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Atoms and the Periodic Table
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About the lecture
In this mini-lecture, with a look at the periodic table and it’s elements, as well as various models of the atom. As we move through this mini-lecture we discuss: (i) the Plum Pudding Model and the Nuclear Model of the atom, where through the Geiger and Marsden experiment we see that the Nuclear Model is the accurate model; (ii) the nucleus of an atom, which is made up of protons and neutrons; (iii) how the periodic table is organised and labeled; (iv) the importance of nucleons in keeping the nucleus intact through the nuclear force; (v) nuclear binding energy; and (vi) finally, nuclear fission and fusion.
About the lecturer
David Berman is a Professor of Theoretical Physics at Queen Mary. His research interests include string theory and ideas in fundamental theoretical physics, including non-commutative geometry, black holes physics, and quantum gravity. He has contributed to the Radio 4 biography series Great Lives and the In Our Time podcasts, including Great Lives: Richard Feynman (2018), Great Lives: Galileo (2019), In Our Time: Emmy Noether (2019), and In Our Time: Paul Dirac (2020).
Hello.
00:00:06I'm Professor David Berman
00:00:08from Queen Mary University of London,
00:00:09and I'm going to talk to you
00:00:12about the building blocks of the universe.
00:00:14What are the building blocks?
00:00:16What makes up this incredibly complex universe around us?
00:00:18And also,
00:00:22how do we discover what these building blocks are?
00:00:23So it's a complex world with many different things that make up a whole load of
00:00:27different materials that surround us the air that you breathe the wood of a table,
00:00:32the metal that conducts electrons through wires that drive your computer.
00:00:37These are all very different things.
00:00:43And yet
00:00:45we have the question.
00:00:46How many fundamental building blocks do we need
00:00:48to make all of this things up together?
00:00:51Well,
00:00:55what's the answer to that?
00:00:56Is dependent upon how small you want to look.
00:00:58How small should your fundamental building blocks? B.
00:01:02The idea goes all the way back to the Greeks,
00:01:06who had this notion that there were elementary
00:01:08things that built up everything around them.
00:01:11For the Greeks,
00:01:15this was just some simple notions of earth, wind, fire and water.
00:01:16But modern science
00:01:20found a way of determining what these building blocks really were.
00:01:22So
00:01:26first,
00:01:27let's look at the periodic table.
00:01:28The periodic table
00:01:31is
00:01:33a table which organises together
00:01:34different so called elements,
00:01:37and the elements distinguish themselves
00:01:39by having different chemical properties.
00:01:42They would react with each other in different ways,
00:01:44and
00:01:47each one of these would have a different mass.
00:01:48So
00:01:52what people discovered
00:01:53is that you could organise all these different elements together
00:01:54into periods and groups
00:01:58where
00:02:00various elements would share similar chemical properties.
00:02:01And also there was a very clear way in
00:02:06which elements will get more heavier and heavier.
00:02:09As you went up the table.
00:02:12One question remained, though,
00:02:15which is
00:02:17why this table, why this structure
00:02:19was there something deeper that made up these different elements
00:02:23with their different chemical properties
00:02:27That could explain
00:02:29the structure of the periodic table.
00:02:31To understand
00:02:35what makes the different elements in the periodic table different,
00:02:36we have to understand
00:02:40the idea of the atom.
00:02:42J. J. Thompson
00:02:44discovered
00:02:46that an atom
00:02:47was made up
00:02:49of both positive
00:02:50and electrically charged objects,
00:02:52so in fact,
00:02:54those elements
00:02:56were not elementary at all,
00:02:57but made up
00:02:59of a combination
00:03:00of positive and negative charges.
00:03:02What followed next
00:03:06was an attempt to understand how
00:03:07those positive and negative charges organised themselves
00:03:10inside each one of those elements.
00:03:14The first thing is,
00:03:18let's give some things names,
00:03:19Thompson
00:03:22called the negatively charged particle. He discovered
00:03:23the electron,
00:03:26and then we had
00:03:28some positive charges,
00:03:30and we'll come to what are called later.
00:03:31There were two different ideas
00:03:35about what made up the atom
00:03:37about how those positive and negative charges
00:03:39were distributed.
00:03:42One of them, called the plum Pudding model um,
00:03:43plum pudding is more popular Back then,
00:03:47was that the electric and positive charges were just evenly distributed,
00:03:49much like plums inside of pudding
00:03:55or
00:03:58something which became known as the nuclear model
00:03:59that where you'd have
00:04:02a central nucleus,
00:04:03much like a son
00:04:05with the negatively charged objects orbiting around it like the planet
00:04:06that was called the nuclear model.
