Freshman Chemistry (20A)Chemistry and the Periodic TableMolecular Units, Moles, and the Periodic TableMass VolumeSignificant Figures, Calculators, and Wrong AnswersUnits, Units Systems, and AlgebraDensitiesAvogadro’s Hypothesis on gasesThe structure of the AtomRecall that we defined 1 mole of C atoms as weighing 12 grams. Let’s check this definition by looking at the periodic table under C. Wait! We see that the mass of carbon is listed as 12.011 g/mol, not 12.000 g/mol! Did we screw up? Well, let’s consiParticle mass chargeElectron me = 9.11 x 10-31 kg = 5.49x10-4u -1.6 x 10-19 CoulombsSignificant Figures (again) Since we know how Avogadro’s number is defined, let’s imagine an experiment in which we had a pretty sensitive balance that could measure the weight of a certain amount of 12C to the nearest thousandth of gram (the nearest milAtomic StructureIonic and Covalent Bonding – Mostly ionic, and part of Chapter 13Before we move on to the details relating the electronic structure of atoms, let’s finish up our chemistry review by discussing the various types of chemical bonds. Once again, consider the reactionIn an ionic molecule, two (or more) counterions are held together by Coulombic forces – which means forces that are related to interacting charges. If we consider bringing two oppositely charged ions together, then one can imagine that they will attractOptional problem #1 – really good one to work outEND CHAPTER 1,2 LECTURESTerms and Other Stuff from This series of LecturesFreshman Chemistry (20A)Lecture Series #1Chemistry and the Periodic TableThe point of this course is to learn how to think about chemical structure, the periodic table, andthe relevance of these things to the world around us.Consider the periodic table. The elements at the far right are essentially inert. The elements atthe far left are amongst the most reactive of all elements. Yet the difference between the twoelements is that the ones on the far right are characterized by 1 less electron and 1 less protonthan the corresponding element, 1 row down, on the far left. If you don’t know what an electronor a proton is, just wait a bit. We’ll get to that.Let’s take one of the simplest reactions possible2Na + Br2  2NaBrThere are several things to note about this reactionFirst, Na is a covalent solid, and it is a metal – which means that it is very shiny, like a silveredmirror. In fact, in terms of its electrical conductivity, it is one of the best metals there is. Recallalso that, by nature of its position at the far left of the periodic table, it is a very reactive element.Br2 is a molecule, and it is a liquid until 58oC, above which it is a gas, and it is red in color. Itturns out that Br2 is only slightly reactive, on a relative scale that would compare the reactivity ofvarious elemental molecules.NaBr is an ionic solid – which implies that it is not a metal, but rather an insulator. In fact, it isone of the best insulators that there is. In addition, it is nearly completely inert, or non-reactive,and it is clear and colorless.So, we combine a highly reactive covalent metallic solid, with a quasi-reactive red liquid or gas,and we get an inert product that is an ionic, insulating clear colorless solid.Let’s look at another reaction:Na + H2O  NaOH + ½ H2In this reaction, we are taking a reactive, metallic, shiny, covalent solid and reacting it with aclear, colorless molecular liquid (how is the liquid held together?) and producing a colorless,white reactive ionic solid and a slightly reactive, colorless, molecular gas.We have only written down two apparently simple (and common) chemical reactions, and wehave already introduced a tremendous amount of complexity. Other questions that we haven’tbrought up yet include: How fast are these reactions? Do they proceed to completion? etc.With this complexity already introduced, how can we ever hope to understand truly complicatedchemical systems, such as living organisms, or the earth’s atmosphere, or the chemical processesthat are involved in fabricating electronics or plastics, etc.? In this class, we will only begin toshed light on these issues, and we will do it slowly, one step at a time. We will first introducethe language of chemistry, and we will follow this with a highly simplified description of whatmakes up an atom. This description will necessarily involve some quantum mechanics (startingwith Chapter 15). We will discuss the types of experiments that have led to various descriptionsof chemistry, including spectroscopy, which is the interaction of light with matter. After wediscuss the atom, we will move onto the structure of simple molecules, and how simple modelsmay be used (with caution!) to predict such structures. Finally, we will increase the complexityof the systems we are trying to describe, and include organic molecules, polymers, and transitionmetal complexes (although we may not quite get to the transition metals).For now, let’s back up a bit, and just try to understand the language of the reactions we havealready mentioned, and discuss why they were written they way they were.First, let’s return to the reaction:2Na + Br2  2NaBrWhat we are saying when we write this reaction down is that 2 units of sodium atoms react with1 unit of bromine gas to produce two units of sodiumbromide. The numbers in front of thechemical species are intended to balance the chemical reaction.We could have just as easily written the reaction asNa + ½ Br2 NaBrNotice that this works out just as well, if we are trying to conserve mass. In fact, that is just whatwe are trying to do when we balance a chemical equation. In all chemical reactions, mass isconserved. This is a principle that was first stated by Lavoisier early in the last century.Notice that we did something similar when we wrote down our second reaction of the dayNa + H2O  NaOH + ½ H2However, this reaction is a little more complicated – 2 reactants to produce 2 products.Balancing equations never involves more than algebra, but, nevertheless, the algebra can get alittle complicated.Molecular Units, Moles, and the Periodic TableWhen we say that 1 unit of sodium plus 1 unit of water reacts, what do we mean by units?Chemists use all types of units to describe quantities of chemicals. Below, we have listed a few:Mass VolumeGrams (g) liters (l) = 0.2 gallons (roughly)milligrams (mg) = 0.001 g) milliliter (ml) = 0.001