Speaker 1: Even before we could pry open molecules and see the
Speaker 1: structure of atoms, we knew there was something fascinating going on.
Speaker 1: There had to be some kind of internal structure there.
Speaker 1: Why did we think so? How did we know? Well,
Speaker 1: because the periodic table is periodic. There are groups of
Speaker 1: atoms with similar behavior. As you march across column by column,
Speaker 1: atoms in those same columns have similar behaviors conductivity, reactivity.
Speaker 1: That can't just be random, and of course it isn't.
Speaker 1: It's because of the structure inside each atom, which was
Speaker 1: long invisible to us. The structure of the atom is
Speaker 1: of course dictated by quantum mechanics, which also reveals something
Speaker 1: about the basic laws of the universe. And now electron
Speaker 1: structure is the source of torture for high school chemistry
Speaker 1: students and physics podcast hosts, but it also completely and
Speaker 1: totally diff finds our world. It's why metals exist, why
Speaker 1: things are hard or soft, or liquid or solid. It's
Speaker 1: not magic, but changes to these properties can have dramatic
Speaker 1: effects on elements behavior, and the nature of our experience.
Speaker 1: And today we're going to dig deep into what might
Speaker 1: be the weirdest element on the periodic table. One that
Speaker 1: isn't just sensitive to quantum mechanics, but to our other
Speaker 1: great theory of physics relativity. Mercury, and here I mean
Speaker 1: the element, not the planet, whose orbit was famously predicted
Speaker 1: by relativity. Is very strange because it's liquid at room temperature.
Speaker 1: It's the only metal we know that is liquid at
Speaker 1: room temperature that you can pour without ever heating it up.
Speaker 1: It's even liquid if you put it on ice or snow.
Speaker 1: This is knowledge we share with the ancients. The name
Speaker 1: mercury comes from its Greek name, which I won't try
Speaker 1: to pronounce, but means watery silver. Why what is so
Speaker 1: special about mercury? What is going on inside that? Adam?
Speaker 1: Welcome to Daniel and Kelly's extraordinarily chemical universe.
Speaker 2: Hello. I'm Kelly Wienersmith. I studied parasites and space, and
Speaker 2: because I was a child of the nineties and we
Speaker 2: got ourselves into all sorts of trouble, I had a
Speaker 2: necklace that was a vial of mercury. Oh no, And
Speaker 2: now I'm just glad it never got like smashed on
Speaker 2: me or something.
Speaker 1: Are you sure it wasn't permeable in some way?
Speaker 2: It would explain a lot.
Speaker 1: Folks, Kelly would be so much smarter if it wasn't
Speaker 1: for that necklace. Oh oh ouch, I mean she's already
Speaker 1: super smart. I don't think we could handle it even
Speaker 1: smarter Kelly.
Speaker 2: Oh good cover. I love it.
Speaker 1: Well. I'm Daniel. I'm a particle physicist, and I'm not
Speaker 1: a big fan of chemistry, but I am in awe
Speaker 1: of its influence over our world.
Speaker 2: Yeah. I was surprised to see that you picked a
Speaker 2: chemistry tim. Then you did this to us on purpose,
Speaker 2: and so let's try to focus on positives for chemistry
Speaker 2: for like half a second. What was your favorite moment
Speaker 2: in a chemistry class?
Speaker 1: Ooh, I remember taking the final and being done with it.
Speaker 2: Amazing.
Speaker 3: No.
Speaker 1: I was recently talking to the daughter of a friend
Speaker 1: of mine and asking her what she wanted to study
Speaker 1: in college, and she said chemistry and I said cool. Why?
Speaker 1: And she said, chemistry is very tactile. It relates to
Speaker 1: things that are right in front of us. It controls
Speaker 1: how things operate. It's almost like you can do magic.
Speaker 1: And she was right, you know, like, particle physics is
Speaker 1: very cool and reveals the fundamental nature of reality blah
Speaker 1: blah blah. But it talks about things you can't see really,
Speaker 1: and so like, how do you know the electrons are
Speaker 1: following those rules or the quirks are doing this or that,
Speaker 1: whereas like you can see stuff flow or boil or
Speaker 1: bond or reflect or whatever. It really does determine the
Speaker 1: nature of our experience.
Speaker 2: Yeah, I agree, and I disagree. I agree on like
Speaker 2: a global level. So I did my senior honors research
Speaker 2: work in an organic chemistry lab because even though I
Speaker 2: talk about how much I disliked chemistry, I had a
Speaker 2: lot of chemistry friends and I was kind of into
Speaker 2: it for a while.
Speaker 1: But didn't know that about you, Kelly. Hmmm, oh my god,
Speaker 1: recalibrating over here.
Speaker 2: I made so many mistakes in the chem lab, though
Speaker 2: I'm so lucky I didn't die. But you know, I
Speaker 2: would mix things together and I'd be like, all right,
Speaker 2: clear liquid mixed with clear liquid, and it still looks
Speaker 2: like a clear liquid. Did I do the reaction I
Speaker 2: was trying to do? I don't know. And so I
Speaker 2: know there's a lot of stuff where it's like you
Speaker 2: can see stuff's happening, but there's also a lot of
Speaker 2: stuff where you have to just like expect the thing
Speaker 2: happening you thought was going to happen, and it's yeah,
Speaker 2: I don't know. I like fish. You can really see
Speaker 2: what's going on with fish.
Speaker 1: You can see fish guts, but you can't see atomic guts.
Speaker 1: That's the issue, that's.
Speaker 2: Right, that's what you can't see the backside attack happening
Speaker 2: in real time. I think that was a chemistry reaction
Speaker 2: that my friends and I maybe focus done a little
Speaker 2: bit too much. But anyway, we had some fun.
Speaker 1: Yeah. Well, you know, underlying chemistry is physics, and there's
Speaker 1: a close relationship between chemistry and like quantum physics. It
Speaker 1: determines the nature of the atoms. And what we're going
Speaker 1: to discover today is that the answer to the question
Speaker 1: of the episode might not actually be chemistry, it might
Speaker 1: be physics.
Speaker 2: After all all that, I think we just found our
Speaker 2: video uplip for this episode. You have the right voice
Speaker 2: for an evil scientist.
Speaker 1: Left. Wow, I'll put that in my next grand proposal.
Speaker 2: Okay, so today we're talking about why mercury is liquid
Speaker 2: at room temperature. And I didn't know the answer to
Speaker 2: this before reading the outline, and you know, to be honest,
Speaker 2: since it's a brief outline, I still don't think I
Speaker 2: know what the answer is, but I will by the
Speaker 2: end of the hour. And so let's see what our
Speaker 2: audience thinks about why mercury is liquid at room temperature.
Speaker 1: So think about it for a moment yourself. Do you
Speaker 1: know the answer? Is it chemistry? Is it is it
Speaker 1: some weird combination? Is it physical chemistry. Here's what our
Speaker 1: audience had to.
Speaker 3: Say, just characteristics of that particular.
Speaker 1: Element based off of the chemistry of the items. So
Speaker 1: this sounds like a will make for a very interesting episode.
Speaker 3: Mercury may not be very good at sharing its electrons
Speaker 3: and that's why it is a liquid at room temperature.
Speaker 4: I think it's because the amount of energy that's required
Speaker 4: to break the bonds to turn into a liquid is
Speaker 4: really low, because it's just a bit quake. And yeah,
Speaker 4: like my son, I think it's because of dragons as.
Speaker 5: Well, something to do with its electron orbitals.
