Lecture Presentation Chapter 2 Atoms Molecules and Ions 2012 Pearson Education Inc John D Bookstaver St Charles Community College Cottleville MO Atomic Theory of Matter The theory that atoms are the fundamental building blocks of matter reemerged in the early nineteenth century championed by John Dalton 2012 Pearson Education Inc Atoms Molecules and Ions Dalton s Postulates Each element is composed of extremely small particles called atoms 2012 Pearson Education Inc Atoms Molecules and Ions Dalton s Postulates All atoms of a given element are identical to one another in mass and other properties but the atoms of one element are different from the atoms of all other elements 2012 Pearson Education Inc Atoms Molecules and Ions Dalton s Postulates Atoms of an element are not changed into atoms of a different element by chemical reactions atoms are neither created nor destroyed in chemical reactions 2012 Pearson Education Inc Atoms Molecules and Ions Dalton s Postulates Compounds are formed when atoms of more than one element combine a given compound always has the same relative number and kind of atoms 2012 Pearson Education Inc Atoms Molecules and Ions Law of Conservation of Mass The total mass of substances present at the end of a chemical process is the same as the mass of substances present before the process took place 2012 Pearson Education Inc Atoms Molecules and Ions The Electron Streams of negatively charged particles were found to emanate from cathode tubes causing fluorescence J J Thomson is credited with their discovery 1897 2012 Pearson Education Inc Atoms Molecules and Ions The Electron Thomson measured the charge mass ratio of the electron to be 1 76 108 coulombs gram C g 2012 Pearson Education Inc Atoms Molecules and Ions Millikan Oil Drop Experiment Once the charge mass ratio of the electron was known determination of either the charge or the mass of an electron would yield the other 2012 Pearson Education Inc Atoms Molecules and Ions Millikan Oil Drop Experiment Robert Millikan University of Chicago determined the charge on the electron in 1909 2012 Pearson Education Inc Atoms Molecules and Ions Radioactivity Radioactivity is the spontaneous emission of radiation by an atom It was first observed by Henri Becquerel Marie and Pierre Curie also studied it 2012 Pearson Education Inc Atoms Molecules and Ions Radioactivity Three types of radiation were discovered by Ernest Rutherford particles particles rays 2012 Pearson Education Inc Atoms Molecules and Ions The Atom circa 1900 The prevailing theory was that of the plum pudding model put forward by Thomson It featured a positive sphere of matter with negative electrons imbedded in it 2012 Pearson Education Inc Atoms Molecules and Ions Discovery of the Nucleus Ernest Rutherford shot particles at a thin sheet of gold foil and observed the pattern of scatter of the particles 2012 Pearson Education Inc Atoms Molecules and Ions The Nuclear Atom Since some particles were deflected at large angles Thomson s model could not be correct 2012 Pearson Education Inc Atoms Molecules and Ions The Nuclear Atom Rutherford postulated a very small dense nucleus with the electrons around the outside of the atom Most of the volume of the atom is empty space 2012 Pearson Education Inc Atoms Molecules and Ions Other Subatomic Particles Protons were discovered by Rutherford in 1919 Neutrons were discovered by James Chadwick in 1932 2012 Pearson Education Inc Atoms Molecules and Ions Subatomic Particles Protons and electrons are the only particles that Protons and neutrons have essentially the same have a charge mass The mass of an electron is so small we ignore it 2012 Pearson Education Inc Atoms Molecules and Ions Symbols of Elements Elements are symbolized by one or two letters 2012 Pearson Education Inc Atoms Molecules and Ions Symbols of Elements All atoms of the same element have the same number of protons which is called the atomic number Z 2012 Pearson Education Inc Atoms Molecules and Ions Symbols of Elements The mass of an atom in atomic mass units amu is the total number of protons and neutrons in the atom 2012 Pearson Education Inc Atoms Molecules and Ions Isotopes Isotopes are atoms of the same element with different masses Isotopes have different numbers of neutrons 2012 Pearson Education Inc Atoms Molecules and Ions Atomic Mass Atomic and molecular masses can be measured with great accuracy using a mass spectrometer 2012 Pearson Education Inc Atoms Molecules and Ions Average Mass Because in the real world we use large amounts of atoms and molecules we use average masses in calculations Average mass is calculated from the isotopes of an element weighted by their relative abundances 2012 Pearson Education Inc Atoms Molecules and Ions Periodic Table The periodic table is a systematic catalog of the elements Elements are arranged in order of atomic number 2012 Pearson Education Inc Atoms Molecules and Ions Periodic Table The rows on the periodic chart are periods Columns are groups Elements in the same group have similar chemical properties 2012 Pearson Education Inc Atoms Molecules and Ions Periodicity When one looks at the chemical properties of elements one notices a repeating pattern of reactivities 2012 Pearson Education Inc Atoms Molecules and Ions Groups These five groups are known by their names 2012 Pearson Education Inc Atoms Molecules and Ions Periodic Table Nonmetals are on the right side of the periodic table with the exception of H 2012 Pearson Education Inc Atoms Molecules and Ions Periodic Table Metalloids border the stair step line with the exception of Al Po and At 2012 Pearson Education Inc Atoms Molecules and Ions Periodic Table Metals are on the left side of the chart 2012 Pearson Education Inc Atoms Molecules and Ions Chemical Formulas The subscript to the right of the symbol of an element tells the number of atoms of that element in one molecule of the compound 2012 Pearson Education Inc Atoms Molecules and Ions Chemical Formulas Molecular compounds are composed of molecules and almost always contain only nonmetals 2012 Pearson Education Inc Atoms Molecules and Ions Diatomic Molecules These seven elements occur naturally as molecules containing two atoms Hydrogen Nitrogen Oxygen Fluorine Chlorine Bromine Iodine 2012 Pearson Education Inc Atoms Molecules and Ions Types of Formulas Empirical formulas give the lowest whole number ratio of atoms of each element in a compound Molecular formulas give the exact