Episode 25: Chemistry – Challenges and Solutions
Today, we have a special episode, Explore Chemistry: Challenges and Solutions – a video course designed to learn general chemistry concepts using real-life challenges in energy, materials development, biochemistry, and the environment. The following episode highlights an excerpt from Chemistry: Challenges and Solutions, where learners explore concepts in chemistry by providing a strong foundation for learners through a dynamic video course with each video hosted by a different working chemist to show a diversity of chemistry professionals and the challenges chemistry is addressing for society.
The interview has been edited for length and clarity.
Matter and the Rise of Atomic Theory: The Art of the Meticulous [02:00]
Narrator: It takes just over 100 elements to make the entire known universe from our morning breakfast to our commute to school or work, and even for our entertainment. Combining elements to improve our world is at the heart of what it means to be human.
Michael Meyer: Chemistry is something that we are and also something that we do. Humans are unique in the sense that we do chemistry. We deliberately manipulate matter for our own purposes.
Ahmed Ragad: Where did chemistry start? It’s a question that’s almost impossible to answer because when you think about it chemistry is just part of our everyday life.
Narrator: We all practice chemistry, usually without being aware of it. Our ancestors made cave drawings from animal fat, charcoal and even blood. We turn iron into steel, flour into bread, food into fuel, and water into electricity. There is almost no limit to the ways in which we transmute matter. Discovering, refining and combining new substances has evolved and grown into what it is for us today – the world we live in, a world of chemistry.
Chirstopher Morse: Here we are at a beach. In the middle of this beautiful natural setting, chemistry probably isn’t the first thing that comes to mind.
Hi, I’m Chris Morse and I’m a chemist, so why are we here at a beach? Because it’s full of sand. But I don’t see sand. I see silicon dioxide. While that might sound scary, all it means is that there’s one atom of silicon and two atoms of oxygen. Even the Ancient Romans could convert this into glass. The sand on this beach can be separated with modern technologies into silicon and oxygen and that silicon can be converted into computers, solar panels, and even my smart phone.
Nowadays, we would say that we live in a silicon age. Before that there was an iron age, a bronze age, a stone age. The one thing that’s always been true is humans have named their periods of history after the chemistry they’ve been doing at the time. So over thousands of years chemistry has reached the point where we can take the sand on this beach and convert it into the chemical component that is the center of my cell phone.
Atoms and Light: Exploring Atomic and Electronic Structure [4:53]
Michael McCarthy: Atoms are tiny. 100,000 atoms could fit across a human hair. This means that we cannot hope to observe them with the naked eye.
Hi, I’m Michael McCarthy and I’m an astrochemist studying the chemical composition of the universe. My work overlaps astronomy with chemistry. Astrochemistry is the study of elements and molecules in the universe. We investigate how they interact with light and with each other. My research is related to the atomic and chemical composition, evolution, and fate of molecular gas clouds between stars. It is from these clouds that solar systems form.
It’s important for me to understand the structure of atoms and molecules and the ways that they interact with light. Spectroscopy is the tool I use. While we think of light as something that shines or glows, light includes visible light as well as ultraviolet, infrared, radio, and X-rays. All of the forms of light together make up what we call the electromagnetic spectrum. We can explore matter by looking at the light it absorbs under some conditions, or the light it emits in others.
Wayne Strattman: I’m Wayne Strattman. The work I do as an artist relates to chemistry in that I’m mixing gases and various vapors together in various proportions and pressures and then exciting them, giving them energy. I’m specifically looking for visual effects – kinetic effects.
By varying the pressure, I can get a variety of different effects and motions. I can make it move like lightning, or I can just make it a soft subtle glow. When we put electricity into gas, depending on the gas, that gives a characteristic single color to the gas. Neon, orange-red, and argon, that pastel-purple, and in the case of xenon gas, you get the characteristic color of this purplish-blue. Well, I always like to say in my business that we’re trying to be masters of 19th-century technology. Because that’s where this all started.
Narrator: In the late 1800s, with a new ability to effectively remove the air from glass tubes, creating a more effective vacuum, a new phenomenon was observed. When an electric current was applied to the tube it appeared that something was being emitted from one end, hitting the other end. It originated at the negative terminal, or cathode, and traveled to the positive end, or anode. Scientists called the phenomenon, a cathode ray and the devices that produced them, cathode ray tubes.