Speaker 6: I guess that the heavier the element, the more solid
Speaker 6: it should be. But mercury is a have metal, so
Speaker 6: this might not be an adequate explanation. Maybe this is
Speaker 6: related on how the molecules mercury utforms because of.
Speaker 3: The way it's electrons behave Actually it has to do
Speaker 3: with the way that they are bonding or in this
Speaker 3: case not bonding, so it's a very weak chemical interaction.
Speaker 1: Maybe it has something to do with how the electrons
Speaker 1: were arranged.
Speaker 7: I thought mercury was a liquid at room temperature for
Speaker 7: a similar reason as to why water is as well,
Speaker 7: how the bonds between the atoms work and interact.
Speaker 4: Mercury is liquid at room temperature because it's solid at
Speaker 4: a different temperature, a lower temperature.
Speaker 1: I don't really know why metals are liquid at any temperature.
Speaker 2: I don't know now I'm curious.
Speaker 5: It's valence electrons are paired, which I guess makes it
Speaker 5: less necessary for it to form the kind of crystal
Speaker 5: structure that you get in most metals, because it's outermost
Speaker 5: electron shell loses electrons easily and does not form strong bonds.
Speaker 3: Has to do with the specific heat of the substance.
Speaker 1: I knew, aw forgot.
Speaker 6: That at room temperature, the chemical bonding between the atoms
Speaker 6: are weaker than in cold, where they get stronger.
Speaker 2: I love the answer that they would love to know this.
Speaker 2: There are so many amazing patterns in the periodic table.
Speaker 2: I love that curiosity about chemistry. You and I should
Speaker 2: maybe try to channel that a little bit more.
Speaker 1: I totally agree with that answer. I think it is
Speaker 1: amazing the patterns in the periodic table, and I love
Speaker 1: how it reveals the structure of the universe, and it
Speaker 1: is very very cool. It's just also very complicated. Wow,
Speaker 1: it's not easy. So you know, my fear of chemistry
Speaker 1: is mostly in awe of the people who can do it,
Speaker 1: because I can't.
Speaker 2: I found it very difficult. Mostly I was spilling the
Speaker 2: chemicals on myself or dropping the glassware. But my favorite
Speaker 2: moment in chemistry actually was the very first college chemistry
Speaker 2: class I took, where we got the melting point and
Speaker 2: some other features of some unknown substance, and by calculating
Speaker 2: these different features of the unknown substance, we were able
Speaker 2: to figure out what we had been given. And that
Speaker 2: felt like amazing, like forensic science CSI sort of stuff,
Speaker 2: and I just loved that. So I have a soft
Speaker 2: spot in my heart for calculating melting points, which is
Speaker 2: maybe not something I imagined i'd be saying when I
Speaker 2: was a kid, but I've never been cool, so I'm
Speaker 2: leaning in. So, Daniel, what determines melting points?
Speaker 1: M hmmm, Yeah, this is very cool. You know that
Speaker 1: we even have melting points for stuff, that things have phases.
Speaker 1: I think phases are super fascinating. You can have like
Speaker 1: the same set of atoms and a slightly different temperature.
Speaker 1: They're dramatically different behavior, right. This is not like a
Speaker 1: smooth transition where it's like kand of mushy and then
Speaker 1: kind of gassy. It goes from like solid to flowy.
Speaker 1: You know, it's really incredible that phases even exist. And
Speaker 1: I just want to nerrod out about phases for another
Speaker 1: minute before we dive in, because phases are a much
Speaker 1: more general concept in science and in physics than just
Speaker 1: like the state of matter. We use phases to describe
Speaker 1: any time there are a set of equations that have
Speaker 1: limited applicability, Like you could talk about Newton's equations for
Speaker 1: the motion of stuff applied to a certain phase of
Speaker 1: matter when things are not very massive and not very fast.
Speaker 1: It's like the Newton phase of mechanics. So I think
Speaker 1: it's really a fascinating concept because it admits that all
Speaker 1: our laws are limited, the way that like the laws
Speaker 1: of fluid mechanics only apply to fluids and the laws
Speaker 1: of crystal lattices only apply to crystals and not to everything.
Speaker 1: So anyway, I think that's sort of deep and philosophical.
Speaker 2: I think I'm not following all of the things that
Speaker 2: you just said. Still sound like you're talking about phases.
Speaker 2: So you said something about like how fast something's moving,
Speaker 2: and to me that makes me think about, you know,
Speaker 2: the transition from a liquid to a gas or something like,
Speaker 2: I'm missing the point.
Speaker 1: No, you're right, and they're all linked to like the
Speaker 1: behavior of the stuff. But you know, think about like
Speaker 1: the very early universe. We think there was a time
Speaker 1: when things were so hot and so dense that even
Speaker 1: our laws of quantum field theory might not apply. So
Speaker 1: there's like a phase in the universe when quantum field
Speaker 1: theory applies, and there's a phase when it doesn't apply. Right,
Speaker 1: Because it's not like a fundamental theory of everything. It's
Speaker 1: an approximation that only works under some conditions. In the
Speaker 1: same way like the laws of the liquid phase of
Speaker 1: water only work when water is liquid, that don't work
Speaker 1: when water is solid or when water is a gas.
Speaker 1: All of our laws are approximate that way and only
Speaker 1: work in a certain phase.
Speaker 2: Okay, Right, So when I was in my goth phase.
Speaker 2: The only thing that works for me was black clothing exactly,
Speaker 2: and I get it. Phase is a more general word. Yeah, okay,
Speaker 2: move it on.
Speaker 1: So what's happening here? The listeners were right. Things melt
Speaker 1: when the bonds between them loosen. Right. So a solid
Speaker 1: often is a crystal you have, Like these pieces click
Speaker 1: together into a crystal lattice. Not everything ends up like
Speaker 1: a crystal, you know, glass for example, like a big
Speaker 1: disordered mess. But lots of things click together form a crystal.
Speaker 1: You can imagine, like the little lego pieces snap together
Speaker 1: and it's very solid. It acts like a big chunk, right.
Speaker 1: And that happens because there are bonds between them.
Speaker 3: Right.
Speaker 1: These things don't just click together physically. They're just physically
Speaker 1: sharing the space. They are connected to each other. They
Speaker 1: are bound together because of what their electrons are doing.
Speaker 1: So if you have strong bonds between stuff and the
Speaker 1: stuff doesn't have a lot of energy, you can't wiggle
Speaker 1: around a lot, then it clicks together to form a solid. Now,
Speaker 1: heat that stuff up, give it energy. Make those atoms
Speaker 1: wiggle and jiggle and zoom. If they have enough energy
Speaker 1: to overcome the power of those bonds, then they will
Speaker 1: break open. That crystal lattice and they will slide around,
Speaker 1: and that's how they become a liquid. That's what melting is.
Speaker 1: It's breaking down the crystal lattice so that the atoms
Speaker 1: are more loosely bound to each other. There's still connected,
Speaker 1: there's still some bonds there. It's not totally a gas.
Speaker 1: Gas is when you give up all connection to each
Speaker 1: other and they're all just a bunch of independent molecules
Speaker 1: or atoms, so liquid. When you break those strongest bonds
Speaker 1: and now you have very weak bonds, so the atoms
Speaker 1: can flow over each other.
Speaker 2: Is it just that like some percent of the bonds
Speaker 2: have broken, or that bonds of a certain type have broken,
Speaker 2: like all the hydrogen to oxygen bonds have broken, but
Speaker 2: the carbon hydrogen bonds haven't broken yet. Or does it
Speaker 2: depend on the molecule that you're talking about.
