CHAPTER 4 STUDY GUIDEJULY 4, 2010THE DISCOVERY OF ELECTRONS cathode ray tubes – consist of two electrodes sealed in a glass tube containing a gas at very low pressure when a voltage is applied to the cathodes, a glow discharge is emitted these “rays” are emitted from cathode (- end) and travel to anode (+ end) cathode rays must be negatively charged! Millikan’s oil-drop experiment determined the charge and mass of the electronRUTHERFORD AND THE NUCLEAR ATOM Rutherford’s “Gold Foil Experiment” +-particles scattering from thin Au foils (+) conclusions: the atom is mostly empty space the atom contains a very small, dense center called the nucleus nearly all of the atom’s mass is in the nucleus the nuclear diameter is 1/10,000 to 1/100,000 times less than the atom’s radiusATOMIC NUMBER atomic number = the number of protons in the nucleus sometimes given the symbol ZAE=mass #EZ atomic # the atomic number tells you the number of protons and electrons in a neutral atom example – how many protons, neutrons, and electrons are in an Ag atom?107Ag47atomic # = 47 = # of protons AND # of electronsmass # = p+ + n  107 = 47 + n  n = 60p+ = 47, n = 60, e- = 47 example – how many protons, neutrons, and electrons are in a Ca atom?48Ca20atomic # = 20 = # of protons AND # of electronsmass # = p+ + n  48 = 20 + n  n = 28p+ = 20, n = 28, e- = 20NEUTRONS to find the number of neutrons, use the equation: mass # = # of protons + # of neutrons working with isotopes:11 n 12 n 13 n23Mg24Mg25Mg1212 121CHAPTER 4 STUDY GUIDEJULY 4, 2010MASS NUMBER AND ISOTOPES mass number = sum of protons and neutrons isotopes – atoms of the same element that contain different numbers of neutrons; have different massesand mass numbers, but they are the same element hydrogen as an example:1H 1 p+0 n 1 e-2H 1 p+1 n 1 e- oxygen as an example:16O 8 p+8 n 8 e-17O 8 p+9 n 8 e-18O 8 p+10 n 8 e-MASS SPECTROMETRY AND ISOTOPIC ABUNDANCE a mass spectrometer is used to determine atomic masses the device generates ions that pass down an evacuated path inside a magnet ions are separated based on their mass four factors determine a particle’s path in the mass spectrometer: accelerating voltage magnetic field strength masses of particles charge on particles mass spectrum of Ne+ ions (shows the masses and abundances of the isotopes of Ne)THE ATOMIC WEIGHT SCALE AND ATOMIC WEIGHTS example – calculate the number of atomic mass units in one gram.the mass of one 31P atom has been experimentally determined to be 30.99376 amuone mole of 31P atoms has a mass of 30.99376 g1.000 g(6.022 x 1023 31P atoms)(30.99376 amu)= 6.022 x 1023 amu30.99376 g 31P 1 31P atomthus, 1.00 g = 6.022 x 1023 amu the atomic weight of an element is the weighted average of the masses of its stable isotopes atomic mass (weight) = (mass #1)(% abundance) + (mass #2)(% abundance) + … etc.2CHAPTER 4 STUDY GUIDEJULY 4, 2010 example – naturally occurring Cu consists of two isotopes. it is 69.1% 63Cu with a mass of 62.9 amu and30.9% 65Cu with a mass of 64.9 amu. calculate the atomic weight of Cu to one decimal place. (convertpercent abundance to a decimal number by dividing by 100.)atomic weight = (0.691)(62.9 amu) + (0.309)(64.9 amu)atomic weight = 63.5 amu for copper example – naturally occurring chromium consists of four isotopes. it is 4.31% 2450Cr (mass = 49.946 amu),83.76% 2452Cr (mass = 51.941 amu), 9.55% 2453Cr (mass = 52.941 amu), and 2.38% 2454Cr (mass = 53.939 amu).calculate the atomic weight of chromium.atomic weight = (0.0431)(49.946 amu) + (0.8376)(51.941 amu) +(0.0955)(52.941 amu) + (0.0238)(53.939 amu)atomic weight = (2.153 + 43.506 + 5.056 + 1.284) amuatomic weight = 51.998 amu for chromium if there are only two naturally occurring isotopes of an element, and their masses are known, then thefraction of each can be calculated from the atomic weight of the element example – the atomic weight of boron is 10.811 amu. the masses of the two naturally occurring isotopes,510B and 511B, are 10.013 amu and 11.009 amu, respectively. calculate the fraction and percentage of eachisotope.x = 10B isotope abundance and 1 – x = 11B isotope abundance10.811 amu = (x)(10.013 amu) + (1 – x)(11.009 amu)10.811 amu = (10.013x + 11.009 – 11.009x) amux = 0.199 = 19.9% 10B1 – x = 0.801 = 80.1% 11BTHE PERIODIC TABLE: METALS, NON-METALS, AND METALLOIDS in 1869, Mendeleev and Meyer discovered the periodic law periodic law – the properties of the elements are periodic functions of their atomic numbers groups or families – vertical columns of elements on the periodic table periods – horizontal rows of elements on the periodic table (transition from metals to non-metals) the periodic table (the metalloids are highlighted in pink):1A 8AH 2A 3A 4A 5A 6A 7A HeLi Be B C N O F NeNa Mg 3B 4B 5B 6B 7B 8B 8B 8B 1B 2B Al Si P S Cl ArK Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br KrRb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I XeCs Ba Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At RnFr Rarep.elementstransitionmetalsrepresentativeelements the periodic table’s special groups have similar chemical and physical properties:1A 8A3CHAPTER 4 STUDY GUIDEJULY 4, 20102A 3A 4A 5A 6A 7Anoble gasesalkali metalsalkaline earthmetalsunnamedspecialshalogens3B 4B 5B 6B 7B 8B 8B 8B 1B 2Brep.elementstransitionmetalsrepresentativeelements group 1A metals – alkali metals (Li, Na, K, Rb, Cs, Fr) group 2A metals – alkaline earth metals (Be, Mg, Ca, Sr, Ba, Ra) group 6A non-metals – O, S, Se, Te group 7A non-metals – halogens (F, Cl, Br, I, At) group 8A non-metals (inert or rare) – noble gases (He, Ne, Ar, Kr, Xe, Rn) metallic character – increases right to left in a period and from top to bottom in a group less/more metallic    less metallic1A 8AH 2A 3A 4A 5A 6A 7A HeLi Be B C N O F NeNa Mg 3B 4B 5B 6B 7B 8B 8B 8B 1B 2B Al Si P S Cl ArK Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br KrRb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I XeCs Ba Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At RnFr Ra more metallic properties of metals and non-metals:properties of metals properties of non-metalsouter shells contain few electrons outer shells contain four or more electronsform cations by losing electrons form anions by gaining electronsform ionic compounds