CHEM 1211K 1st Edition Lecture 4 Outline of Last Lecture I. Chapter 1 Matter, Measurement, and Problem Solving ReviewChapter 2 Atoms and ElementsII. Modern Atomic TheoryA. Law of Conservation of Mass (by Antoine Lavoisier) In a chemical reaction, matter is neither created nor destroyed Total mass of reactants = Total mass of products B. Dalton proposed a theory of matter based on it having ultimate, indivisible particles toexplain these laws.1. Each element is composed of tiny, indestructible particles called atoms2. All atoms of a given element have the same mass and other properties that distinguish them from atoms of other elements (the atom for each element is unique)3. Atoms combine in simple, whole-number ratios to form molecules of compounds4. In a chemical reaction, atoms of one element cannot change into atoms of another elementIII. 2.4 The Discovery of the Electron2.4.1 Electrical ChargesTwo kinds of charge called + and –Opposite charges attract+ attracted to –Like charges repel+ repels +– repels –To be neutral, something must have no charge or equal amounts of opposite charges2.4.2 Cathode Rays•Glass tube containing metal electrodes from which almost all the air has been evacuatedThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.•When connected to a high voltage power supply, a glowing area is seen emanating fromthe cathode.IV. 2.5 The Structure of the AtomA. The structure of the atom contains many negatively charged electronsB. These electrons are held in the atom by their attraction for a positively charged electric field within the atom.- there had to be a source of positive charge because the atom is neutral- Thomson assumed there were no positively charged pieces because none showed up in the cathode ray experiment.V. Rutherford’s Nuclear Model1. The atom contains a tiny dense center called the nucleusa. the amount of space taken by the nucleus is only about 1/10 trillionth the volume of the atom2. The nucleus has essentially the entire mass of the atom the electrons weigh so little they give practically no mass to the atom3. The nucleus is positively charged  the amount of positive charge balances the negative charge of the electrons4. The electrons are dispersed in the empty space of the atom surrounding the nucleusCurrent