00:04:11And with these two competing ideas,
00:04:14it came down to experiment, to work out how you could tell them apart.
00:04:17This experiment
00:04:22was done in Manchester
00:04:23by Geiger and Marsden,
00:04:25and what they did
00:04:27was to take gold leaf,
00:04:29which they could make super incredibly thin,
00:04:31so that it was basically one atom thick
00:04:34and then
00:04:38scatter
00:04:39a particle off it called alpha particle
00:04:40and then, through its scattering,
00:04:43work out whether the plum pudding model
00:04:46or the nuclear model
00:04:49was the reflection of reality.
00:04:52Was it
00:04:54the positive charges
00:04:55in the middle? And then they give charges on the outside?
00:04:57Or were the charges just evenly spread?
00:05:00You can see from this diagram
00:05:06that when we look at when we scatter things
00:05:08from an atom,
00:05:11we can see
00:05:12that they scatter very differently, depending on the model
00:05:14in the plum pudding model. Because everything is evenly distributed,
00:05:17then the charges sort of go through
00:05:21and slightly deflect.
00:05:24But
00:05:26if we have the positive charge is
00:05:27centralised in the middle,
00:05:29then when those other positive charged particles scatter,
00:05:31if it hits that middle bit, then they scattered very strongly.
00:05:37If it doesn't hit the middle bit, they don't scatter at all.
00:05:41That gives a very different scattering process
00:05:44that was measured
00:05:48and people determined.
00:05:49It was, in fact,
00:05:50the nuclear model of the atom
00:05:52that were so familiar with now
00:05:54of a nucleus in the middle that's positively charged
00:05:56and negatively charged electrons orbiting it.
00:05:59That was the atom,
00:06:03and we saw that we had this nucleus,
00:06:05this positively charged object in the middle.
00:06:07But that nucleus
00:06:11is itself made up
00:06:12of two sorts of elementary particle,
00:06:14the proton,
00:06:17which is positively charged
00:06:18and in fact
00:06:20its charge is equal and opposite
00:06:22of that. The electron
00:06:24and the neutron,
00:06:26which is neutral,
00:06:28carries no charge.
00:06:29Both the proton
00:06:32and the neutron
00:06:33are much heavily in the electron.
00:06:34In fact, one proton
00:06:37is almost 2000 times
00:06:38the mass of an electron,
00:06:40so most of the mass
00:06:42of our atoms
00:06:44comes from the nucleus.
00:06:45Now
00:06:47let's go back to the periodic table
00:06:48and see
00:06:51if knowing something about atomic structure
00:06:52can tell us about how those elements are organised.
00:06:55First of all,
00:07:00all the atoms
00:07:01are neutrally charged,
00:07:02which means
00:07:04there is the same number of protons and electrons.
00:07:05The electrons
00:07:09will organise, how things chemically bind and combined
00:07:11and determine the reactive properties of the element.
00:07:15So because the number of protons
00:07:19is the same as the number of electrons,
00:07:21in fact,
00:07:24the periodic table's organised by the number of protons
00:07:25that are live in the nucleus,
00:07:30which is called the atomic number.
00:07:32Hydrogen has one proton in the middle.
00:07:35Iron has 56 protons in the middle.
00:07:38But let's not forget the neutrons,
00:07:41the neutrons will actually make up almost half of the mass
00:07:44of the atom.
00:07:48But in fact,
00:07:50a given atom can have a different number of neutrons.
00:07:51And that's what different isotopes are
00:07:55different isotopes
00:07:58as something
00:07:59with the same number of protons
00:08:00but different numbers of neutrons.
00:08:02Let's look at our periodic table
00:08:06and let's just look at some of the notation
00:08:08that we have.
00:08:10So the letter
00:08:12is the name of the element
00:08:13and then
00:08:15the superscript.
00:08:16In this example, 12 for carbon is the number of protons and neutrons added together
00:08:18and then six. The subscript is the atomic number,
00:08:24the number of protons.
00:08:27And as you can see,
00:08:30the periodic table goes up in atomic number.
00:08:31And then you can look at the mass
00:08:36and then you'll see
00:08:39that those masses
00:08:40is roughly the average mass is found in
00:08:41nature of the different isotopes of that element.
00:08:44Why are the neutrons there?
00:08:47What do they do?
00:08:50The protons, which are all in the nucleus,
00:08:52have the same charge.
00:08:54They would electro magnetically repel each other.
00:08:57What holds them there?
00:09:01If you just rely on the electromagnetic force,
00:09:03they certainly shouldn't be able to stay together,
00:09:05What the neutrons do
00:09:09is that they bind
00:09:11with the protons
00:09:12and each other
00:09:14using what is known
00:09:16as the nuclear force.
