In Our Time - Chemical Elements

Episode Date: May 25, 2000

Melvyn Bragg and guests discuss the chemical elements. The aim and challenge in chemistry, according to the Encyclopaedia Britannica, is the understanding of the complex materials which constitute everything in existence since the Big Bang, when the whole universe emerged out of the two elements of hydrogen and helium. For Aristotle there were four elements: Earth, Air, Fire and Water. Now there are one hundred and eight, sixteen of which are produced artificially, and none of which figure in Aristotle's original four. But they are all still elements - defined as substances which cannot be broken down, the building blocks of all life.Today we have the key to understanding these elements, the Periodic Table, which is a pattern embedded in nature and was miraculously discovered in a dream. With Paul Strathern, former lecturer in philosophy and science, Kingston University and author of Mendeleyev's Dream: The Quest for the Elements; Dr Mary Archer, Visiting Professor of Chemistry at Imperial College, London; John Murrell, Emeritus Professor of Chemistry, University of Sussex.

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Hello, Aristotle thought there were four elements, earth, air, fire and water. He was wrong. There are

110 so far, 16 of which are produced artificially, and none of which figure in Aristotle's original four, but they're all still elements, defined as substances which cannot be broken down, the building blocks of all life. Today we have the key to the understanding of these elements, the periodic table of the elements,

which is a pattern embedded in nature and was, as it were, miraculously discovered in a dream. With me to discuss chemistry's continuing mission to understand the behaviour in the relationship of these irreducible substances, he's Dr. Mary Archer, visiting Professor of Chemistry at Imperial College London, John Mural, Emeritus Professor of Chemistry at Cessack University,

and Paul Strathen, author of Mendeleev's Dream, The Quest for the Element. Paul Strathen, why did Aristotle choose Earth, Air, Fire and Water, and why did you think that these were the four elements? He arrived at this, well, he wasn't the first person to think of these four as a combination. It was Empedocles who did that. He took the idea on from Empedocles, who had the four. the notion of the four.

At one stage, a very lovely poetic image, he describes how a stone falls into a pool. He thought that the four elements, the heaviest ones at the bottom, Earth, then you had water, then you had air, and then you had fire. And he describes his evidence as being when a stone drops into a pool,

it drops to the bottom of the water, and the bubbles adhering to it are then drawn towards their own element, and they go up through the water towards the air. Also, when you light a fire, the fire always goes upwards. This was his idea. The four elements had their four places,

and his evidence for them as such would have been something like that image. And the qualities that he saw in substances, earthiness, wateriness, fariness, and so forth. Mayor Yarchab, why did such, what turned out to be such a completely erroneous idea. Why did it hold a sway over science for almost 2,000 years? Well, it is, I think, quite a fruitful idea because earth, air and water are the three states

of matter, solid, liquid, and gaseous. And as Paul said, those are qualities, if you like, and they're observable qualities. And fire, if you like, heat or energy is something that provides things with their warmth and ability to move and flow. So the idea erroneous, though it now seems, was far from unfruitful, except insofar as if you believe that all the different solids like gold and lead and stone were in fact made of one set of qualities, it was quite rational to believe you could term one into the other. so you could turn base metals into gold by somehow adjusting the relative amounts of fire and earth

and water that they contained. And to that extent, I suppose one could say that the old classical idea led into alchemy, which was itself not fruitless, all the great operations of chemistry, the basic operations, distillation, fractionation, crystallization, all the rest of it. They were the developments of the alchemists.

Chemistry goes way, way back. After all, the entire stuff of the world and indeed of the universe is made of chemical entities. And transforming one to another and learning how to control that, the art of chemistry, goes way, way back beyond ideas of atoms and elements. But I suppose by saying there were only four elements, or only two or three as later people came to think. That was starting people off on too narrow a path

because, as you said, at the last count, there are 110. And that was a thought that required a lot of a big leap of the imagination to say there are more elements here. John Morrow, let's get back to Aristotle for a moment. I didn't believe I said that. Anyway, never mind. No, no, I want to say something about Aristotle. So you do want to say something about Aristotle, I think.

