loader image
Courses

Chemistry and Our Universe, How It All Works

YEAR: 2016 | LENGTH: 60 parts (30 minutes each)  |  SOURCE: TGC

description:

Our world is ruled by chemistry. The air we breathe is nitrogen, oxygen, and trace gases. The clothing we wear is cellulose, protein, or synthetic polymers. When we take to the road, we are propelled by the combustion of hydrocarbons or the reactions inside storage batteries. Look around and everything you see is the product of chemistry—including the sunlight pouring through the window, which originates in the fusion of atoms at the core of the sun.

episodes:

 Chemistry is the study of all matter, but matter at a very particular scale-that of atoms and molecules. Professor Davis begins by outlining his approach to this enormous topic and then introduces the periodic table of elements, one of the most powerful conceptual tools ever devised.

 Chemists have convenient units for dealing with matter at the atomic scale. In this lecture, learn the origin and relative size of the angstrom to measure length, as well as the atomic mass unit, the mole for measuring quantity and the Kelvin scale for temperature.

 Light interacts with matter in crucial ways. In the first of two lectures on the nature of light, follow the debate over whether light is a wave or a particle, starting in antiquity. See how the wave theory appeared to triumph in the 19th century and led to the discovery of the electromagnetic spectrum.

 Although light has wave-like properties, it also behaves like a particle that comes in discrete units of energy, termed quanta. Learn how physicists Max Planck, Albert Einstein, and others built a revolutionary picture of light that recognizes both its wave- and particle-like nature.

 Peel back the layers of the atom to investigate what's inside. Observe how electrons, protons, and neutrons are distributed, how they give an atom its identity, and how they affect its electrical charge and atomic mass. Discover the meaning of terms such as isotope, anion, and cation.

 Starting with hydrogen, see how electrons organize themselves within the atom, depending on their energy state. Graduate from Niels Bohr's revolutionary model of the atom to Erwin Schrodinger's even more precise theory. Then, chart different electron configurations in heavier and heavier atoms.

 Return to the periodic table, introduced in Lecture 1, to practice predicting properties of elements based on their electronic structure. Then, witness what happens when three different alkali metals react with water. Theory forecasts a pronounced difference in the result. Is there?

 Turn to molecules, which are groups of atoms that make up compounds as well as some elements. Learn to calculate the empirical formula for a simple molecule and also its molecular formula, which gives the exact number of each type of atom.

 In the first of five lectures on chemical bonds, start to unravel the mystery of what joins atoms into molecules. Investigate how molecular bonds reflect the octet rule encountered in Lecture 7 and fall into four classes: ionic, covalent, polar covalent, and metallic bonds.

 Working at the turn of the 20th century, chemist Gilbert N. Lewis devised a simple method for depicting the essential blueprint of a molecule's structure. Learn how to draw Lewis structures, and use this technique to explore such concepts as formal charge and resonance.

 Take the next step beyond Lewis structures to see how atoms in a molecule are arranged in three dimensions. VSEPR theory (valence-shell electron-pair repulsion theory) provides chemists with a quick way to predict the shapes of molecules based on a few basic assumptions.

 Meet one of the fathers of modern physical chemistry, Linus Pauling. Hear about his theory of orbital hybridization, which solves some of the shortcomings of VSEPR theory by averaging the charge of electrons in different orbitals, accounting for the peculiar geometry of certain molecules.

 Discover an alternate model of chemical bonding: molecular orbital theory, developed by Friedrich Hund and Robert Mulliken. This idea explains such mysteries as why oxygen is paramagnetic. See a demonstration of oxygen's attraction to a magnet, then use molecular orbital theory to understand why this happens.

 Begin your study of chemical reactions by investigating how chemists write reactions using a highly systematized code. Next, Professor Davis introduces the "big four" types of chemical reactions: synthesis, decomposition, single displacement, and double displacement. He also shows how to translate between measurements in moles and grams.

 Stoichiometry may sound highly technical, but it is simply the relative proportions in which chemicals react. Discover how to balance a reaction equation, and learn how to solve problems involving limiting reagents, theoretical yield, percent yield, and optimized reactions.

 Consider how atoms and molecules can create, consume, and transport the most vital commodity in the universe: energy. Practice calculating energy changes in reactions, explore the concept of enthalpy (the total heat content of a system), and learn how chemists use a device called a calorimeter.

 In 1840, chemist Germain Hess theorized that total heat change in a chemical reaction is equal to the sum of the heat changes of its individual steps. Study the implications of this principle, known as Hess's law. In the process, learn about heat of formation.

 Now turn to entropy, which is a measure of disorder. According to the second law of thermodynamics, the entropy of closed systems always increases. See how this change can be calculated in chemical reactions by using the absolute entropy table.

 Enthalpy and entropy are contrasting quantities. However, they are combined in the free energy equation, discovered by chemist J. Willard Gibbs, which predicts whether a reaction will take place spontaneously. Probe the difference between reactions that are endothermic (requiring heat) and exothermic (releasing heat).