Scientists like the British physicist J.J. Thomson performed experiments with cathode ray tubes to try to understand what the so-called cathode rays were.
Wolfgang Rueckner: What they found was that a magnetic field affects these cathode rays. For example, bringing a south pole near this beam deflects it upward. And bringing a north pole, if I flip the magnet around, bring it towards the beam, deflects it downward. Likewise, if we apply an electric field to this, if I make this end positive and this end negative, if these are negatively charged particles, they will get attracted to the positive plate inside here. Like this. And if I reverse the polarity, then they get deflected the other way, because now the bottom is positive.
So, we can deflect these cathode rays with electric forces or magnetic forces, or both. In fact, we can balance those two forces. Have one undo what the other one does. And make the beam go straight. That’s what J.J. Thomson did and was able then to figure out the ratio of charge of these cathode rays to their mass. He found out the mass was exceedingly small and the charge, we know, is the charge of an electron.
Narrator: Thomson measured how much the cathode ray was deflected in both electric and magnetic fields of known strength. Using these measurements and the physics of the time, he was able to figure out the ratio of the charge on the electron to its mass. While Thomson was not able to measure the charge or mass of the electron, he laid the groundwork for future scientists to do so.
Michael McCarthy: Cathode ray tubes have not been the subject of research for many years. But the technology is still very useful. Cathode ray tubes in fact have been used in televisions for nearly a century. In my laboratory we use oscilloscopes and spectrum analyzers, all of which use cathode rays to display and analyze electromagnetic signals, which are used in many of our experiments.
Narrator: J.J. Thomson deduced from his experiments that there are different parts of an atom, with positive and negative charges. While he is credited with discovering electrons, Thomson didn’t understand their arrangement within the atom. His model, which he called the “Plum Pudding” model, didn’t have a nucleus. In his model the positive charge filled the atom, and the negative charge came from points scattered evenly throughout – in his analogy, the plums.
Michael McCarthy: It’s important to understand that atomic models are more like analogies than perfect representations. Atoms are so different from things we know from our everyday experiences, that any physical representation is bound to have flaws. No model is perfect, but good models help us understand better the structure of atoms.
Organizing Atoms and Electrons: The Periodic Table [11:19]
Julie Gostic: Basically, the periodic table is our lifeline.
Ken Moody: As a chemist, I use the periodic table on a daily basis. All chemists would find useful information in the periodic table.
Daniel Rosenberg: And now we’re going to react potassium with water.
Sam Kean: The elements are the basic building blocks of the universe. And the periodic table orders them in a very clever way, but the periodic table, contrary to what you might believe, isn’t set in stone.
Narrator: It is an extraordinary achievement that nearly 118 elements, either naturally occurring or synthesized, have been identified so far. Many elements have been known for millennia, but scientists continue to isolate new ones today.
Julie Gostic: We are looking at the periodic table and we are saying, it should be right there. And then, actually, maybe it is, maybe it isn’t. So, it’s a big guessing game until you actually produce it.
Ken Moody: We’re trying to fill in the blanks and we’re also trying to figure out how many more blanks there are.
Mala Radhakrishnan: I’m Mala Radhakrishnan, a professor of Chemistry at Wellesley College. I am interested in the periodic table of elements, just like I’m interested in music. Both music and chemistry rely upon patterns and rules to form universal languages. The periodic table of the elements is a fundamental tool that all chemists use. The genius of the periodic table is in its organization.
Sam Kean: Now there are lots of other arrangements out there, and in fact there are some really ingenious arrangements. One that I really enjoy has hydrogen at the center and then there are other elements, spiraling around it like a galaxy. There are some that look kind of like board games, instead of being nice boxes they kind of wander around the board. There are some that are in 3-D; one of them I saw has a nice double helix motif. There are pyramidal shaped ones, there’s honeycomb shaped ones. It’s really kind of spectacular. But they’re not always the easiest when you’re trying to learn the periodic table or to teach the periodic table.
Mala Radhakrishnan: By 1869, a total of 63 naturally occurring elements had been discovered, just by exploring the environment. As the number of known elements grew, scientists recognized patterns in their chemical properties and began to develop classification schemes.