Speaker 1: It depends on the molecule, but it also depends on
Speaker 1: the type. And so for example, after the bonds are broken,
Speaker 1: there are still some bonds there, but they're weird, very
Speaker 1: soft intermolecular bonds. You know, you can have like a
Speaker 1: bond between this water molecule and that water molecule because
Speaker 1: of its polarity, like maybe they're overall neutral, but it's
Speaker 1: got a little bit more negative on this side and
Speaker 1: a little bit more positive on that side, and that
Speaker 1: can attract the neighboring atom, or they can organize themselves
Speaker 1: that way. It's sort of a loose bond, whereas when
Speaker 1: they're tightly bound, then they use a different kind of bonds.
Speaker 1: You know. The electrons can like literally be shared among
Speaker 1: them in some kind of lattices, like in metals, the
Speaker 1: electrons just flow freely, right, You can't even really say
Speaker 1: which atom they're connected to, They just like flow all
Speaker 1: around the whole thinking you have really complex energy level
Speaker 1: structures for those electrons because they're really just shared. It's
Speaker 1: that one really big atom or one super molecule.
Speaker 2: You know, you and I might both know more chemistry
Speaker 2: than we've been letting on secrets coming out today.
Speaker 1: That's solid state physics.
Speaker 2: Oh no, all right, I was getting worried there. Okay,
Speaker 2: So it.
Speaker 1: Really is about the strength of the bonds. If atoms
Speaker 1: are capable of making very strong bonds, then it requires
Speaker 1: more energy to break them, higher temperatures to break them,
Speaker 1: So stronger bonds between the atoms mean a higher melting point.
Speaker 1: If there are already very very loose bonds between the atoms,
Speaker 1: like the atoms don't like the bond at all, or
Speaker 1: they use none of the very strong categories of bonds,
Speaker 1: then the melting point is going to be lower because
Speaker 1: it doesn't take a lot of energy to release the atoms.
Speaker 1: So we're going to take several steps towards the understanding.
Speaker 1: The first one is melting point is determined by the
Speaker 1: strength of the bond. Stronger bonds higher melting point, weaker
Speaker 1: bonds lower melting point.
Speaker 2: Okay, I've got that general concept. Can you get give
Speaker 2: me a little bit more information about what makes for
Speaker 2: a strong bond.
Speaker 1: Yeah. So you basically you're asking like, well, what makes
Speaker 1: the bond stronger, what makes the bonds weaker? Why does
Speaker 1: it depend on the element? What determines that? And the
Speaker 1: answer there is the electron structure. The electrons are the
Speaker 1: things that do the bonding, and so the electron structure
Speaker 1: is what determines whether the bonds are strong or whether
Speaker 1: the bonds are weak. For example, one of the most
Speaker 1: important thing is have the electrons filled up their shells,
Speaker 1: Like the electrons form these shells around the atom, you know,
Speaker 1: there's the first energy level, the second energy level. If
Speaker 1: that outermost energy level is filled, then the electrons in
Speaker 1: the atom are pretty happy and they don't want to
Speaker 1: go anywhere. If, however, they're not filled, you have like
Speaker 1: four out of eight or seven out of eight, then
Speaker 1: that atom is happy to take another electron, or to
Speaker 1: share another electron with its friend. So together they have
Speaker 1: filled shells. So for example, if you have hydrogen, hydrogen
Speaker 1: can have two electrons in its outer shell, but it's
Speaker 1: only got one, so it likes to find another hydrogen.
Speaker 1: So together they have two. They can share those two
Speaker 1: in a bond. So those two electrons are shared between
Speaker 1: the two protons, and that thing is really bound together
Speaker 1: into H two. I know, it's very coozy. Actually, where
Speaker 1: do they hate each other? What if they're like, oh
Speaker 1: my god, this guy never does the dishes.
Speaker 2: Oh I get that. I get that. But they can't
Speaker 2: get away from each other. Well, you got to turn
Speaker 2: up the heat so that they can escape.
Speaker 1: Oh, melting is like chemical divorce. Wow, fascinating. We are
Speaker 1: liberating these abs. You've heard of women's liberation. Now we're
Speaker 1: doing proton liberation.
Speaker 2: I thought it was electron liberation.
Speaker 1: There you go, yeah, electronic hand proton Yeah.
Speaker 2: Oh okay, got it.
Speaker 1: Yeah. So there's a few things that affect whether these
Speaker 1: bonds are strong or not. One is are the shells filled, right,
Speaker 1: So do you have a complete outer shell it's like
Speaker 1: a set of armor, it's hard to penetrate. Or do
Speaker 1: you have an incomplete outer shell, in which case the
Speaker 1: atom likes to bond. And we're going to go through
Speaker 1: some examples later on. You'll see that these patterns emerge
Speaker 1: in the periodic table. The other is how closely is
Speaker 1: it holding on to those electrons, because the electrons can
Speaker 1: be like really far out and sort of a distant
Speaker 1: outer shell very weakly held, or they could be like
Speaker 1: really tightly held. If the atom is very very powerful,
Speaker 1: if it has like a lot of protons in it, it
Speaker 1: can really hold those electrons close. So that also determines it.
Speaker 1: So we sort of like two dimensions here to determine
Speaker 1: whether the bonds are strong or whether the bonds are weak,
Speaker 1: or is it filled shells is it not filled shells.
Speaker 1: So filled shells means harder to form bonds, not fieled
Speaker 1: means easier to form bonds. If the electrons are close,
Speaker 1: it's harder to form bonds with them because they're held
Speaker 1: tightly by their nucleus and the electrons are not close,
Speaker 1: it's easier to form bonds.
Speaker 2: This is reminding me of the fun conversation that we
Speaker 2: had in response to a listener question about why life
Speaker 2: tends to be carbon based instead of silicon based. Yeah,
Speaker 2: silicon not silicone. I always mix those two up in.
Speaker 1: Orange County, it's silicone mostly.
Speaker 2: Actually, Yeah, well I live in Virginia where anyway, we
Speaker 2: don't need to go there. And the answer ended up
Speaker 2: depending on a lot of these questions.
Speaker 1: Yeah, but you're putting your finger on a really important trend,
Speaker 1: which is that as you go across the periodic table,
Speaker 1: elements in the same column tend to have the same
Speaker 1: electron structure. Right, they have like one extra electron or two,
Speaker 1: or it's totally filled, or it's not right. So the
Speaker 1: rows in the periodic table reflect the energy levels, and
Speaker 1: then as you march along the columns, you have the
Speaker 1: same pattern of the electrons filling up. So you go
Speaker 1: from left to right in the periodic table, you're filling
Speaker 1: up that outer shell. And so, for example, the last
Speaker 1: column in the periodic table all have their last one
Speaker 1: all filled up because it's the last one, and so
Speaker 1: that whole column are folks with very filled shells. That's
Speaker 1: why they're called the noble gases. They don't like to
Speaker 1: interact with anybody, and that's why they're all on the
Speaker 1: same column because at the same electron structure, which is
Speaker 1: why they have the same kind of behavior. And like
Speaker 1: the first column, all are noble gases plus one, so
Speaker 1: they all have one extra electron, one only electron in
Speaker 1: its own last shell really dying to do something with
Speaker 1: its friends. And so that's why those are all very active.
Speaker 1: For example, they like to react and they interact. So
Speaker 1: the electron structure really determines all these properties and the
Speaker 1: periodicity of the table.
