1 FUNDAMENTAL LAWS OF CHEMISTRY Lavoisier s Fundamental Laws of Chemistry Father of Modern Chemistry Late 18th century French aristocrat Guillotined during the French Revolution 1 Law of Mass Conservation In any chemical processes matter cannot be created or destroyed 2 Law of Definite Composition A chemical compound always has the same mass composition regardless of its source Dalton s Atomic Theory Early 19th century British scientist 1 All matter is made of indivisible atoms 2 Elements are made of one type of atom All atoms have the same chemical and physical properties mostly 3 Compounds are made of atoms in fixed proportions Can t use of an atom to make a compound Also stated as Law of Multiple Proportions 4 Atoms change arrangement in a chemical reaction not identity Law of Multiple Proportions When two elements combine to form two or more compounds the ratio formed from each compound s mass ratio always yields a fraction In other words elements cannot combine together with random compositions The number of atoms of each element in a compound must be a whole number 2 Example Consider two compounds of sulfur and oxygen Compound A has a mass composition of 49 9 oxygen and 50 1 sulfur Compound B has a mass composition of 59 9 oxygen and 40 1 sulfur The oxygen to sulfur ratio for compound A is 49 9 0 9960 50 1 The oxygen to sulfur ratio for compound B is 59 9 1 494 40 1 The law of multiple proportions says that a ratio of these ratios must yield a simple fraction 0 9960 2 0 6667 1 494 3 Compound A has two thirds the oxygen that compound B has Modern analysis yields that compound A SO2 and compound B SO3 3 ATOMIC STRUCTURE HISTORY 1897 J J Thomson Discovered cathode rays Cathode rays were soon interpreted as beams of electrons Thomson measured how the electrons were deflected by a magnetic field and calculated the charge to mass ratio e m Thomson used his findings to construct the plum pudding model of the atom Won Nobel Prize in 1906 1909 Robert Milliken Milliken found that tiny drops of oil charged with static electricity had only discrete values of charge based on their deflection by an electric field Milliken measured the fundamental unit of charge to be 1 6 10 19 Coulombs Based on Thomson s experiments he also measured the mass of the electron to be 9 10 31 kilograms Won Nobel Prize in 1923 1910 Ernest Rutherford Aimed a beam of alpha particles 4He nuclei at a thin gold sheet Most particles went right through the sheet a little surprising Some particles deflected backwards very surprising Rutherford said It was almost as incredible as if you fired a 15 inch shell at a piece of tissue paper and it came back and hit you Results were interpreted as the atom having a very small yet very heavy nucleus Won Nobel Prize in 1908 4 ATOMIC STRUCTURE Two components of an atom Nucleus pl nuclei composite particle size 10 15 m 10 5 positively charged SI units multiples of 1 609 x 10 19 C atomic units 1 2 3 116 mass varies from 1 7 x 10 27 to 5 x 10 25 kg 1 amu to 293 amu contains almost all the mass of an atom occupies very small volume in the atom Electrons e fundamental particle of nature size unknown r 10 18 m negatively charged SI units 1 609 x 10 19 C atomic units 1 mass SI units 9 109 x 10 31 kg atomic units 5 486 x 10 4 amu movement of electron occupies the size of the atom 1 10 10 m Definition 1 Angstrom 10 10 m NUCLEAR STRUCTURE Two components of nucleus Proton p size 10 15 m 10 5 charge 1 atomic units mass 1 673 x 10 27 kg 1 0073 amu number of p defines element Neutron n size 10 15 m 10 5 same as proton charge 0 atomic units mass 1 675 x 10 27 kg 1 0087 amu number of n defines isotope of element ATOMIC STRUCTURE HISTORY continued 1932 James Chadwick Showed that atoms have a third particle different than the electron and proton Aimed a beam of alpha particles 4He nuclei at a sheet of beryllium to produce uncharged particles Interacting these uncharged particles with other nuclei showed that they must have approximately the same mass as a proton Won Nobel Prize in 1935 5 A ATOMIC SYMBOLS Z Sy Atomic Number Z number of protons in an atom subscript before elemental symbol Mass Number A number of protons and neutrons in an atom superscript before elemental symbol mass number approximates how heavy the atom is in atomic mass units Examples Oxygen 16 has 8 p and 8 n element oxygen of p 8 of n 9 mass 17 oxygen 8 10 18 carbon 6 6 12 carbon 6 8 14 lead 82 126 208 symbol 17 8 18 8 O 12 6 14 6 C 208 82 Pb O C Definition isotope an atom with the same atomic number as another atom but a different mass number i e isotopes have the same number of protons but a different number of neutrons isotopes have the same chemical properties Notes oxygen 16 and oxygen 18 are isotopes of oxygen carbon 12 and carbon 14 are isotopes of carbon nuclide refers to specific nucleus often used interchangeably with isotope DEFINITION OF ATOMIC MASS UNIT Mass of 12C is 12 000000 amu BY DEFINITION 1 amu 1 66 x 10 27 kg amu also abbreviated as u 1 amu 1 u For atomic masses amu is much more convenient unit than kilograms m 1H 1 6737 x 10 27 kg 1 0079 amu m 14N 2 3253 x 10 26 kg 14 004 amu m 56Fe 9 2882 x 10 26 kg 55 935 amu 6 ATOMIC AND MOLECULAR MASSES Average Atomic Mass also Atomic Weight If element has more than one naturally occurring isotope atomic mass is an average of the mass of the isotopes Average is performed accounting for the relative natural abundance of each isotope Example Copper nuclide abundance 63 Cu 69 17 65 Cu 30 83 mass amu 62 940 64 928 m Cu 0 6917 62 940 amu 0 3083 64 928 amu 63 55 amu Example Neon nuclide 20 Ne 21 Ne 22 Ne abundance mass amu 90 48 19 992 0 27 20 994 9 25 21 991 m Ne 0 9048 19 992 amu 0 0027 20 994 amu 0 0925 21 991 amu 20 18 amu PERIODIC TABLE OF GROUPS OF ELEMENTS Two different classification schemes Metal Nonmetal Scheme based on physical properties Metals characteristics of metals luster shine high electrical conductivity high heat conductivity Ions are generally positively charged Elements on left side of periodic table are metals Nonmetals characteristics of nonmetals poor electrical conductivity insulator poor heat conductivity insulator Ions are generally negatively charged Elements in the upper right corner of table are nonmetals Metalloids in between metal and nonmetal B Si Ge As Sb Te At 7 …