I certainly do, yeah. Well, shall ask you a question? Or you just... I'll just carry on. I mean, you know, I don't have much time for Aristotle. He held back physics for 2,000 years. But on one thing, it's quite surprising. He actually defined an element,

and that definition almost holds up today. An element is something to which other bodies can be resolved and which exists in the ether, potentially or actually, but which cannot itself be resolved into anything simpler. Now, you could almost write that in a textbook. So that's an extraordinary thing. No, we're not talking about four elements.

We're talking about, as you say, 110 principle. Nevertheless, Aristotle got that one right. But it's extraordinary, I think, notwithstanding what Mary Archer says, there were 13 elements known to the ancients, things like gold, etc. And there was this 2,000 years almost of attempting to churn one into the other with dismal failure, although spin-off, because by doing those experiments,

they actually did discover things. But it took a surprising long time for that pattern to be extended so that you were actually talking around the beginning of the 19th century in terms of elements as we now know them and discovering. these things and in discovering by the 1800 or so one had I suppose something like 30 elements available

and being able to build on those. Can I come back finally to this question that I've asked the other two as well, why do you think briefly that this idea which turned out to have advantages as Mary Archer's pointed out and attractions as Paul has pointed out

but it was wrong. Why did it hold sway for such a long time when a lot of work as being done in the Arabic world on mathematics and so on and on chemistry there. And yet this holds very strongly. Well, there was a very strong... And you think to bad effect. You don't like that, that's right. Well, I'm sure it held things back enormously, but there was a very strong emphasis on pattern. Of course, the elements themselves had symbols in terms of geometrical solids like octahed and tetrahed and things like that.

But if you look at the history of developing knowledge in Western Europe, the starting of significant university systems in the 13th century. As far as science goes, what they had essentially were books of Aristotle. I mean, that was what was worked on. And this is what people worked on for the next 500 years. It's an extraordinary manner. And with attacks from the church, of course, during that time. But people who called themselves scientists were Aristotelian scientists in those days.

I think that's right. You've put your finger on it, that the works of the ancients acquired a sort of biblical status as authorities, and one thing scientists shouldn't do is defer to historical authority. They should be skeptical. Yes, that the Royal Society has as its motto and took us its motto when it was coming into the scientific age, not by authority. In other words, they weren't going to accept anything unless it was proved and seen experimentally. But earlier stuff on those things we were saying before about Aristotle, a lot of this was supported by beliefs. For instance, a lot of the miners believed that metals matured in the ground that lead gradually grew into silver and gradually grew into gold. John Morrow, do you think he was the Anglo-Irish scientist Robert Boyle

who finally, as it were, knocked down Aristotle or at people like How do you be challenged by earlier philosophers and scientists? Well, there'd been plenty of challenges, and of course there'd been, to some extent, attacks from the church on Aristotle's works. And Boyle himself tried to put the definition of the element into more vigorous terms. A relatively modest change, in my view.

But he certainly did. I mean, Boyle certainly came out very strongly against the Earth. Yes, the skeptical. chemist, I think that was a seminal work. It said, why do we believe there are only four elements when we know, in fact, there's copper, tear, arsenic, all the rest of it? Why should we not believe there are more elements? But his definition wasn't, in fact, very much different from Aristotle's.

The anything was that because the chemists were unable to, in fact, his working definition was anything that you can't spit any further, and because they didn't have the techniques to do it, and a lot of several substances which were thought to be elements turned out to be compounds. And again, I think the reason why chemistry was held back, apart from the Aristotelian idea, was when the scientific revolution came,

it was Galileo's revolution, it was a revolution of measurement, a revolution of where physics became joined to mathematics. You measured how long something was, how heavy something was, or placed where it was. And it's notoriously difficult, especially with the substances, the apparatus they had at their disposal, to measure colours and smells

and changes of that sort and gases. Indeed, and the whole point about chemistry is you can make things into other things, and so it's very, very difficult to sort out what you actually can't decompose into something simpler. Can I come back to John Marl here, about Robert Boyle. about the skeptical chemist.

