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Transcript
Chapter 2 Elements & Atoms Dalton’s Atomic Theory • An element is composed of tiny particles called atoms. All atoms of a given element show the same chemical properties. • Atoms of different elements have different properties. • Compounds are formed when atoms of two or more elements combine. In a given compound, the relative number of atoms of each kind are definite and constant. • In an ordinary chemical reaction, no atom of any element disappears or is changed into an atom of another element. Chemical reactions involve changing the way in which the atoms are joined together. • The same elements can be combined to form different compounds by combining the elements in different proportion. Dalton predicted Law of Multiple Proportions • 1g Cu + 0.252 g O 1.252 g CuO • 1g Cu + 0.126 g O 1.126 g Cu2O Rutherford’s Experiment Rutherford’s Model of the Atom • atom is composed mainly of vacant space • all the positive charge and most of the mass is in a small area called the nucleus • electrons are in the electron cloud surrounding the nucleus Structure of the Atom • Electron e• Proton p+ • Neutron n Charge -1 +1 0 Mass 0.0005 ~1 ~1 Relative size of atom and atomic nucleus Nucleus to atom is like a pencil dot to this lecture hall Scanning Tunneling Microscope Atomic number, Z • the number of protons in the nucleus • the number of electrons in a neutral atom • the integer on the periodic table for each element Mass Number, A • the sum of the number of protons and neutrons in the nucleus • Approximately the mass of an atom Nuclear Notation X-A e.g. AX e.g. A ZX e.g. C-12 12C 12 6C An isotope has 35 electrons and 46 neutrons. The identity of this isotope is best represented as 1. 2. 20% 20% 20% 20% 20% 3. 4. 5. 1 2 3 4 5 Masses of Atoms Carbon-12 Scale Masses of the atoms are compared to the mass of C-12 isotope having a mass of 12.0000 Mass Spectrometer Atomic Masses and Isotopic Abundances natural atomic masses = sum[(atomic mass of isotope) (fractional isotopic abundance)] The average mass of the naturally occurring isotopes Cl 34.969x0.7577+36.966x0.2423=35.453amu 1. 2. 25% 25% 25% 25% 3. 4. 1 2 3 4 The Mole • a unit of measurement, quantity of matter present • Avogadro’s Number 6.022 1023 particles per mole • Latin for “pile” • 1 C-12 atom has mass 12 amu • 1 mole C-12 has mass 12 g • Avogadro’s number converts between moles and number of particles • Molar mass converts between moles and mass • You are given a 1 carat diamond, how many carbon atoms does it contain (1 carat=0.2 g) • 1 carat C x 0.2 g/1carat = 0.2 g C • 0.2 g C x 1 mol C/12.01 g C = 0.01665 mol C • 0.01665 mol C x 6.022x1023 atoms C/1 mol C =1.003x1022 C atoms Development of Periodic Table Mendeleev • 1869 - Periodic Law • allowed him to predict properties of unknown elements • the elements are arranged according to increasing atomic weights • Missing elements: 44, 68, 72, & 100 amu Predicted Properties of Ekasilicon Property Ekasilicon Germanium Atomic Weight 72 72.6 Color gray gray Density, g/mL 5.5 5.36 Oxide EsO2 GeO2 Chloride EsCl4 GeCl4 Modern Periodic Table Moseley, Henry Gwyn Jeffreys 1887–1915, English physicist. • studied the relations among spectra of different elements. • concluded that the atomic number is equal to the charge on the nucleus based on the x-ray spectra emitted by the element. • explained discrepancies in Mendeleev’s Periodic Law. Periodic Table of the Elements IA 1 1 2 3 4 5 6 7 II A III B IV B VB VI B VII B VIII B IB II B III A IV A VA VI A VII A 1 VIII A 2 H H He 1.008 1.008 3 4 5 6 7 8 9 4.0026 10 Li Be B C N O F Ne 6.939 9.0122 10.811 12.011 14.007 15.999 18.998 20.183 11 12 13 14 15 16 17 18 Na Mg Al Si P S Cl Ar 22.99 24.312 26.982 28.086 30.974 32.064 35.453 39.948 19 20 31 32 33 34 35 36 21 22 23 24 25 26 27 28 29 30 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se 39.102 40.08 44.956 47.89 50.942 51.996 54.938 55.847 58.932 58.71 63.54 65.37 69.72 72.59 74.922 78.96 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 Br 79.909 53 Kr 83.8 54 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 85.468 87.62 88.906 91.224 92.906 95.94 * 98 101.07 102.91 106.42 107.9 112.41 114.82 118.71 121.75 127.61 126.9 131.29 55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 Cs Ba **La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 132.91 137.33 138.91 178.49 180.95 183.85 186.21 190.2 192.22 195.08 196.97 200.29 204.38 207.2 208.98 * 209 * 210 * 222 87 88 89 104 105 106 107 108 109 110 111 112 Fr * 223 Ra ***Ac 226.03 227.03 Rf Ha Sg Ns Hs Mt * 261 * 262 * 263 * 262 * 265 * 268 * 269 * 272 * 277 58 59 60 61 62 63 64 65 * Designates that **Lanthanum all isotopes are Series radioactive *** Actinium Series 114 Uun Uuu Unb 116 Uuq 118 Uuh *285 *289 Based on symbols used by ACS 66 67 68 69 Uuo *293 S.M.Condren 2001 70 71 Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 140.12 140.91 144.24 * 145 150.36 151.96 157.25 158.93 162.51 164.93 167.26 168.93 173.04 174.97 90 91 92 93 94 95 96 97 98 99 100 101 102 103 Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr 232.04 231.04 238.03 237.05 * 244 * 243 * 247 * 247 * 251 * 252 * 257 * 258 * 259 * 260 Family Names Group IA alkali metals Group IIA alkaline earth metals Group VIIA halogens Group VIIIA noble gases transition metals inner transition metals • lanthanum series rare earths • actinium series trans-uranium series Diatomic Elements • H2 N2 O2 F2 Cl2 Br2 I2 Memorize • The “gens” • Hydrogen, nitrogen, oxygen, halogens • S8 and P4 No need to remember