Narrator: Chemists in the 19th century were not aware of electrons or protons. Most of their information came from measurement of atomic masses and other observed physical and chemical properties. Dmitri Mendeleev is often considered the father of the periodic table. The arrangement he eventually came up with was so successful that it has endured through the discovery of dozens more elements, as well as new ways of understanding atoms that Mendeleev and his contemporaries could never have imagined.
Mala Radhakrishnan: Mendeleev arranged his periodic table according to the masses of the elements. There is a reason why his table is called a periodic table, and not just a chart of the elements. “Periodic” refers to patterns or cycles.
Each row of the table represents a pattern of chemical properties that repeats in the row beneath it. In a given column elements are all at the same point in that cycle, and therefore have similar chemical properties.
Let’s take a look at the fourth row or period. Starting with potassium, which has the largest atoms in its period, atoms generally get smaller as you move across a period. Also, elements show differing levels of reactivity across a period. While potassium is very reactive, at the other end of this period is krypton, a noble gas, the least reactive element in its period. In between, the reactivities are high or low depending on which column or group the element is in.
Next, in period five, the first element is rubidium. Rubidium is the most reactive element in its period. Again, as we move across, the atoms are trending smaller in size, and the reactivities go up and down, but in the same pattern as the period above.
In this way patterns repeat in each period, resulting in similar properties within each group. In our example, the first group contains highly reactive elements including potassium and rubidium. The last group, the Noble gases contains generally unreactive elements, including krypton and xenon.
Sam Kean: The next big breakthrough with the periodic table came right before World War I, in England, with a man named Henry Moseley. He found that the number of protons in the nucleus corresponded exactly with an element’s spot on the periodic table.
Mala Radhakrishnan: Moseley arranged his periodic table according to atomic number. A few years later it was confirmed that this atomic number was based on the number of protons in each element. The atomic number, the number of an atom’s protons, is how we still order the elements. Each box contains information about the atoms of one element. Typically, you will see the one or two letter atomic symbol, its atomic number, and its average atomic mass. The atomic symbol for sodium, for example, is Na, and its atomic number, its number of protons, is 11. When we arrange the table by atomic number, it generally coincides with Mendeleev’s table, which was arranged before protons were even discovered. So, this suggests a link between atomic structure and observed periodic properties such as reactivity.
Equilibrium and Advanced Thermodynamics: Balance in Chemical Reactions [18:10]
Narrator: We often think of a chemical reaction as having a distinct beginning and end like a race. And there are many chemical reactions that behave this way. But most reactions never stop. Instead, they reach a steady state of constant motion – a state of chemical equilibrium. Billions of equilibrium reactions are occurring in our bodies every second.
Daniel Deschler: That’s fascinating, and that’s what we do in medicine. We try to take this human being that’s in this functioning equilibrium and realize when there’s something eschew, how we can make it better.
Narrator: And over 100 years ago, the successful manipulation of an equilibrium reaction on the industrial scale would forever change the course of human history.
Thomas Hager: This discovery is creating the food that is feeding almost half the people on earth. It’s hard to imagine a technology that’s more important than that.
Narrator: Saving lives and feeding the world. Just two of the many benefits gained by mastering the delicate and dynamic nature of chemical equilibrium.
Wilton Virgo: What can rust tell us about chemical reactions?
Hi, I’m Wilton Virgo, a Chemistry professor at Wellesley College. What is rust? When steel, a mixture of iron and carbon, like the metal in this sculpture, meets oxygen and water, the iron in the steel reacts. This causes the iron to become a hydrated iron oxide, which we call rust.
Most of us are familiar enough with rusting to understand that this is a chemical reaction that proceeds all on its own. Chemists refer to this type of reaction as spontaneous. And there are many chemical reactions in the world that are spontaneous. When that’s the case, the reaction in the opposite direction is not spontaneous. Let’s look again at our example with iron.
To make steel, we need pure iron, or as close to pure iron as we can get. But because iron spontaneously reacts with oxygen, iron in its pure metallic form is nearly impossible to find on Earth. As a matter of fact, most iron on the planet exists as iron oxides, which we call iron ore. So, what do we need to do to get the iron and oxygen to separate? We need to get the reaction to go in the non-spontaneous direction, and this takes a lot of chemical work, because it is a reaction that does not really want to happen. And that, for the most part, is what’s going on in a steel mill.