I'm trying to find out some sort of progression. We get to boil. Is the fact that he makes his experiments open? Is that a big factor in it that we have somebody saying, this is what I do, this is how I do, this is, I incurring. Is that a factor? Well, science. Science was both open and closed.

I'm amazed at the amount of secrecy that still was, the fact that people like Newton wrote some of his results of his experiments in code because he wanted the credit, but he didn't want other people to know what he was doing. But there was a lot of publication was very important throughout Europe in those times, and books were being written. I think the advance of chemistry is, as Paul was saying, the onset of proper measurements,

Boyle did certainly very important ones. Lavoisier is really the key to this, who started to measure in fine detail how chemical compounds were being formed from different things, and that this conservation of matter is really something that we put Lavoisier essentially 1800. We're talking about the late 18th century. Absolutely.

That's when chemistry starts, and it starts, I think, as a branch of physics, almost, the people who are doing it to some extent were physicists as well as. Well, the priestly as well in this country, and in France you have La Boisier and there's an argument as who invented water with logistics and becoming oxygen and so.

But that, as far as your concern, is when the chemistry, as it were, chemistry starts in front of you. LaVosite is known, especially in France, as the father of chemistry. Yes. I think he has the credit, probably. But he wrote the most important first textbook. So can you just briefly say

why this is such an important starting point from modern chemistry for you? Well, there were two important steps. First of all, in distinguishing what we call a compound and what we call a mixture. And that these compounds had very definite weights and mixtures of elements in them, and in Britain we had the absolutely crucial developments of Dalton, John Dalton,

who gave us the formulae, gave us the recipe at any rate, for understanding how these different elements combined in definite proportion. So that was seminal development all at the same time. Cumbrian Dalton. If you were going to be a chemist, I think you'd have to be a chemist between sort of 1790 and 18, 20. And Lavoisier threw out the phlogiston idea, which was an extraordinary throwback to the fire. element of Aristotle.

Phlogiston was the theory of Becker and Stahl. It was a sort of principle of heat. He also did one thing, I think, which is terribly important and often overlooked, is that he systemised the names. He called oxygen. He called phlogiston oxygen. Yes, he called phlogiston. He called hydrogen.

He named hydrogen, hydrogen, from the Greek hydra-idra-water, gen-generator. and he gave all the chemical, as many substances as he could, names that became standardised throughout the scientific world because previously they'd had lots of different names, old housewives names, medical names, different names and different countries, Latin names. He formalised it and he also formalised the number pattern. So we have the elements and we have at the heart of the elements

a serious puzzle and problem, which, and we skip, just let's skip, 60 years to 1869 when the subject of your book, although you go through the entire history, Mendeleev, who found the key when he discovered the periodic table of the elements. Can you tell us why it was important to find the key and how he did it? It was important because so many elements, again, were being found, much like the idea of Lavoisier. There seemed to be all these elements,

and there seemed to be that people began to discover certain patterns of behaviour. and Doberina, a German chemist, came up with the idea that they happened in threes. Newlands came up with the idea the law of octaves, that there were patterns of eight elements with recurring properties. This wasn't liked, actually, at the time, because science had turned away from theory and was relying very heavily on experiments. And so when people started theorising about,

the elements. This wasn't taken very well. In fact, Newlands, when he presented his idea of the law of the octaves to the Royal Society, at the end of his speech, one of the older members stood up at the back and said, well, perhaps next week you can come back and give us a list of the elements in their alphabetical order. And that will tell us what they're all about. But to go on to Mandelaev, Mendelief's table was important. a German called Maya came through with a very similar table at the same time

but why Mendeleu was important was because he discovered a pattern, he discovered gaps in that pattern, there were certain gaps in it, and he forecast that these would be filled by elements, he forecast too what properties and what weights these elements had, so this was a structure that covered everything. He also, very boldly said where certain elements didn't fit in, He said they've got the weight wrong

and they better go away and try again to get the... And he turned out to be right. And also the two gaps, Eka silicon and Echre aluminium, he predicted would be there and they were found. Yes. And the way he found it, which we haven't got time to go into the environment, is graphically described. We know a lot about that those particularly two or three days.

