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 charge- Most atom diameters are between 1 x 10-10 m (100 pm) and 5 x 10-10 m (500pm), or 1-5 Å- Angstrom (Å): SI unit of length for atomic dimensionso 1 Å= 1 x 10-10 m- Electrons attracted to protons of nucleus by electrostatic force between particles of opp. electrical charge- Atomic mass unit (amu): 1 amu= 1.66054 x 10-24 g- Diameter of atomic nucleus: 10-4 ÅAtomic Numbers, Mass Numbers, and Isotopes:- Atoms of each element have characteristic number of protons.- Atomic number: Number of protons of element- Mass number: Number of protons plus neutrons in atom- Isotopes: Atoms with identical atomic numbers, but different mass numbers (same protons different neutrons)2.4 Atomic WeightsThe Atomic Mass Scale:- Hydrogen, lightest atom, arbitrarily assigned relative mass of 1--12C has exactly 12 amu.Atomic Weight:- Atomic weight: Average atomic mass of element-The Mass Spectrometer:- Mass spectrometer: Most accurate means of determining atomic weights- Mass spectrum: Gives masses of ions and relative abundances2.5 The Periodic Table- Periodic table: The arrangement of elements in order of increasing atomic number, with elements having similar properties placed in vertical columns- Periods: Horizontal rows of periodic tableso First has just H and Heo 7 periods- Groups: Vertical columnso 1-18o Elements in group have similarities in physical and chemical properties.o Alkali metals (1), alkaline earth metals (2), chalcogens (16), halogens (17), noble gases (or rare gases, 18)o Metallic elements/ metals: Left and middle of periodic table; luster, high electrical and heat conductivity, solid at room temp (except Hg)o Nonmetallic elements/ nonmetals: Separated from metals by line from B to At; varying state of mattero Metalloids: Elements with properties of metals and nonmetals2.6 Molecules and Molecular Compounds- Only noble gases are normally found as isolated atoms- Most matter is composed of molecules or ions.Molecules and Chemical Formulas:- Many elements found in molecular form- two or more of same type of atom bonded together- Chemical formula: Ex. O2- Diatomic molecule: Molecule made up of two atomso H, O, N, F, Cl, Br, and I elements form diatomic molecules- Oxygen (O2) and ozone (O3) exhibit different chemical and physical properties.- Molecular compounds: Compounds composed of molecules, containing more than one type of atom- Most molecular substances contain only nonmetals.Molecular and Empirical Formulas:- Molecular formulas: Chemical formulas that indicate the actual numbers of atoms in a molecule- Empirical formulas: Chemical formulas that give only the relative number of atoms of each type in a moleculeo Subscripts are always smallest possible whole-number ratios- Ex. H2O2 can be