Determining which way, a chemical reaction will go is an important part of thermodynamics. However, this is not always a “one way or the other” determination. It’s true that some reactions can only go in one direction, but many reactions proceed in both directions, and some of these will do both the forward and reverse directions dynamically at the same time. We call these last one’s equilibrium reactions.
Kinetics and Nuclear Chemistry – Rates of Reaction [22:03]
Narrator: From an instantaneous explosion to the slow rusting of iron, the rates at which different chemical reactions proceed can vary tremendously. Chemists strive to control those rates. Sometimes, like with the rotting of food, they want to slow them down, but often the goal is to speed them up. One way to do this is to use a catalyst.
Amir Hoveyda: The catalyst is a magician’s wand. If a magician is standing by a black hat, nothing is in the hat until he touches the hat with the wand and the rabbit comes out. That’s what catalysts can do.
Narrator: But the rate of some chemical reactions is unchangeable. This is the case with nuclear or radioactive decay. Using PET scans, we can take advantage of this steady constant rate to detect disease.
Georges El-Fakhri: It is one of the most sensitive tools we have, and it saves lives.
Narrator: The study of the rates of chemical reactions is called chemical kinetics and it is about more than just speed. It is about understanding the intricate, elegant and sublime story that is a chemical reaction.
Wilton Virgo: Hi, I’m Wilton Virgo, a chemistry professor at Wellesley College. If you think of this bumper car as a molecule, it cannot react with another molecule unless it collides with it.
One way to increase the chances of a collision happening is to increase the total number of molecules present. And this is one strategy chemists use to speed up a chemical reaction – we increase the concentrations of reactants. But just because two molecules collide, they still may not react with one another. The reactant molecules must collide with enough energy to break their old bonds and reach a temporary state of higher energy.
Chemists often refer to this as a hill that you must get over, and for a given reaction, the energy needed to get over that hill is referred to as that reaction’s activation energy.
The activation energy can be high or low, or anywhere in between depending upon the specific reaction. One way to get over that hill and speed up that reaction is to raise the temperature.
Let’s take a look at a demonstration of activation energy.
Daniel Rosenberg: In this test tube I have a mixture of hydrogen and chlorine gases. Now hydrogen and chlorine would like to react to form hydrogen chloride, but in the dark, in this test tube, the hydrogen and the chlorine can coexist without reacting for a very long time. The way to get them to react is by giving them enough energy to get started and that energy is called activation energy. I have a dark cloth over this test tube because for this reaction, light can provide the activation energy. And we’re going to use a spectrum of LEDs to test what that activation energy is.
We’re going to start with red, and red light has the lowest frequency and the smallest amount of energy per photon of these LEDs. Then we’re going to move to yellow, which has a slightly higher frequency and a little more energy. Green, which is about in the middle of the spectrum. Blue, which is at the high frequency end of the spectrum and has a lot of energy per photon, and finally ultraviolet light, which is beyond the end of the spectrum and has the most energy per photon.
So, without further ado. Red light, yellow, green; even though it’s bright, green light doesn’t have enough energy to start this reaction going. Blue light. Ultraviolet. BAM! Sets it right off. BAM!
So, what we’ve demonstrated is that it takes the energy of ultraviolet light to set this reaction going. Now that is some activation energy!
Wilton Virgo: Raising the temperature is not the only way to increase the speed of a reaction or the likelihood that it will occur. Instead of trying to get over the hill, another option is to create an alternative pathway that requires less energy – a smaller hill. And this can be done with a catalyst.
You can think of a catalyst as kind of like this train. If I were to walk from one side of this amusement park to the other, it would take about twenty minutes. But using my catalyst, the train, I have an alternative pathway. And it only takes about ten minutes to achieve the same results. And the train, after it drops me off, is available to transport more people around the park. A catalyst acts in the same manner – it changes during the reaction, but once the reaction is over the catalyst returns to its original state and can be used in subsequent reactions.
Modern Materials and the Solid State: Crystals, Polymers, and Alloys [28:37]
Narrator: We often think of chemistry as dissolving, precipitating, evaporating, or condensing. In fact, many chemical or physical reactions involve fluids – liquids and gases. But look around most of the matter we use in daily life – our food, our clothes, the ground we walk on, is solid. Chemists are engineering new solid materials every day. Whether crystals, polymers, or advanced metal alloys, these materials help us to explore the universe, and make advances in healthcare.
