Chemistry and Our Universe: How It All Works

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.