Speaker 2: Now, I remember sitting in chemistry in high school and
Speaker 2: being like, all right, I think maybe I have finally
Speaker 2: memorized how many electrons are supposed to be in each
Speaker 2: one of these shells, But why are their shells in
Speaker 2: the first place? Yeah, And I never got a satisfactory answer,
Speaker 2: And maybe that's why I never could love chemistry until
Speaker 2: this moment, Daniel, because I'm gonna ask you, can you
Speaker 2: tell me why are there even shells?
Speaker 1: And do they sell? Them by the seashore. Right. Yeah,
Speaker 1: So the answer is, of course, the underlying physics quantum mechanics. Like,
Speaker 1: let's start with a simple atom like hydrogen. Hydrogen has
Speaker 1: a proton and it has an electron. Where could that
Speaker 1: electron be. Well, quantum mechanics says, use the Shorting equation,
Speaker 1: And Shorting equation says, well, there's a bunch of solutions
Speaker 1: for where the electron can be, a bunch of places
Speaker 1: where everything is copasetic and the wave function is happy.
Speaker 1: But there's a ladder of solutions. It's not a continuous
Speaker 1: state of solutions. Like let's zoom out and take a
Speaker 1: classical example where we have intuition the orbit of a planet.
Speaker 1: Where can a planet orbit the Sun? Well, classical mechanics says,
Speaker 1: if you have a certain radius, you need to be
Speaker 1: moving at a certain velocity in order to have a
Speaker 1: stable orbit. Cool, But every radius has a velocity, Like
Speaker 1: you could orbit the Sun at literally any place. There's
Speaker 1: an infinite number of available radii. Once you pick a radius,
Speaker 1: you have to have the right velocity. You'll fall out
Speaker 1: of orbit or you'll zoom out of the Solar system.
Speaker 1: But you could pick any radius, any solution works around
Speaker 1: hydrogen that we like to think of these as like
Speaker 1: planetary orbits, and there's lots of misleading pop side diagrams
Speaker 1: that convince you. So these are not orbits, right, These
Speaker 1: are solutions to the shortening equation, and there's a ladder
Speaker 1: of solutions. There's a finite number that's like number one,
Speaker 1: number two, number three. The quantum mechanics dictates that. And
Speaker 1: an intuitive way to think about why there are a
Speaker 1: discrete number of solution is to think about how the
Speaker 1: wave function fits around the atom. It goes around the atom,
Speaker 1: it has to reinforce itself, so when you go around,
Speaker 1: you have to come back and basically be in the
Speaker 1: same part of the wave and so you can fit
Speaker 1: like one wave or two waves or three waves, but
Speaker 1: you have like three point seven waves, then it's going
Speaker 1: to interfere with itself and it's not going to be
Speaker 1: a stable solution. So you want a stable solution of
Speaker 1: the electron around the atom, you have to fit a
Speaker 1: certain number of wavelengths of the wave function around the atom.
Speaker 1: So that's why you have a discrete number. That's what
Speaker 1: causes the shells. And then it gets much more complicated
Speaker 1: if you have more protons and multiple electrons. I mean,
Speaker 1: you get all the way up to like mercury. It's
Speaker 1: a mess.
Speaker 2: So does it have to be waves because electrons aren't
Speaker 2: point particles, they're actually waves, and that's where the wave
Speaker 2: thing comes in.
Speaker 1: Yeah, exactly. You have the wave function, which is a
Speaker 1: complex value thing, and it is really the thing that
Speaker 1: tells you where the electron can be. And so when
Speaker 1: the electron is in its lowest state, you shouldn't think
Speaker 1: of it like, oh, it's orbiting at a certain radius.
Speaker 1: It's got a probability distribution and that's the minimal stable
Speaker 1: configuration for that state.
Speaker 2: Okay, all right, got it. Chemistry is awful. That's what
Speaker 2: I think.
Speaker 1: The other crucial piece of physics is that electrons have
Speaker 1: this weird behavior where you can't have two of them
Speaker 1: having the same state. They just will not share. You know.
Speaker 1: They're like grumpy siblings. You cannot put two of them
Speaker 1: in the same bed. You need to have different rooms
Speaker 1: or they need to have something different. So the first state,
Speaker 1: you can have two electrons because one can be spin
Speaker 1: up and one can be spinned down. The second layer
Speaker 1: has more energy, so they can wiggle in different ways.
Speaker 1: There's different patterns to have their energy is distributed, so
Speaker 1: there's more options there. But quantum mechanics tells us that
Speaker 1: we can only have one electron per unique energy level,
Speaker 1: and as the shells get bigger, there's more options for
Speaker 1: the electrons for ways to differentiate themselves, so you can
Speaker 1: have two in the first one, and then I don't
Speaker 1: even remember the numbers, and I'm not going to guess,
Speaker 1: but yeah, it gets very complicated. But there are quantum
Speaker 1: mechanical answers for why there are a certain number of
Speaker 1: electors allowed in each shell, as to do with the
Speaker 1: polyexclusion principle and the number of ways you can distribute
Speaker 1: the angular momentum solutions in each energy level.
Speaker 2: In my head, at some point the number of electrons
Speaker 2: in the shells as you added shells started being the same.
Speaker 2: But I took chemistry when I was gosh, that was
Speaker 2: over thirty years ago, now, so that's just a bad memory, right.
Speaker 2: It's the number of electrons in each shell gets progressively
Speaker 2: higher the farther you get from the center.
Speaker 1: Yeah, okay, all right, but the shells then start overlapping,
Speaker 1: and you know sometimes like the highest energy subshell from
Speaker 1: level four is actually higher energy than the lowest energy
Speaker 1: subshell from level five. So level five fills up before
Speaker 1: the last level four fills up, and the ordering starts
Speaker 1: to get really, really nasty, which is why electron configurations
Speaker 1: are hard.
Speaker 2: I'm feeling angry. Why is it like that? All right?
Speaker 2: All right, let's give ourselves a chance to release the anger,
Speaker 2: and when we get back from this commercial break, we'll
Speaker 2: take up another peek at the periodic table and look
Speaker 2: for patterns and melting points and we're back. Okay. So
Speaker 2: at the beginning of the show, we talked about where
Speaker 2: you find electrons, how they fill up the shells, and
Speaker 2: how that impacts bonds between atoms. Now we're going to
Speaker 2: take a look at the periodic table because we're really
Speaker 2: interested in melting points to try to figure out why
Speaker 2: mercury is weird. So let's look for patterns in the
Speaker 2: periodic table to see what we should expect mercury to
Speaker 2: be doing in terms of melting points.
Speaker 1: Yeah, and there's a lot of really interesting stuff to
Speaker 1: dig into here, and a lot of it can be
Speaker 1: explained by chemistry. But mercury sticks out like a sore thumb,
Speaker 1: and so we're going to walk you through a couple
Speaker 1: of the trends that explain what's happening in the periodic table,
Speaker 1: but they can't completely describe mercury, and they're not actually
Speaker 1: enough to make mercury liquid at room temperature. So there's
Speaker 1: a little bit of physics we're going to need at
Speaker 1: the end to give you that complete explanation.
Speaker 2: Chemistry is never enough.
Speaker 1: Chemistry is never enough. So let's keep in mind that
Speaker 1: we're thinking about the electron structure of these elements, whether
Speaker 1: or not for example, they have a filled shell. And
Speaker 1: so let's like walk across the middle of the periodic table.
Speaker 1: So you have sc which is scandium, right, and then
Speaker 1: the next one is titanium, and it goes all the
Speaker 1: way across the copper and then to zinc. And if
Speaker 1: you look at the melting points here, they start pretty high,
Speaker 1: like scandium melts at fifteen hundred celsius, and then they
Speaker 1: go down to zinc, which melts at only four hundred celsius.