Trevor Castor: With drugs being encapsulated in polymers, taking insulin, will be like eating food.
Narrator: These new materials are all governed by the chemistry of the solid state.
Ainissa Ramirez: Solids offer so many possibilities because in a solid the individual atoms, molecules, or ions are organized in definite arrangements. And there’s so many kinds of atoms to choose from. And so many possible arrangements.
Let me show you an example. Here I have a piece of metal wire. There’s nothing special about it. I can twist it; I can bend it, and it keeps its shape. In fact, that’s one of the characteristics of a solid. Solids keep their shape, while liquids and gases take the shape of their containers. But let’s see what happens when we raise its temperature. It returned to its original shape. Let’s see that again.
When I apply heat to it, it returns to its original configuration. That’s why we call it a “shape memory alloy.” It’s an alloy, or mixture of two or more different metals, that remembers its shape. In this material, the atoms can take on different arrangements, depending on the temperature. We call these phase changes.
That’s something you’re already familiar with, like when ice melts into water. At cool temperatures, the atoms of the shape memory alloy go into one phase, which looks like this. But when the metal is heated, the atoms go into a different phase, which looks like this. Why does the phase change? Remember that atoms in a solid, even though they are held in a definite arrangement, are always jiggling in place. If you increase the temperature, they jiggle more. Then they need a little more room. In a shape memory alloy, they spontaneously rearrange themselves into a more open configuration. What do we see at a macroscopic level? The material stiffens and “remembers” its original shape.
To get a better handle on the way solids work; let’s start with what holds them together – their bonds. And what better place to do that than in a mineral collection.
Raquel Alonso-Perez: The public is always very excited about the different shapes and colors of the minerals. But from a geochemist’s point of view, these shapes and colors are the results of the highly ordered atomic arrangement and chemical compositions of these natural solid substances, which are usually formed by inorganic processes, by nature.
Here we have one example, halite, which is common salt, the one we all use for cooking in our kitchen. Notice how the shape of the crystal, or what we call the external symmetry, is in the form of a cube.
So, if we look at the atomic level, what we see is the cubic arrangement of sodium, chloride, sodium, chloride. By the repetition of that unit cell, we will get the final shape of the crystal.
Narrator: Salt is one of many minerals held together by ionic bonding, a type of solid where positive and negative ions are held together by mutual Coulombic attraction in a regular pattern.
Raquel Alonso-Perez: In my research, I’m looking at garnets, this is another type of mineral with an ionic bonding and cubic symmetry, but they usually form the dodecahedron, or 12-sided habit.
Narrator: The huge variety of shapes that the crystals of minerals adopt is simply the expression of one unit cell over and over. Ionic compounds are held together by ionic bonds, but that is only one kind of bond that holds solids together. A different type of bonding holds metals together – metallic bonding.
Raquel Alonso-Perez: Gold has a different type of bonding, which is called metallic bonding, and which is responsible for these unique properties of metals such as malleability and high electroconductivity.
Narrator: The outermost electrons in a metal atom can move freely between nearby positive metal atom nuclei, as if they were a sea of negative charge; these electrons are attracted to all the positively charged nuclei, not just one. The collective attraction between the sea of electrons and the lattice of nuclei holds the metals together.
Raquel Alonso-Perez: Other types of metals, such as silver and copper, have the same type of properties. The third known type of bonding is covalent bonding, which results from the shared electrons between atoms. This type of bonding is responsible for the great stability, insolubility, and high melting point of diamonds.
Narrator: A covalent network solid is made of many atoms held together in large, regular lattices by covalent bonds.
Raquel Alonso-Perez: Covalent bonding is the strongest bonding that we know and that’s why diamonds are the hardest mineral known on Earth.
Narrator: A fourth type of solid, molecular solids, are held together by intermolecular forces, also called Van der Waals forces. These solids, unlike diamonds, are soft, low-density, and usually have low melting points.
Raquel Alonso-Perez: Graphite has a structure which consists of parallel layers of strongly bonded carbon atoms that are separated from each other by a large distance. That large distance is the result of a weak Van der Waals bonding. Because of this weakness, and these parallel layers in between, graphite can be used for many applications, especially for writing, in our pencils.