 Investigate the physical properties that define the most common phases of matter: solids, liquids, and gases. Then, focus on the intermolecular forces that control which of these phases a substance occupies. Analyze the role of London dispersion forces, dipole-dipole interactions, and hydrogen bonding.

 Survey events at the molecular level when substances convert between solid, liquid, and gaseous phases. Pay particular attention to the role of temperature and pressure on these transitions. Become familiar with a powerful tool of prediction called the phase diagram.

 In the first of two lectures on the properties of gases, review the basic equations that describe their behavior. Learn the history of Boyle's law, Gay-Lussac's law, Charles's law, and Avogadro's law. Then use these four expressions to derive the celebrated ideal gas law.

 Apply the physics of moving bodies to the countless particles comprising a gas. Observe how Graham's law links the mass of gas particles to the rate at which they escape through a small aperture, a process known as effusion. See how this technique was used to enrich uranium for the first atomic weapons.

 Now turn to liquids, which have a more complicated behavior than gases. The same intermolecular forces apply to both, but at much closer range for liquids. Explore the resulting properties, including viscosity, volatility, incompressibility, and miscibility. Also consider applications of these qualities.

 Solids are characterized by a defined volume and shape, created by close packing of atoms, ions, or molecules. Focus on how packing is very regular in crystalline solids, which display lattice geometries. In particular, study the structure and properties of metals and alloys.

 Examine solids that are held together by forces other than metallic bonds. For example, sodium chloride (table salt) exhibits a lattice structure joined by ionic bonds; molecular solids such as sugar have covalent bonds; and diamond and graphite are cases of covalent network solids, as are silicates.

 Dip into the nature of solutions, distinguishing between solutes and the solvent. Review ways of reporting solution concentrations, including molarity, molality, parts per million, and parts per billion. See how chemists prepare solutions of known concentrations and also use light to determine concentration.

 Continue your investigation of solutions by probing the maximum solubility of materials in water and the concept of saturated solutions. Explore the effect of temperature on solutions. Then, watch Professor Davis demonstrate Henry's law on the solubility of gases in liquids and the phenomenon of supersaturation.

 Certain properties of solutions depend only on the concentration of the solute particles dissolved, not on the nature of the particles. Called colligative properties, these involve such behaviors as lowering the freezing point, raising the boiling point, and osmotic pressure. Study examples of each.

 Starting with a classic experiment called the elephant's toothpaste, begin your investigation of reaction rates. Learn to express rates mathematically and understand the importance of rate order, which is related to the powers of the concentrations. Extend these ideas to half-life equations, which are vital for dating geologic processes and archaeological artifacts.

 Focus on the effect of temperature on reaction rates. Learn how to use the Arrhenius equation to calculate the activation energy for a reaction, and practice solving problems. For example, why does cooling food in a refrigerator reduce the spoilage so dramatically?

 Chemical reactions often take place in a series of steps, converting starting materials into intermediates, which are then converted into products. Each stage in this process has its own associated rate law. Learn how to analyze these steps, and consider a very special class of reactants: catalysts.

 What happens when reactions can be reversed? Study reactions that take place simultaneously in both directions, leading to a dynamic equilibrium. Focus on homogeneous equilibria, which involve reactants and products in the same phase. Close with an introduction to the reaction quotient.

 Continue your study of gas-phase equilibria by investigating Le Chatelier's principle, which describes what happens when a chemical system is disturbed. Examine three different scenarios that employ this rule. Close by exploring a world-shaking application of Le Chatelier's principle.

 Now turn to acids and bases. Review the search for the defining qualities of these ubiquitous substances-a quest that eluded scientists until independent discoveries made by J. N. Bronsted and T. M. Lowry in the 1920s. Then hear how chemist Soren Sorensen devised the pH scale for measuring acidity and basicity.

 In the previous lecture, you delved into strong acids and bases-those that ionize completely in solution. In this lecture, survey weak acids and bases, zeroing in on why they only partially ionize. Practice techniques for calculating their properties and concentrations in various solutions.

 Mix things up by looking at what happens when acids and bases combine. See how a desired pH can be achieved through regulation of acid-base reactions. In the process, learn how to use the Henderson-Hasselbalch equation, which is indispensable in biology and medicine.

 So far, you have focused on acids that donate a single hydrogen ion in an acid-base reaction. Now turn to polyprotic acids-those that donate more than one proton per molecule. Investigate the complex ionization processes that ensue, and see how they play a role in regulating blood pH.

 Complete your study of acids and bases by searching out the fundamental causes of their disparate behavior. For example, why is there a difference in the ease with which various acids ionize? Your search draws on concepts from previous lectures, including electronegativity, molecular geometry, hybridization, and covalent bonding.

 Encounter reduction-oxidation (redox) reactions, which involve the exchange of electrons between substances. Discover that this process explains geological events on the early Earth, including why iron in its metallic state is so rare in nature. Then explore associated phenomena, including the activity series of metals.