Speaker 1: Now that's pretty hot. You don't want to get into
Speaker 1: like a hot tub of zinc. But it's a big difference.
Speaker 1: It's like more than a thousand degrees difference. Why does
Speaker 1: scandium melt at a really high temperature, and zinc melts
Speaker 1: at a really low temperature. Because zinc is the end
Speaker 1: of this chunk of the periodic table, it's completed as shell.
Speaker 1: So zinc has a complete shell, which means it's not
Speaker 1: as likely to bond. It's not as easy for it
Speaker 1: to bond, which is why it has a lower melting
Speaker 1: point than all of its friends next to it, Like
Speaker 1: copper right next door to zinc, has a melting point
Speaker 1: of more than one thousand degrees C, where zinc again
Speaker 1: is just four hundred. And you see the same behavior
Speaker 1: in the next row, silver, which is right next to cadmium.
Speaker 1: Cadmium is just under zinc. Silver has a melting point
Speaker 1: of about one thousand C and cadmium of about three hundred.
Speaker 1: So just this one step over you add one proton
Speaker 1: and one electron, melting point drops precipitously, and the reason
Speaker 1: is that you filled up this shell. Now, these atoms
Speaker 1: can form the same kind of strong bonds where they're
Speaker 1: sharing electrons with each other, and so it's much easier
Speaker 1: to break them apart. So that's why zinc and cadmium
Speaker 1: and mercury, which is also in this column have much
Speaker 1: lower melting points than their friends copper, silver, and gold,
Speaker 1: which are right next to them in the periodic table.
Speaker 2: They're more stable, and because they're more stable, it's easier
Speaker 2: to make them liquid.
Speaker 1: It's easier to make them liquid because their bonds are weaker.
Speaker 1: It's not about the stability. These aren't like radioactive elements.
Speaker 1: It's just like do they like to click together? And
Speaker 1: zinc and cadmium and mercury all have a completed last shell.
Speaker 1: It's the S two, the four S two, the five
Speaker 1: S two, or the six S two. They've completed that
Speaker 1: little subshell, and so it's harder for them to form
Speaker 1: bonds like copper and silver and gold. The ones next
Speaker 1: door to them are missing one electron relative to our
Speaker 1: friends zinc, cadmium, and mercury. So they'd like to fill
Speaker 1: in that last shell. And if they meet another atom
Speaker 1: of their type, like two silver come together, they can
Speaker 1: complete that last shell together, and so they can form
Speaker 1: this kind of strong bond by sharing electrons. It's harder
Speaker 1: to break them apart. Mercury can't do that, cadmium can't
Speaker 1: do that, Zinc can't do that, so they can form
Speaker 1: the same kind of strong bond between the atoms, and
Speaker 1: so it's easier to break them apart, which means means
Speaker 1: a lower melting point.
Speaker 2: Got it, okay, thank you.
Speaker 1: So now we're comparing these two columns, right, Column eleven
Speaker 1: has a higher melting point than column twelve zinc, cadmium,
Speaker 1: and mercury. But still, mercury looks weird. Like zinc and
Speaker 1: cadmium melt at three hundred four hundred seeds, it seems
Speaker 1: like a very respectable temperature for a metal. Mercury melts
Speaker 1: at negative thirty nine c like, mercury has a crazy
Speaker 1: low melting point. Right. To make mercury solid, you have
Speaker 1: to get it to negative thirty nine celsius. That's very
Speaker 1: very cold, right, and it's a huge jump. And if
Speaker 1: you're saying, all right, well, this column is all colder
Speaker 1: than the other one. Still within the column, zinc and
Speaker 1: cadmium have a higher melting point than mercury. So what
Speaker 1: makes mercury so much lower than zinc and cadmium. Well,
Speaker 1: there is a trend there that we would expect. As
Speaker 1: you go from top to bottom in the column, you're
Speaker 1: getting heavier and heavier nuclei, right, Like, mercury has more
Speaker 1: protons than cadmium, which is more protons than zinc. And
Speaker 1: that's the other effect we talked about. Mercury holds on
Speaker 1: to its electrons more tightly than cadmium or zinc because
Speaker 1: it has more protons. Say you're an electron floating around
Speaker 1: the atom, there are more protons pulling you in, binding
Speaker 1: you tightly to that atom if you're mercury than if
Speaker 1: your cadmium or if you're zinc. Does that make sense
Speaker 1: kind of?
Speaker 2: So if your mercury, though, you also have more electron shells,
Speaker 2: and so your outer shell, which would do the bonding,
Speaker 2: is farther away from your heavy nucleus. They're farther away.
Speaker 2: What does that do?
Speaker 1: Yes, exactly. And this is my frustration with chemistry is
Speaker 1: that you can often tell your cells these intuitive stories
Speaker 1: and then somebody can come along with another intuitive sounding
Speaker 1: story that also makes sense, and you're like, huh hmmm,
Speaker 1: I don't know which one it is is right, you know,
Speaker 1: And the answer is that it's complicated. But overall the
Speaker 1: fact that they have more protons wins, and so it
Speaker 1: pulls these things in and you know, the way to
Speaker 1: think about it is like, yeah, these things can all
Speaker 1: be neutral. You have an equal number of protons and electrons,
Speaker 1: and the electrons don't like to be on top of
Speaker 1: each other. But still, these protons are very powerful and
Speaker 1: pulling them in, and each electron is having basically just
Speaker 1: a relationship with the protons, not with the other electrons.
Speaker 1: It's not like the power those protons is shielded by
Speaker 1: the other electrons. Instead it's now pulled in by eighty protons. Right,
Speaker 1: So it's a very powerful force. I think that one wins.
Speaker 1: But hey, chemistry experts out there right in and tell
Speaker 1: me if we got that wrong.
Speaker 2: Okay, so mercury really wants to be a liquid, and
Speaker 2: we know that because it has a full shell and
Speaker 2: it's really big. But even knowing those two things, mercury
Speaker 2: wants to be a liquid at temperatures way lower than
Speaker 2: what we would have expected. So where do we go
Speaker 2: next to try to understand that.
Speaker 1: Yes, so we're at the limits of chemistry here. Chemistry
Speaker 1: tells us yes, mercury should be lower than gold, for example,
Speaker 1: in the same way zinc should be lower than copper,
Speaker 1: and it is, and chemistry tells yes, mercury should have
Speaker 1: a lower melting point than cadmium or zinc because there's
Speaker 1: a bigger atom and it holds these things in and
Speaker 1: that's all cool. But if you run the calculations and
Speaker 1: you take all that into account, chemistry predicts that mercury's
Speaker 1: melting point should be eighty two C, but the measured
Speaker 1: value is negative thirty nine. See more than one hundred differents.
Speaker 1: So like, yes, there are these trends that suggest mercury
Speaker 1: should have a low melting point, but they suggest it
Speaker 1: should still be solid at room temperature. To get mercury
Speaker 1: even lower, To get that melting point down below room
Speaker 1: temp and even down below zero C, you need to
Speaker 1: do something else. Chemistry is not enough to make mercury liquid.
Speaker 2: On chemistry, get better with your predictions. This isn't physics.