He worked himself in the ground, exhausted him, trying to catch all those sort of things. Fell asleep, had a dream, worked up with period tables. actually the sort of thing that's described by Poincaray as the way in which jumps in his area science are made, and a lot of people in different areas know about this sort of unconscious working. But Mary Archer, can you tell us about the periodic table, which was, as it were, the discovery side of invention? What's useful about it and what is it, how is, can you tell us how it is a blueprint? Well, it is the sort of central idea of chemistry.

It's a sort of railway timetable with rows and columns, and it arranges all the chemical elements from the lightest, hydrogen and helium, through to the heaviest, uranium and plutonium and beyond, in order essentially of increasing atomic weight. Really a thing called atomic number, which I'll come on to. But the atomic weight is determined by how many protons and neutrons there are in the heavy nucleus of an atom. All atoms have got a heavy nucleus, which is positively charged,

and around that circle electrons, which are negatively charged, and the whole atom is electrically neutral. And the lightest element, hydrogen, just has one proton with one electron circling around it. Then the next one, helium, has two protons, with two electrons circling around it, but also in the nucleus two neutrons, which gives it a mass, roughly speaking, of four, compared with hydrogen. So what Mendeleev did, and in his dream and with his ideas of games of patients, he was laying them out in such a way that he could see the patterns,

the suits, if you like, of chemistry. And he laid them out so that they were in order of ascending atomic weight. They knew nothing about atomic numbers and nuclei in those days. that waited another 50 years or so and wrote them out in sort of rows which chemists call periods under each other so that these elements with similar chemical properties would appear underneath each other

so for example group 7b the halogens chlorine bromine iodine or reactive rather nasty gases group 8b I think it is the coinine metals, copper, silver, gold, they appear underneath each other. But then along in the rows, in the periods, this is the really clever bit, and I think this is mental airs brilliance,

they don't all have equal numbers. The first row just has two elements, hydrogen and helium. Then the next row has eight elements. And then the next row has eight elements. There are the two short periods. Then the next two rows have 18 elements. And then the next one, one beyond, that has 32. And the ingredients of much of that are in Mendeleu's classification, and that was really brilliant because those magic numbers, 2, 8, 8, 18, 18, 32 require quantum mechanics to explain them because they're to do with the shells in which the electrons live around the nucleus.

And the first shell can only hold two electrons, and it's hydrogen and helium. the next shell holds eight and so on and so forth. Thank you. John Murrell, can you explain to us how great a breakthrough of this force for chemistry? It has been compared with Newton, with gravity in physics and Darwin's evolution in biology. Is that overreaching or is it in that area? I don't think it's overreaching. What I'd first like to emphasise is that this periodic classification

simplifies the teaching of chemistry. That's a terribly important thing. for students to know that when no longer has to teach separately the chemistry of 92 elements but you actually teach them in families and some of that came on quite lately in

I mean even when I started doing chemistry it wasn't as emphasised as clearly as that but it certainly emphasised now that one talks about patterns the other thing from the research point of view it meant that if you knew a molecule that was made

up, say, of one atom in group eight and three atoms in group three, then you'd be able perhaps to predict that there might be a whole family of molecules of that type, which would exist, which would only change the type of element, group eight element you're doing, the type of group three element that you were talking about, and you would be able to obtain, for example, sulfur dioxide and selenium dioxide and tullium dioxide, and tullium dioxide, before these things were actually made, you would be able to predict

what experiments are going to be useful to do, certainly in inorganic chemistry. What the Newtonian gravity in physics did was to enable things to happen, which had not happened before, because with that knowledge, people went on. Ditto with Darwin's evolution. What has gone on?

What has moved on because of this classification, because of these periodic tables, and the consequences of that. Well, chemistry has become a less random mixing of bottles. That's a gross abuse of chemistry anyhow, but after that time, the predictions of what you might be able to do were certainly much clearer.

But what is it enabled, is what I'd like to know. I mean, did it... Didn't enable new molecules to be made? Yes, but did it lead on to us? Without that table, could we not have had... Would we not have led on to DNA, for instance? Well, I doubt very much whether DNA comes into it because generally speaking, the periodic table had a huge influence within what we call inorganic chemistry, which is the bulk of the elements, whereas organic chemistry, which is predominantly connected with carbon, is another family, and a restricted set of rules apply.