 Meet three scientists who laid the foundations for electrochemistry. Robert Millikan measured the charge on the electron. Michael Faraday discovered the relationship between free energy and electrical potential. Walther Nernst formulated the relationship between redox potential and equilibrium constants. Their contributions paved the way for what came next.

 Apply your understanding of electrochemistry to one of the most influential inventions of all time: the electrical storage battery. Trace the evolution of batteries from ancient times to Alessandro Volta's pioneering voltaic cell, developed in 1800, to today's alkaline, lithium, and other innovative battery technologies.

 The energy stored in chemical bonds pales next to the energy holding atomic nuclei together. Look back to the gradual unlocking of the secrets of the nucleus, the discovery of radiation emanating from elements such as uranium, and the eventual harnessing of this phenomenon for weapons, electrical power, and medical treatments.

 Dig deeper into the nucleus to discover how so little matter can convert into the tremendous energy of a nuclear explosion, as described by Albert Einstein's famous mass-energy equation. Focus on nuclear binding energy and mass defect, both of which are connected to the release of nuclear energy.

 In the 1940s, scientists worked out techniques for speeding up the radioactivity of uranium isotopes by means of a fission chain reaction. See this process modeled with an array of mousetraps, demonstrating how the reaction can be controlled in a reactor or unleashed catastrophically in a bomb.

 Revisit the nuclear energy binding curve, noting that most elements lighter than iron can release energy by fusing together. This is an even more energetic reaction than fission, and it is what powers the sun. Follow the development of fusion weapons and the so-far-unrealized dream of fusion reactors.

 Launch into the first of three lectures on organic chemistry, which is the field dealing with carbon-based molecules, and understand why carbon makes such a versatile molecule. As an example, survey the incredible variety displayed by hydrocarbons, from bitumen (asphalt) to gasoline and methane.

 Get a taste of one of the favorite challenges for organic chemists-turning one organic compound into another. Focus on three types of reactions from the many used in organic synthesis: substitution, elimination, and addition. Close by considering the vital role of water in organic chemistry.

 Starting with the mystery of the ancient Mayan rubber ball, trace the story of polymer chemistry from lucky accidents to the advances of chemist Hermann Staudinger, who in the early 20th century showed that polymers are macromolecules. Learn how synthetic polymers are created.

 Turn from synthetic polymers to biopolymers-those that occur naturally. Focus on polysaccharides, nucleic acids, and proteins (including a special class of proteins, enzymes). Discover that living systems exercise a level of control over the synthesis of these polymers that no chemist could ever hope to achieve in the lab.

 Probe the methods used by researchers to create molecules that can correct medical problems such as inflammation, bacterial infections, and cancer. As an example, study the lock-and-key model of enzyme activity, which explains how many enzymes work, highlighting a potential weak link that can be exploited by drugs.

 Survey the types of chemicals that can harm human health. First, analyze the differences between a poison, a toxin, and a venom. Then, study examples of each, learning how arsenic disrupts ATP production, what makes nicotine deadlier than most people realize, and why venoms are typically complex proteins.

 Delve into the dark world of chemistry as a weapon of war. Crude chemical weapons were used in antiquity, but they didn't reach true sophistication and strategic significance until World War I. Profile the father of modern chemical warfare, chemist Fritz Haber, and look at the specific action of a number of deadly chemical agents.

 Explore the chemistry of fuels, which are materials that react with an oxidant to produce energy. Start with cellulose, the primary constituent of wood, then survey petroleum distillates, such as kerosene, diesel, and gasoline. Close by learning how plant oils can be used to make biodiesel, which behaves similarly to petroleum-based diesel.

 Observe what happens at the molecular level that distinguishes fuel combustion from an explosion, and also learn what constitutes a detonation, which has a precise technical meaning. Survey explosives from gunpowder to nitroglycerin to TNT to plastic explosives, and study methods of detecting explosives.

 Take a short tour of geochemistry, starting at Earth's core and working your way to the surface. Discover why our planet has a magnetic field, how radioactive atoms move continents and build mountain ranges, and why digging a hole to extract resources can produce a chemical catastrophe.

 It is said that water covers 75% of Earth's surface. But chemists know better: more accurately, Earth's surface is bathed in an aqueous solution-a mixture of water and many different dissolved solutes. Focus on dissolved carbon dioxide, methane hydrates, and the quest to extract dissolved gold.

 Now turn to the chemistry of the atmosphere, in particular the 1% composed of gases other than nitrogen and oxygen. Map the structure of the atmosphere, charting its temperature profile. Hear the good and bad news about ozone, and probe the cause of acid rain.

 Conclude the course by ranging beyond our planet to sample atoms and molecules in the cosmos. Specifically, search for two substances that are prerequisites for life: water and organic molecules. Both turn out to be plentiful, suggesting that the study of chemistry has a long and bright future!