Speaker 1: So you might think, well, it is quantum mechanics wrong,
Speaker 1: because chemistry is determined by quantum mechanics. We just told
Speaker 1: you about all the shells and the shortening their equation
Speaker 1: and all this stuff, right, So is quantum mechanics wrong. Well,
Speaker 1: quantum mechanics by itself is not wrong, but it's not
Speaker 1: the whole story. Right. We know that quantum mechanics doesn't
Speaker 1: describe the entire universe. Because quant mechanics, for example, can
Speaker 1: describe gravity, or black holes or the beginning of the universe.
Speaker 1: We have another theory in physics that helps us explain
Speaker 1: what happens when things get really really fast or when
Speaker 1: things get really really massive. That's relativity. All the calculations
Speaker 1: we've been doing, all the explanations we've been giving are
Speaker 1: chemistry based on quantum mechanics that assumes that relativity is
Speaker 1: not a thing. If, for example, assumes that there's no
Speaker 1: limit to how fast things can go, or that there
Speaker 1: are no black holes, we're essentially ignoring relativity and doing
Speaker 1: pure quantum mechanical calculations. And most of the time that's fine.
Speaker 1: Relativity is not really relevant. We're not doing chemistry around
Speaker 1: a black hole. We're not doing chemistry near the speed
Speaker 1: of light. So it works. But you know, sometimes it doesn't.
Speaker 1: And that's what's happening here, is that we've been ignoring
Speaker 1: the relativistic effects on the electrons of mercury.
Speaker 2: And that's because everywhere there's mercury, there's actually a tiny
Speaker 2: black hole next to it. Is that right? No?
Speaker 1: No, okay, though, but you know where you can get
Speaker 1: your mercury at.
Speaker 2: The flea markets.
Speaker 1: No in HG. Wells grown.
Speaker 2: No that was great.
Speaker 1: No it was not great, but thank you anyway. Yeah, So,
Speaker 1: what's happening here is not that there's a black hole
Speaker 1: next to every bit of mercury, although I love the
Speaker 1: theory and if you heard it that maybe every electron
Speaker 1: actually is a black hole and could we tell anyway.
Speaker 1: I love to talk about that on the podcast another time.
Speaker 1: You know, what's happening here is that electrons are actually
Speaker 1: relativistic around mercury. Mercury is so powerful with this nucleus,
Speaker 1: those eighty protons have such a strong hold on the
Speaker 1: electron that the electron velocities start to approach the speed
Speaker 1: of light. They're not going at like ninety nine percent
Speaker 1: the speed of light, but whereas electrons around hydrogen go
Speaker 1: about one percent of the speed of light, electrons near
Speaker 1: mercury move almost sixty percent of the speed of light,
Speaker 1: which is close enough for these relativistic effects to start
Speaker 1: to matter.
Speaker 2: So that suggest to me then that everything with eighty
Speaker 2: protons are more should also have these relativistic effects. Is
Speaker 2: that true? From there on out, we need relativity to
Speaker 2: understand the melting points of atoms.
Speaker 1: Yes, absolutely. And there's another guy under mercury in the
Speaker 1: periodic table, copronicsium, which is a crazy synthetic chemical element,
Speaker 1: which means we need to make it. It's not like
Speaker 1: found naturally in the wild, and people suspect that the
Speaker 1: relativistic effects for copronicsium are even stronger than from mercury.
Speaker 1: Mercury is something that's all over the place, so it's
Speaker 1: well studied and easy to play with. But turns out
Speaker 1: doing these calculations, including the relativity in our calculations, is
Speaker 1: very hard, which is one reason why only a couple
Speaker 1: of years ago were people able to do this calculation
Speaker 1: and predict the relativistic corrections to the original quantum mechanical calculations.
Speaker 2: Say that again, this time in English.
Speaker 1: So you can go out and measure the melting point
Speaker 1: of mercury, right, you put it on the table, you
Speaker 1: heat it up, you see it melt, you cool it down,
Speaker 1: you see it solidify. That's the measure value. Then you
Speaker 1: can go and say, I'm going to predict what it
Speaker 1: should be based on my understanding of what's happening. And
Speaker 1: they can do calculations, and they do these calculations like
Speaker 1: we referenced earlier on number of eighty two c that
Speaker 1: comes from using quantum mechanics to predict the strength of
Speaker 1: these bonds and understanding like at what temperature those bonds
Speaker 1: would break. So you're using quantum mechanics to predict the
Speaker 1: bonds and from that you can get the temperature. So
Speaker 1: that's the predicted value of mercury. Now, if you go
Speaker 1: in you say, well, I'm going to tweak quantum mechanics
Speaker 1: because I'm going to do quantum mechanics not by itself.
Speaker 1: I'm going to include relativistic effects in my quantum mechanics.
Speaker 1: Then you're changing what's going on in your predicted mercury,
Speaker 1: which changes the prediction of the bonds, which changes your
Speaker 1: prediction for the melting point. And so when we see
Speaker 1: a difference between our prediction and our observation, we know
Speaker 1: something is wrong. So we go back and tweak our
Speaker 1: predictions to make it right. And you know, in principle
Speaker 1: we should always be using relativity to get everything right.
Speaker 1: But most of the time it's irrelevant. You want to
Speaker 1: calculate when the train is going to go from Cleveland
Speaker 1: to New York. Relativity doesn't have any impact, right, so
Speaker 1: you can ignore it. Also, relativity is a huge pain, like,
Speaker 1: it's non linear, it's complicated, it's not easy to do.
Speaker 1: So most of the time, if you can't ignore it,
Speaker 1: you should. But when you discover that your non relativistic
Speaker 1: calculations are not up to the task, when they're getting
Speaker 1: me answer wrong, that's when you've got to go back
Speaker 1: and do your homework and include the physics in your calculation,
Speaker 1: because it turns out it's necessary beautiful.
Speaker 2: Okay, all right, So now we've got electrons moving super
Speaker 2: fast and now we're incorporating relativity. What is the jump
Speaker 2: from there to understanding why melting point is affected?
Speaker 1: Yeah, so first we should clarify which part of relativity
Speaker 1: we're including, because folks, everythinking Daniel's been telling us that
Speaker 1: quantum mechanics and relativity can't play nice together, like that's
Speaker 1: the whole goal of modern physics has come up with
Speaker 1: quantum gravity and understanding the early universe and blah blah
Speaker 1: blah and string theory.
Speaker 2: That's right, Daniel has been telling us that.
Speaker 1: And that was not a load of baloney. That's all true.
Speaker 1: That refers to our fail to unify quantum mechanics with
Speaker 1: general relativity, the theory of gravity and curvature and all
Speaker 1: sorts of crazy stuff, which we have not been able
Speaker 1: to do. But we have, and it's been decades and
Speaker 1: decades since we've done this. Unified quantum mechanics and special relativity,
Speaker 1: the theory of what happens when things go near the
Speaker 1: speed of light and incorporates the fact that light is
Speaker 1: always the same for all observers and that nothing can
Speaker 1: go faster than light. Special relativity, which is just like
Speaker 1: flat space, but includes things like time dilation and length
Speaker 1: contraction and maximum speeds and weird velocities and stuff. That's
Speaker 1: special relativity that we have been able to merge with
Speaker 1: quantum mechanics. We have relativistic quantum mechanics that allows us
Speaker 1: to do these calculations, or quantum field theory also has
Speaker 1: special relativity built in. So special relativity and quantum mechanics
Speaker 1: do play very nicely together.
Speaker 2: Aw that's great, okay. And so when they're playing together,
Speaker 2: why does them playing together change?
Speaker 1: Yeah? Great question. And since this paper came out, been
Speaker 1: a lot of coverage of this result in popular media,
Speaker 1: and I read all of them, and they're all wrong.