One would have got organic chemistry, I think, even if the periodic table hadn't been there. But inorganic wouldn't have been in existence. would have been a hopeless map. Ultimately, the periodic table is a classification. It's like the linean classification. It's not a discovery in itself. It's a way of writing down the chemical elements that summarises and is consistent

with all the more fundamental properties of those elements. And as you say, John, it tells you what will combine with what and in what proportions, the whole idea of valency, as chemists call it. It showed them in those days. There were gaps where they, Jollywell ought to be able to discover elements

and it was a great sensation I think when gallium which was ecker aluminium was discovered and germanium which was eke silicon that was you know it was like discovering uranus I think it validated the idea so it did have predictive force

to Einstein's idea of when he predicted that the rays would bend for the sun and when this was backed up years later by Eddington making an observation to the eclipse I think the discovery of gallium and germanium were exactly those you know he predicted something and they have been fulfilled

well i'm just going to say it is important to know that mendeleve knew about 63 elements at the time by the end of the century there was something like 1992 those have now been extended further but it was a marvelous achievement to actually get the periodic classification out of 63 of the 92 no it's a cleverest thing was to leave the Yes. Do you think it's too frivolous to suggest maybe this is his creation of new elements through particle collisions is in some way

validating alchemism? Absolutely. It is the only way you turn one atom into another is to get at its nucleus and make it fuse like in the sun hydrogen fuses to form helium

and then beyond in a supernova explosion or to smash them apart by hurling neutrons at them you can turn one atom into another. So maybe if we actually could understand and read and get hold of Newton's notebooks and alchemy, maybe he's all there. Maybe he invented the first nuclear reactor then.

I was probably Leonardo da Vinci, Melbourne. But that might have been, obviously, this is happening, and they in their furnaces were trying to do, what must have been trying to do this, wasn't it? Yes, I've got a lot more sympathy with the alchemist than I think Paul has. Chemists spend their life making one thing into another, and it's entirely logical, I think, at that stage to think you could have made one element, as we now call it, into another.

They had no reason to suppose there was some indivisibility about copper, tin, arsenic, except that they could never break them down into two simpler substances. And it was that idea that slowly came through that the chemical element is the building block, the simplest entity in the chemical world. It took a long time to surface. Where do you think that the edge of chemistry is now, John Morrow? What do you think it's... Well, I think the edge of chemistry is the borders that it has primarily with the other sciences. I'm quite sure that chemistry and biology

are going to revolutionise medicine. In what works? 30 years or... Biological chemistry. I'm totally. It's the golden age of biological chemistry. And the second thing is materials because I'm sure chemistry and physics is going to revolutionize materials

with nanostructures, being considered at the present time, which is another subject, but that's very important. So we go into a chemistry laboratory now, you see a lot of things going on in the centre. New molecules, difficult to get at molecules, are still being made with surprisingly marvellous techniques, but also the edges. And what has linked with what? And supramolecular assemblies, molecules that are so clever that they slot together in locks and keys, like enzymes and antibodies, as it were.

And I think in the course of time, chemists will be so smart. They will be able to synthesize live entities, things that are so smart that they replicate. We have not yet synthesized life. I think we will. I think it's going to be possible in some near future to create life in an artificial womb?

Not in the near future, but... In the medium-term future, I think it's certainly possible. People are beginning to synthesize green leaves, if you like, in test tubes, and they've got as far as something that will fix ADP to ATP, that's the principle of muscular power. I'm sure we will get far enough to create molecules or molecular assemblies that replicate themselves and therefore are alive. Well, thank you all three of you very much indeed.

That's Paul Strath and Dr. Mary Archer and John Morrow. I'm back next week to talk about the American Ideal with Susan Sondarkritavichens and John Keane. Thanks for listening. We hope you've enjoyed this Radio 4 podcast. You can find hundreds of other programmes about history, science and philosophy at BBC.com.com.com.com.com.