00:09:17The nuclear force
00:09:20is thousands of times stronger than the electromagnetic force,
00:09:22but actually only acts on very short distances
00:09:26roughly the scale of the nucleus.
00:09:30Which is why we've never seen it
00:09:32outside of a nucleus.
00:09:33So what they do
00:09:36the neutrons
00:09:38is there needed in an atom
00:09:39to bind together the protons
00:09:41and overcome the electromagnetic repulsion
00:09:43and keep the nuclear stable?
00:09:46If you only have a few neutrons,
00:09:49the strong nuclear force
00:09:51isn't big enough
00:09:52to keep the protons together.
00:09:54We always need
00:09:56enough neutrons
00:09:57to keep
00:09:59the atom stable.
00:10:00What people do
00:10:02is plot
00:10:04the binding energy
00:10:06of the nucleus,
00:10:07and here we have a plot.
00:10:10What it tells us
00:10:13is that given
00:10:15a number of nuclear arms in the nucleus,
00:10:18that means the neutrons and protons together
00:10:20how much binding energy there is.
00:10:23The more binding energy,
00:10:26the more strongly bound the nucleus is,
00:10:28the less binding energy.
00:10:31Well,
00:10:33the less
00:10:33and it's got this very peculiar shape.
00:10:36It goes up very, very sharply
00:10:39from hydrogen
00:10:41and then curves around
00:10:43until it reaches iron
00:10:45and then starts to go down again
00:10:47until you go all the way up
00:10:50to uranium
00:10:52and the radioactive elements,
00:10:54which are actually further down than the more stable iron.
00:10:56With the nuclear binding energy curve,
00:11:01we can describe why and how we get energy
00:11:03from nuclear fission,
00:11:08a nuclear fusion
00:11:09by the splitting
00:11:11or bringing together
00:11:13atoms.
00:11:14Let's first look at nuclear fission,
00:11:16where we break apart and nucleus.
00:11:18Let's look on the curve
00:11:22that uranium 235.
00:11:24When we break it apart, we will climb the curve.
00:11:25And that difference
00:11:29between where we have 235 nucleons or something like 120
00:11:31well, give us a difference in energy
00:11:37and that binding energy
00:11:40then gets released
00:11:42as
00:11:43energy through radiation and heat.
00:11:44That's the thing which powers nuclear reactors, makes nuclear bombs.
00:11:47We also have
00:11:51another way.
00:11:53If we go all the way down to hydrogen
00:11:54and then go
00:11:58up
00:11:59along the curve
00:12:00to hire elements like helium,
00:12:02then what we'll see is that again
00:12:05we get a release of binding energy,
00:12:08and that binding energy
00:12:12is what powers the sun.
00:12:14The amazing thing is, from this curve,
00:12:17you can see why fusion is so much more powerful than fishing.
00:12:19When we went from uranium all the way down
00:12:23to some lower elements,
00:12:27we gain quite a bit of binding energy.
00:12:29But just that huge jump
00:12:31from the binding energy of hydrogen to helium
00:12:33is enormous.
00:12:36And that's why many people believe
00:12:38fusion is the future
00:12:40for power.
00:12:42So far,
00:12:44we've seen
00:12:45that all of the material world
00:12:47is built
00:12:49from simple building blocks,
00:12:50the elements
00:12:52and then
00:12:54inside the elements,
00:12:55explaining the periodic table,
00:12:56the atoms
00:12:59and the atoms, protons,
00:13:00neutrons
00:13:02and electrons.
00:13:03We've learned
00:13:05what makes them up, how they're organised.
00:13:06And then
00:13:09what binds the nucleus
00:13:10of the atom together? What binds the protons and neutrons
00:13:13and finally,
00:13:17that there's a binding curve of energy
00:13:18and that gives rise to fission
00:13:21and fusion.
00:13:23Now we're going to learn
00:13:26and see
00:13:28if there's anything more
00:13:30than protons, neutrons and electrons.
00:13:31After all, they make up so much the world around us.
00:13:33But what more have we found?
00:13:37
Cite this Lecture
APA style
Berman, D. (2022, January 12). Topic 3: The Standard Model - Atoms and the Periodic Table [Video]. MASSOLIT. https://massolit.io/options/topic-3-the-standard-model?auth=0&lesson=4422&option=16879&type=lesson
MLA style
Berman, D. "Topic 3: The Standard Model – Atoms and the Periodic Table." MASSOLIT, uploaded by MASSOLIT, 12 Jan 2022, https://massolit.io/options/topic-3-the-standard-model?auth=0&lesson=4422&option=16879&type=lesson