Speaker 1: What they all get the physics wrong.
Speaker 2: Let's take a break, and when we come back, you're
Speaker 2: gonna tell us how we get it right. Before the break,
Speaker 2: Daniel was telling us that he's been reading a bunch
Speaker 2: of popsye articles that attempt to merge quantum mechanics and
Speaker 2: special relativity and that all of their explanations are wrong.
Speaker 2: So let's talk about the wrong explanations first.
Speaker 1: Yeah, and these are not just popsye articles in like,
Speaker 1: you know, science News, dot buzz or something.
Speaker 2: I hate science.
Speaker 1: People are constantly boarding me articles from sites with names
Speaker 1: like that and being like is this true? And I'm like, man,
Speaker 1: why are you gonna read in that site? You know?
Speaker 1: But there's some pretty venerable places that have put out
Speaker 1: press releases and articles about this that get it wrong,
Speaker 1: and they all repeat the same nonsense. They all repeat
Speaker 1: this business about how electrons, when they approach the speed
Speaker 1: of light, gain mass become more massive. That's the heart
Speaker 1: of their explanation. And number one, that's not true. Things
Speaker 1: do not gain mass as they approach the speed of light.
Speaker 1: This concept of relativistic mass is outdated, it's not appropriate.
Speaker 1: It was Einstein's mistake. We talked about it recently on
Speaker 1: the podcast. We can dig in it again in a moment. Also,
Speaker 1: it doesn't really explain why mercury has a lower melting point,
Speaker 1: you know, electrons having more mass doesn't answer this question.
Speaker 1: I actually reached out to a chemist here at UCI
Speaker 1: to ask him about this, and he said, quote, most
Speaker 1: chemists know little about relativity, and I suspect that makes
Speaker 1: them more likely to swallow the pop side buzzwords.
Speaker 2: Oh, I'm surprised any chemist was willing to talk to
Speaker 2: e given our reputations.
Speaker 1: Well, maybe he's not a listener to the podcast. So
Speaker 1: let's unpack that for a minute. Why do I say
Speaker 1: that it's not true that electrons increase their mass because
Speaker 1: you hear that everywhere, right, And it's a very popular
Speaker 1: thing to say because it sounds weird. It's one of
Speaker 1: these things that people say a lot because that has
Speaker 1: an impact on your mind. But it doesn't really actually
Speaker 1: make sense. It just sounds cool. And we talked about
Speaker 1: on the podcast why that doesn't really make sense and
Speaker 1: why relativistic mass isn't even a useful concept. It doesn't
Speaker 1: make sense because if mass depends on velocity. Velocity is
Speaker 1: three directions, right, it's a vector. You can velocity in
Speaker 1: one direction, another direction, a third direction. There's three dimensions
Speaker 1: of space. If three dimensions of velocity. If mass depends
Speaker 1: on velocity, then mass also has three dimensions. Then you
Speaker 1: would have like a different mass in each direction. It's weird,
Speaker 1: it doesn't make any sense. It's not what we think
Speaker 1: about as mass, and mostly it's misleading people think that
Speaker 1: something weird and mystical is happening, like as the electron
Speaker 1: is a approaching the speed of light, it's growing and
Speaker 1: mass like it's getting more stuffed to it in some
Speaker 1: weird way. That's not what's happening at all. What's happening
Speaker 1: instead is that as electrons approach the speed of light
Speaker 1: relative to an object, our intuition about the relationship between
Speaker 1: energy and velocity fails down here at very low velocity
Speaker 1: is the surface of the Earth. When we're running around
Speaker 1: at low speeds and driving, and what we think our
Speaker 1: high speeds were really pretty slow compared to the speed
Speaker 1: of light. We think that as you add energy, velocity
Speaker 1: goes up to and they go up together, right, But
Speaker 1: what happens as you approach the speed of light is
Speaker 1: energy can keep going up. There's no limit to energy,
Speaker 1: but a velocity is limited to the speed of light,
Speaker 1: and so as you add energy to something, it's velocity
Speaker 1: doesn't go up by as much, and so that sounds
Speaker 1: sort of like, oh, it's getting more massive because it's
Speaker 1: harder to get it to go faster. Right, It's really
Speaker 1: just a relationship between velocity and energy that gets more
Speaker 1: complicated near the speed of light. So it's not like
Speaker 1: a useful things we can use energy. Energy contains all
Speaker 1: the same information as relativistic mass, and energy is not
Speaker 1: as misleading. It doesn't give people the impression that, like
Speaker 1: the electrons getting more stuff to it somehow, So it's
Speaker 1: not a useful concept and it's misleading. And in this case,
Speaker 1: it doesn't explain why mercury would have a lower melting point.
Speaker 1: You know, having more mass would mean it would take
Speaker 1: more energy to get you to higher velocities. But these
Speaker 1: things are moving at very very high velocities, so that
Speaker 1: would imply that they have even more energy, which would
Speaker 1: push them out from the center and would be easier
Speaker 1: for them to nab by other atoms. And so it
Speaker 1: sort of goes in the wrong direction as far as
Speaker 1: I understand.
Speaker 2: It, all right, so I am definitely not going to
Speaker 2: be reading science dot buzz or what was it, science
Speaker 2: News dot bus because they clearly got this wrong. And
Speaker 2: you know, you mentioned that everybody was talking about it,
Speaker 2: and you know when my daughter came home from school
Speaker 2: and was like, electrons increase their mass as they approached
Speaker 2: the speed of light, I was like, I'm so disappointed
Speaker 2: in you, Ada, But so what is the right explanation?
Speaker 1: So there is an explanation. It's not like as simple
Speaker 1: and as compact a story. As the electron gets weirdly massive.
Speaker 1: The answer is that to figure out where the electrons go,
Speaker 1: you have to solve the equations, and the equations depend
Speaker 1: on a lot of stuff, and the solutions to those equations,
Speaker 1: you know, the energies that the electrons are happy to
Speaker 1: be at are different if you include relativity than if
Speaker 1: you don't. And if you include relativity, you get electrons
Speaker 1: with smaller orbits. Right, they're still moving at very very
Speaker 1: high speeds, but they have tighter orbits. They're closer to mercury. Essentially,
Speaker 1: they have lower energy than without relativity, and so they
Speaker 1: have tighter orbits at these very high velocities, and because
Speaker 1: they have tighter orbits, mercury is able to hold on
Speaker 1: to these electrons even more tightly than its friends in
Speaker 1: the same column zinc and cadmium, for example. And so
Speaker 1: if you turn off relativity, then it relaxes a little
Speaker 1: bit and these electron get larger. If you turn on relativity,
Speaker 1: then the electron orbitals shrink a little bit. And I
Speaker 1: went back to that chemist and I asked him, hey,
Speaker 1: do you have an intuitive explanation for what's going on here?
Speaker 1: Is there a nice little story in the same vein
Speaker 1: as like, hey, electrons get more mass, but actually correct?
Speaker 1: And he said, look, chemistry is complicated. The answer is no,
Speaker 1: there isn't a nice simple explanation. It's just that when
Speaker 1: you include these effects, the first order relativistic correction if
Speaker 1: you're doing perturbation theory, is to reduce the energy of
Speaker 1: this shell. And it turns out to be a really
Speaker 1: hard calculation, which is why people only recently were able
Speaker 1: to do it. You have to model a bunch of
Speaker 1: atoms altogether to figure out the bonds between them and
Speaker 1: all of the electrons around those atoms, and this is
Speaker 1: a really hard thing to do you need really powerful computers?
