal? You might want to pause the video now so that you can find calcium on your periodic table, and work out which side of the periodic table it's in. Excellent, it's a metal So actually if you found calcium, it's in group two, and therefore it's on the left hand side of the periodic table, and therefore it is a metal. Okay, so is helium, a metal or a non-metal? This time I've highlighted helium for you in a pink box. So is it a metal or non-metal? Well done if you said it's a non-metal. Is actually found on the right hand side of that zigzag line and therefore it belongs to the non-metal family of elements. Is lithium, a metal or a non-metal? Good, it's a metal. Is calcium, a metal or a non-metal? Excellent, it's a metal. Is boron, a metal or a non-metal? Good, it's a non-metal. It's actually on the right hand side of that zigzag line, and therefore, it's considered to be a nonmetal. Okay, so now it's time for some independent practise. Pause the video now and answer these three questions. For question three, the first example element has been done for you. So just use sodium as your worked example. So here's what you should have got. Pause the video now and compare your answers with the ones provided, resume playing the video once you've done this. So believe it or not, the periodic table hasn't always looked like it does today. It's taken the work of several scientists to actually build to the version that we have today. I'm just going to talk you through a couple of scientists that have contributed towards the current day periodic table. Now one of the earliest periodic tables that was developed, was developed by the scientist John Newlands, and this is what his version of the periodic table look like. He arranged the elements according to atomic weight and he noticed, that every eighth element had very similar reactions. So this was known as the Law of Octaves. Now, it's really important that you understand that at that moment in time in the mid 1800s, subatomic particles hadn't been discovered. And so he couldn't possibly have organised the elements in order of atomic number or atomic mass, he had to organise them based on their atomic weight. Now, one of the fundamental problems with the way that he organised his elements, was that sometimes you would get elements in the same group that had very different properties. So for example, fluorine, which is a non-metal, was in the same group as sodium and magnesium. And similarly, you also got chlorine, potassium, and calcium grouped together. So to summarise, Newlands arrange the elements in his periodic table according to atomic weight, not atomic mass or atomic number, and the key problems with Newland's periodic table were that sometimes you got elements with different properties within the same group, and that led to sometimes metals and non-metals being grouped together. Pause the video now if you need to take any notes on Newland's periodic table, resume playing the video once you've done this. So the next scientist I'm going to introduce you to is Dmitri Mendeleev. Now he was a Russian scientist that is known as the godfather of the periodic table. Like John Newlands, he ordered his elements according to atomic weight, not atomic mass, not atomic number, but atomic weight. He also noticed that elements with similar properties needed to go in the same group. And so he also ordered the elements according to their properties. However, he noticed that in order for him to be able to only have elements with similar properties in the same group, he actually needed to leave spaces in his periodic table. And he predicted that those elements were undiscovered yet and that they will be discovered at a later date. More importantly, because of the way that he grouped the elements according to the similar properties, he could actually predict the properties of those undiscovered elements. So for example, he actually correctly predicted the properties of the element gallium, decades before it was even discovered. Pause the video now and make sure that you've got any notes that you need on Mendeleev's contribution to the periodic table. So true or false: John Newland's periodic table had metals and non-metals in the same groups. Good, it's true. So his version of the periodic table, because he didn't leave any gaps he had sometimes metals and non-metals in the same group. So in the early periodic table, the elements were ordered according to what? Well done if you got atomic weight. If you said atomic number, it's the modern periodic table that is organised in terms of atomic number. And since subatomic particles hadn't been discovered yet, the elements couldn't be ordered in order of atomic mass. What two factors did Mendeleev use to order his periodic table? Excellent, it's atomic weight and their chemical and physical properties. True or false: Mendeleev correctly predicted the properties of undiscovered elements? Absolutely, I think it's phenomenal that he was able to accurately predict the melting and boiling points of elements that he didn't even know existed yet. True or false: Mendeleev's periodic table didn't have groups. That's false. There were clearly groups on his periodic table, and those elements had similar properties. Okay, so now I want to see whether you can compare the modern periodic table with Mendeleev's version of the periodic table. And to do this, you're going to start off by completing a Venn diagram. Now some of you will already be familiar with Venn diagrams, and others of you may never have used one before. So what you've got to do is you've got to take the statements in the pink boxes, and you've got to place them into the correct section of the Venn diagram, which is the two overlapping circles. So I'm going to do one as a worked example. So let's take the second statement. Ordered elements using atomic weight. Now was that Mendeleev's periodic table, in which case it would go on the left hand side? Was it the modern periodic table, in which case it would go on the right hand side? Or was it both of the periodic tables, in which case it would go in the overlapping ring? So well done if you said that it was in Mendeleev's periodic table, and so you would have placed it on the left hand side. So now what you need to do is you need to take the rest of the statements and place them into the right section. Pause the video now and have a go. If you can think of any of your own ideas about what's similar and different, then please do add them to your own Venn diagram. Okay, so here's what I got. So in Mendeleev's periodic table, the elements were ordered according to atomic weight, and it contained lots and lots of gaps. By comparison, the modern periodic table is ordered according to atomic number, and it contains every element. And then, there's some features that are present in both Mendeleev's periodic table and the modern periodic table, and that's that both periodic tables contained groups and both sets of groups had similar properties. You may have also come up with some of your own, and that's fantastic that you're actually thinking independently. Okay, so let's take everything you've learned and apply it to an exam style question. So for this question, you need to compare the similarities and differences between the modern periodic table and Mendeleev's periodic table. So whenever you're writing an answer to a compare question, you need to make sure that you're using comparative language. So for example, within a sentence you will say whereas, or however, or in comparison to. In order to make your answer really successful, you need to make sure that you've used all of the key words that are listed in the support box. Pause the video now and have a go at writing down your answer with as many similarities and differences as you can think of. You might want to use the Venn diagram to support you, and then resume playing the video once you've done this. So, these are the kinds of things that you should have written down: In pink, we've got the similarities, and in turquoise, we've got the differences. Pause the video now and make sure that you've got these key points written down and add to your answer if you need to. So that brings us to the end of today's lesson. Hopefully you have a better understanding of what today's modern periodic table looks like, and the main features, and you have a better understanding of how the periodic table has developed over time. Before you finish today's lesson, please make sure you go and complete the quiz. It's a really good way of checking your understanding and celebrating all your hard work in today's lesson.

Worksheet: Periodic Table development

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In this lesson, we will describe the main features of the modern periodic table, describe early versions of the periodic table, and then compare the modern periodic table with the early periodic tables.

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