Lecture 1: Introduction and the Chemistry of the Periodic Table

Lecture 1: Introduction and the chemistry of the periodic table Summary “Never trust an atom, they make everything up,” is a classic chemistry joke that also happens to be so true, but if we want to know which elements comprise our materials of interest, then we need to know how these elements interact with one another, how they are structured, and how the material was processed to achieve this structure. To truly answer these questions, investigators in the last few centuries have made use of the scientific method. This involves asking questions, gathering and examining evidence, identifying explanations, and re-testing. One of the most exciting questions in the history of chemistry was that of the atom—Democritus and Leucippus hypothesized indivisible building blocks of the universe (though now we know that atoms can be broken down into even smaller “subatomic particles”). Robert Boyle, in his quest to identify different atoms, studied metal ores (naturally occurring rocks containing metal impurities) and succeeded in separating a large number of elements, including many metals. As the list of discovered atoms grew, scientists also began studying their categorization. For example, Antoine Lavoisier named four property-based categories for the 33 elements he identified: Gases, Non-Metals, Metals, and Earths. John Dalton identified 36 different elements, and designed a graphical symbol to represent each of them. In this lecture we introduced the concept of chemical reaction balancing, which involves adding coefficients to the reactants and/or products in the reaction to ensure that there are equal numbers of each type of atom on the left- and right-hand sides of the arrow. This is necessary because of the law of conservation of mass, which states that nothing is created or destroyed at the atomic level, so the mass of the reactants equals the mass of the products. Rather, atoms can be rearranged to form different molecules. The first chemical reaction we balanced was a combustion reaction, which is a reaction in which a carbonaceous material burns in the presence of oxygen. We found the limiting reagent for this reaction, which is the reacting species (atom or molecule) that is used up first. The yield of the reaction is the amount of product formed. Dalton stated that atoms of a given element have a particular weight and other distinguishing characteristics. He proposed the law of multiple proportions, which says that when two elements react to form a series of compounds, the ratios of masses of the 2nd element per gram to the 1st can be expressed as ratios of integers. Why this matters In this first lecture, we started talking about the discovery of the elements. Well, I don’t mean to give anything away, but there aren’t going to be all that many of them in the end. In fact, to date we’ve got 118 on the official roster, but if we consider which ones we can use to make stuff for humans that number is lower, more like 80 or 90. How many elements do you think there are in your cell phone? It depends on the phone, but in mine there are 64 different elements! That’s more than two thirds of all of the ones we could even have used and it’s incredible to think about. Because of this massive design potential, the world we live in has completely changed. As a Materials Scientist, I love that we have this tradition (shout out to Danish scholar Christian J. Thomsen) of naming the age we live in by the material that mattered most during that age. But as a Materials Scientist, I also love that we’ll never be able to do that again. The reason is that we truly live in a new era, one where we can realize the dream of Richard Feynman, who in his famous speech “There’s Plenty of Room at the Bottom” put forth the vision for atomicscale design and nanotechnology 30 years ahead of its time. Today, we routinely control both the choice of elements as well as their structure as they come together to make materials do things we never thought possible even just 10 years ago! In other words, we control their chemistry at the atomic scale. Images of stone arrows, bronze pot, industrial age, plastic bottles, silicon chip © sources unknown. This gets to why this is so cool (and, you guessed it, why it matters). You see, so many of our current global challenges – whether in energy, health, or the environment – have a bottleneck that occurs because of the material that makes up a central part of the technology (in some devices it’s called the “active layer”). That means that by “simply” choosing or making a different material, one has the potential to completely change the properties, cost, and manufacturability of the technology. This is unlike a previous revolution around silicon where we went from a cost of $1 per transistor in 1965 to $0.00000001 per transistor in 2015. Talk about a learning curve! That was primarily due to advances in processing of the same element, silicon, to get to smaller and smaller components. More than a billion transistors now fit nicely on a single chip. Unlike this dramatic age of silicon, many of the next technology revolutions will rely on changing the material itself: in some cases, completely. We now live in the Materials Design Age, which has come just in time since it converges with very pressing challenges on a global scale that will rely on new materials to be solved. And this is why the discovery of these elements matters so much. They are our playground and the basis from which we will make the next set of technologies to change the world for the better. Why this employs In this section, we’ll discuss how the material in each lecture connects to real jobs. I’m trying it out this year for the first time, and since I likely won’t have time to spend on it in lecture, this document is the only place you’ll find it. In Why This Matters, I passionately believe that each lecture can and should be connected to some larger-scale challenge, or innovation, or inspiration. In Why This Employs, my goal is to connect each lecture with a possible field of employment. Similar to Why This Matters, this is not meant to be exhaustive but rather illustrative, to give you another way in 6 which the material you’re learning has value beyond the classroom and connects to something, in this case a job. We spent half of this first lecture talking about the class structure, not just administratively (what’s graded, what’s not, etc) but also pedagogically (the different components, how they come together to provide a learning experience, etc.). Thinking about how to teach better, and how students learn, and how new technologies should or should not be a part of this, is a wonderfully rich area of employment. If you’re interested in learning more, check out MIT’s Teaching and Learning Lab or some of the cool initiatives in education like EdX, NEET, or the “superUROP” programs. Another employment direction related to this lecture is the discovery of new elements. Here, we examined how the earliest chemists attempted to identify elements. This came down to smashing, burning, boiling, reacting, etc. It turns out that’s still a thing, only in modern times all this reacting occurs with much bigger pieces of equipment and much larger teams of people. The next element yet to be discovered (at the time of writing, that would mean the 119th known element) will likely not have a very long lifetime, and will be very difficult to make in large quantities. But pushing the boundaries between what we have found naturally and what we can make synthetically as it relates to the fundamental building blocks of the universe. . . well, that’s a pretty exciting thing to do. And given the prediction by some that an “island of stability” exists for heavier elements that have yet to be made, it’s possible that an entirely new era of chemistry awaits such discoveries. The last example I’ll give for employment relates to the idea of the metal ores that I mentioned earlier in this lecture. Remember that this is where Dalton and many others were discovering those new elements. Basically, you take a rock and carefully break it up and viola, you get Fe out of it (ok, it’s a bit more complicated than that, but that’s the idea). It turns out that quite often the metal atom is locked up pretty tightly in the form of an “oxide” (yes, that means bonded to oxygen, but we’ll get to that in a few lectures). The point is that extracting metals like aluminum from rocks takes an enormous amount of energy, which means it requires a lot of burning of fossil fuels. What if you could come up with a new, much “greener” way to get metals or minerals in their pure form out of the rocks from which they originate? This would be a very big deal. Mining metals and minerals involves massive teams of engineers who cover a wide array of jobs from figuring out where to mine, to characterization of the starting materials, to optimizing extraction chemistry, to working on new ways to do that more efficiently. Example Problems 1. In this lecture, you witnessed my passion for pyrotechnics. a) Write and balance the chemical reaction for a similar process, the combustion of propane (C3 H8 ). b) If you have 500g of propane, how many moles do you have? How many molecules? Solutions 1. a) C3 H8 + 5O2 → 3CO2 + 4H2 O b) First, find the molar mass of propane. 3 ∗ 12g/mol + 8 ∗ 1g/mol = 44g/mol Use the grams given and the molar mass to convert to moles: 500/44 = 11.36mol