Speaker 1: And then adding the relativistic pieces means every time you
Speaker 1: want to move your system forward in time, you have
Speaker 1: to do a bunch more complicated calculations. Like relativity makes
Speaker 1: everything harder, Like not only is it harder to think
Speaker 1: about it, but it's also harder to get our computers
Speaker 1: to predict. There's like more steps in each calculation, more
Speaker 1: multiplications and divisions and square roots and all sorts of
Speaker 1: really weird stuff. But it's these relativistic effects which push
Speaker 1: the prediction from chemistry down below room temperature. So there's
Speaker 1: a recent paper and they predict that the melting point
Speaker 1: of mercury should be negative twenty three C. So without
Speaker 1: relativity they predict eighty two c. With relativity, they predict
Speaker 1: negative twenty three c. Now the real value is negative
Speaker 1: thirty nine CE. So they're still not getting it right.
Speaker 1: There's still more to understand there, probably second third order
Speaker 1: relativistic corrections, more detailed, accurate predictions, but they have gotten
Speaker 1: it down below room temperature. And so this we're convinced
Speaker 1: is the explanation for why mercury is a liquid or
Speaker 1: room temperature. It's relativity.
Speaker 2: So that is super cool. So mercury has an atomic
Speaker 2: number of eighty and it's got a really low melting point,
Speaker 2: But why doesn't everything past eighty also have a really
Speaker 2: low melting point. It still feels like mercury isn't all
Speaker 2: relative to everything else.
Speaker 1: Yeah, well it sort of does, like if you keep going.
Speaker 1: You know, lead, for example, has a melting point of
Speaker 1: three hundred and twenty. That's not that high. It's a
Speaker 1: lot lower than silver and gold, and that's because it's
Speaker 1: really heavy and it has these relativistic effects. But also
Speaker 1: it doesn't have a complete shell, so it's much higher
Speaker 1: than mercury because it doesn't have a complete shell. If
Speaker 1: you get all the way over to the end of
Speaker 1: the periodic table, if like xenon, its melting point is
Speaker 1: like negative one hundred C and radon is like negative seventy. See,
Speaker 1: these things are gas at room temperature, so you see
Speaker 1: those effects. As you move down the periodic table, melting
Speaker 1: points are shrinking, and one of these reasons is relativity.
Speaker 1: But it's not the only thing that's.
Speaker 2: Happening, right, Okay, So it's the combination of the shells
Speaker 2: being filled, how tightly those shells are held by the
Speaker 2: nucleus being heavy, and the fact that that heavy nucleus
Speaker 2: is causing the electrons to move faster. Now you have
Speaker 2: really sativistic effects, and all three of those things come
Speaker 2: together with mercury to impact a s melting point more
Speaker 2: than anything else. So like, for example, if you move
Speaker 2: to ten, ten, yes, still has that relativistic effect going on,
Speaker 2: but now you have one electron in the outer shell,
Speaker 2: and so it's wanting to react to stuff, and so
Speaker 2: now you're in a different world altogether, and that's why
Speaker 2: it doesn't have such a low melting point.
Speaker 1: I think maybe you're thinking about thallium, which is the
Speaker 1: next one over for mercury, and it looks like ten
Speaker 1: but it's actually a TL. But otherwise, yes, exactly, yeah,
Speaker 1: And so that's why thallium is like three one hundred
Speaker 1: and fifty degrees higher melting point than mercury, because it's
Speaker 1: got this one extra electron which we're very happy to
Speaker 1: bond with other thallium atoms.
Speaker 2: My annual eye appointment is next week, and so maybe
Speaker 2: in a few weeks I'll be able to read the
Speaker 2: periodic table.
Speaker 1: But even if it was TI, that wouldn't be ten
Speaker 1: ten is s n right because it's got some weird
Speaker 1: Latin name.
Speaker 2: Oh, how embarrassing. How embarrassing.
Speaker 1: But you're right that there are relativistic effects all over
Speaker 1: at the bottom of the periodic table, for example gold.
Speaker 1: Why is gold beautiful and gold colored? Whereas silver, which
Speaker 1: has the same electron structure and is one above and
Speaker 1: in the same column, is basically colorless. It's you know, silver.
Speaker 1: The answer is relativity. The color of an element depends
Speaker 1: on the photons it will emit and absorb, which depend
Speaker 1: on the spacing between the energy levels, and relativity changes
Speaker 1: those energy levels in gold much more than they do
Speaker 1: in silver, which makes it gold colored. Without relativity, gold
Speaker 1: would look like silver.
Speaker 2: Oh my gosh, I know so much cool stuff happening
Speaker 2: with relativity.
Speaker 1: People always say relativity is beautiful. Now you know why
Speaker 1: it's gold.
Speaker 2: People are always saying that, like it's common on T
Speaker 2: shirts and stuff like that.
Speaker 1: People are saying that you're being ironic, but I'm not.
Speaker 1: Relativity really is beautiful.
Speaker 2: I do think it's beautiful. I do, And this has
Speaker 2: been super cool. So how recent is this incorporation of
Speaker 2: special relativity into our understanding of what's happening in the
Speaker 2: periodic table. Is this something I think I'm remembering you said,
Speaker 2: we've kind of known about it for a while, but
Speaker 2: haven't been able to calculate it until recently, Like, how
Speaker 2: recently have we started incorporating this stuff in there?
Speaker 1: So you know, we've known about quantum mechanics for about
Speaker 1: one hundred years and relativity for about one hundred years.
Speaker 1: They were merged together into relativistic quantum mechanics only a
Speaker 1: few decades after the birth of both of those theories,
Speaker 1: so that's been for a long time. But in order
Speaker 1: to do this calculation requires a lot of computing, So
Speaker 1: it's only about ten years ago the people were able
Speaker 1: to do this calculation and predict the melting point of
Speaker 1: mercury more accurately than eighty two c And so yeah,
Speaker 1: this is a pretty recent calculation.
Speaker 2: It's a cool time to be alive.
Speaker 1: It is a cool time to be alive. But while
Speaker 1: mercury is amazing and gorgeous and fascinating, please don't play
Speaker 1: with it, don't drink it, don't throw it at your sister.
Speaker 2: You probably don't want to put a vial of it
Speaker 2: on your neck.
Speaker 1: Though it turned out pretty well for you. Kelly.
Speaker 2: That was probably one of the less dangerous things kids
Speaker 2: like me were doing in the nineties. We were sort of
Speaker 2: free ranging around our neighborhoods. All right, well, I'm going
Speaker 2: to get my special. Relativity is awesome t shirt M
Speaker 2: because you've convinced me and I look forward to talking
Speaker 2: to you next week.
Speaker 1: That was good, and so for those few folks out
Speaker 1: there keeping track, relativity has now explained two totally different
Speaker 1: kinds of mercury, both the orbit of the planet mercury
Speaker 1: and the melting point of the element mercury. Relativity is
Speaker 1: all over it.
Speaker 2: Ah. You know, actually, when I read your intro, I
Speaker 2: thought to myself, I don't know the story about how
Speaker 2: relativity predicted Mercury's orbit. Should that be another episode? Is
Speaker 2: there a thirty second version? Or should we do a
Speaker 2: future episode?
Speaker 1: Future episode? Let's do it.
Speaker 2: Future episode locked in? All right, Thanks for listening. If
Speaker 2: you want to get in touch, please send us an
Speaker 2: email at questions at Daniel and Kelly dot org. We
Speaker 2: can't wait to hear from you.
Speaker 1: Thanks for staying with us for this Chemistry episode.
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