CHAPTER 4 STUDY GUIDE JULY 4 2010 THE 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 electron RUTHERFORD 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 radius ATOMIC NUMBER atomic number the number of protons in the nucleus sometimes given the symbol Z A E Z mass E atomic the atomic number tells you the number of protons and electrons in a neutral atom how many protons neutrons and electrons are in an Ag atom example 107 Ag 47 atomic 47 of protons AND of electrons mass p n 107 47 n n 60 p 47 n 60 e 47 example how many protons neutrons and electrons are in a Ca atom 48 Ca 20 atomic 20 of protons AND of electrons mass p n 48 20 n n 28 p 20 n 28 e 20 NEUTRONS to find the number of neutrons use the equation mass of protons of neutrons working with isotopes 11 n 12 n 2 3 Mg 24 Mg 2 1 2 12 13 n 5 Mg 1 2 1 CHAPTER 4 STUDY GUIDE JULY 4 2010 MASS NUMBER AND ISOTOPES mass number sum of protons and neutrons isotopes and mass numbers but they are the same element atoms of the same element that contain different numbers of neutrons have different masses hydrogen as an example 0 n 1 n 1H 1 p 2H 1 p 1 e 1 e oxygen as an example 8 e 8 e 8 e 16O 8 p 17O 8 p 18O 8 p 8 n 9 n 10 n 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 amu one mole of 31P atoms has a mass of 30 99376 g 1 000 g 6 022 x 1023 31P atoms 30 99376 amu 6 022 x 1023 amu 1 31P atom 30 99376 g 31P thus 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 2 CHAPTER 4 STUDY GUIDE JULY 4 2010 example naturally occurring Cu consists of two isotopes it is 69 1 63Cu with a mass of 62 9 amu and 30 9 65Cu with a mass of 64 9 amu calculate the atomic weight of Cu to one decimal place convert percent 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 83 76 24 calculate the atomic weight of chromium atomic weight 0 0431 49 946 amu 0 8376 51 941 amu naturally occurring chromium consists of four isotopes it is 4 31 24 53Cr mass 52 941 amu and 2 38 24 50Cr mass 49 946 amu 54Cr mass 53 939 amu 52Cr mass 51 941 amu 9 55 24 0 0955 52 941 amu 0 0238 53 939 amu atomic weight 2 153 43 506 5 056 1 284 amu atomic weight 51 998 amu for chromium if there are only two naturally occurring isotopes of an element and their masses are known then the the atomic weight of boron is 10 811 amu the masses of the two naturally occurring isotopes 11B are 10 013 amu and 11 009 amu respectively calculate the fraction and percentage of each fraction of each can be calculated from the atomic weight of the element example 10B and 5 5 isotope x 10B isotope abundance and 1 x 11B isotope abundance 10 811 amu x 10 013 amu 1 x 11 009 amu 10 811 amu 10 013x 11 009 11 009x amu x 0 199 19 9 10B 1 x 0 801 80 1 11B THE PERIODIC TABLE METALS NON METALS AND METALLOIDS in 1869 Mendeleev and Meyer discovered the periodic law periodic law groups periods the periodic table the metalloids are highlighted in pink the properties of the elements are periodic functions of their atomic numbers or families vertical columns of elements on the periodic table horizontal rows of elements on the periodic table transition from metals to non metals 3B Sc Y 4B Ti Zr Hf 6B 7B 5B Cr Mn V Tc Nb Mo Ta W Re 8B Fe Ru Os 8B Co Rh Ir 8B Ni Pd Pt 1B Cu Ag Au 2B Zn Cd Hg transition metals 3A B Al Ga In Tl 4A C Si Ge Sn Pb 5A N P As Sb Bi 6A O S Se Te Po 7A F Cl Br I At representative elements 1A 2A H Be Li Na Mg Ca K Sr Rb Ba Cs Ra Fr rep elements 1A the periodic table s special groups have similar chemical and physical properties 3 8A He Ne Ar Kr Xe Rn 8A 2A h t r a e e n i l a k l a s l a t e m s l a t e m i l a k l a rep elements CHAPTER 4 STUDY GUIDE JULY 4 2010 3B 4B 5B 6B 7B 8B 8B 8B 1B 2B 3A 4A 5A 6A 7A d e m a n n u s l a i c e p s s n e g o a h l s e s a g e b o n l transition metals representative elements 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 1A H 2A Be Li Na Mg Ca K Sr Rb Ba Cs Fr Ra more metallic 3B Sc Y 4B Ti Zr Hf …