Ch. 2 Atoms, Molecules, and ions2.1 Atomic Theory of Matter- Democritus and other Greek philosophers described indivisible particles called atomoso Plato and Aristotle established there are no indivisible particles- Dalton’s Atomic Theory (1803-1807)o Each element is composed of extremely small particles called atoms.o All atoms of a given element are identical, but the atoms of one element are different from the atoms of all other elements.o Atoms of one element cannot be changed into atoms of a diff element by chemical rxns; atoms are neither created nor destroyed in rxns. Law of conservation of mass: Total mass of materials present after chemical rxn is same as total mass present before rxn.o Cmpds are formed when atoms of more than one element combine; a given cmpd always has the same relative number and kind of atoms. Law of constant composition: In given cmpd, relative numbers and kinds of atoms are constant.- Dalton’s theory used to deduce law of multiple proportions: If two elements A and B combine toform more than one cmpd, masses of B that can combine with given mass of A are in ration of small whole numbers.2.2 The Discovery of Atomic Structure- Atoms is composed of subatomic particles. - Particles with same charge repel one another; particles with unlike charges attract.Cathode Rays and Electrons:- High voltage applied to electrodes in tube without air, causing production of radiation, which were cathode rays.- Cathode rays moved from neg. electrode to pos. electrode.- Rays detected by their causing certain materials to fluoresce, or give off light- Cathode rays deflected by electric or magnetic fields consistent with their stream of neg. electrical charge.- J. J. Thomson (1856-1940)o Cathode rays are same regardless of cathode material typeo Described them as streams of negatively charged particleso Paper is discovery of the electron. o Used the cathode-ray tube with hole in anodeo Calculated 1.76 x 108 C/g for ratio of electron’s electrical charge to its mass- Robert Millikan (1868- 1953)o Millikan oil-drop experimento Measured charge of electron: 1.602 x 10-19 Co With Thomson’s ratio, calculated electron mass as 9.10 x 10-28 g Radioactivity:- Henri Becquerel (1852- 1908)o 1896 discovered uranium spontaneously emits high-energy radiationo Radioactivity: Spontaneous emission of radiation- Ernest Rutherfordo Discovered types of radiation: alpha (α), beta (β), and gamma (γ)o Paths of α and β radiation bent by electric field in opp. directions, but γ radiation unaffectedo Showed α and β rays have fast-moving particleso α particles have 2+ charge, attracted to neg. plateo β particles have 1- charge, attracted to pos. plateo Gamma has no particles and no chargeThe Nuclear Model of the Atom:- Plum-pudding model: Thomson’s proposal that atom consists of a uniform positive sphere of matter in which mass is evenly distributed and in which electrons are embedded- 1910, Rutherford studied how α particles were deflected, or scattered, through gold foil.o Most particles passed througho Some scattering at large angleso Nuclear model: Most of mass of each atom and positive charge reside in dense region called nucleuso Empty space in atom; electrons moving around nucleuso Particles were only deflected if in contact with the small positive nucleus- Eventual discovery of positive particles, protons (by Rutherford), and neutral particles, neutrons (by Chadwick)2.3 The Modern View of Atomic Structure- Charge of electron is -1.602 x 10-19 C, and is positive for protons- Electronic charge: Quantity 1.602 x 10-19 C- Expressed in multiples, electron is 1- and proton is 1+; neutrons are neutral- All atoms have an equal number of electrons and protons, so have no net electrical