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Chemistry 6A Fall 2007 Chem. 6A This week: Dr. J. A. Mack CSUS Chem 6A F07 Dr. Mack 1 It’s time to play… 9-17-07 Experiment Lecture: Chapter 2 2 (You will need goggles!!) No goggles, no lab! No open toed shoes allowed! No pre-lab, no lab! No excuses! 9/17/07 9-17-07 Lab: 9-17-07 CSUS Chem 6A F07 Dr. Mack 2 It’s time to play… Cs cesium MgCl2 magnesium chloride Hg Mercury CuSO4 copper (II) sulfate Zn zinc calcium acetate Ca(C2H3O2)2 As Arsenic hydrogen hydroxide CSUS Chem 6A F07 Dr. Mack 5 9-17-07 CSUS Chem 6A F07 Dr. Mack HOH or water… H2O 6 1 The modern periodic table is defined by: 1 Groups (families) (columns down) The Periods are labeled: 2 3 Periods (rows across) 9-17-07 CSUS Chem 6A F07 Dr. Mack 7 9-17-07 CSUS Chem 6A F07 Dr. Mack 8 The Groups are labeled: 1A 7A 8A 2A 3A 4A 5A 6A 3B 4B 5B 6B 7B The “A” refers to the “main group elements” 8B 1B 2B The “B” refers to the transition metal elements. Tin is in group 4A (14) in the 5th period. 9-17-07 CSUS Chem 6A F07 Dr. Mack 9 9-17-07 CSUS Chem 6A F07 Dr. Mack 11 2 Periodic Table: Metallic Periodic Table: Metallic arrangement arrangement 1 IA 1 18 VIIIA 2 IIA 13 IIIA 14 IVA 15 VA 16 VIA 17 VIIA 1 IA 1 2 18 VIIIA 2 IIA 13 IIIA 14 IVA 15 VA 16 VIA 17 VIIA 2 3 IIIB 3 4 4 IVB 5 VB 6 VIB 7 VIIB 8 9 VIIIB 10 11 IB 12 IIB Nonmetals Metals 5 6 7 7 12 9-17-07 Today’s Periodic table 6 VIB 7 VIIB 8 9 VIIIB 10 11 IB 12 IIB CSUS Chem 6A F07 Dr. Mack Metalloids 13 Today’s Periodic table Group 1A elements are also know as the “Alkali Metals” as they form basic salts 9-17-07 5 VB somewhere in between metals and non-metals 5 CSUS Chem 6A F07 Dr. Mack 4 IVB 4 6 9-17-07 3 IIIB 3 CSUS Chem 6A F07 Dr. Mack 14 Group 2A elements are also know as the “Alkaline earth Metals” as they are only found in the ground as metal salts (carbonates) 9-17-07 CSUS Chem 6A F07 Dr. Mack 15 3 Today’s Periodic table Today’s Periodic table Group 2B – 8B elements are also know as the “Transition Metals”. Metals” They may be found in the earth as pure metals or as ores (salts). 9-17-07 CSUS Chem 6A F07 Dr. Mack Group 7A elements are also know as the “Halogens”. They form acids with hydrogen and exist as diatomic molecules. (F2, Cl2…) 16 9-17-07 Today’s Periodic table CSUS Chem 6A F07 Dr. Mack 17 The discovery of modern atomic structure: Group 8A elements are also know as the “Noble gasses”. They are inert to reaction for the most part. He is found underground! 9-17-07 CSUS Chem 6A F07 Dr. Mack Experiments! 18 9-17-07 CSUS Chem 6A F07 Dr. Mack 19 4 Rutherford’s Scattering Experiment: 1911 Rutherford’s Experiment: Explained •Most of the α-particles passed through the gold foil. •Some α-particles were deflected slightly as they came close to the nucleus by the + charge repulsion. •Some were deflect backwards by direct collisions with the nucleus. Conclusion: •Atoms are mostly space. •The nucleus caries most of the mass with a positive charge. 9-17-07 CSUS Chem 6A F07 Dr. Mack 20 The Composition of an Atom: 9-17-07 CSUS Chem 6A F07 Dr. Mack 21 Further experiments lead to the discovery and characterization of the electron, proton and neutron. Electron: -1 charge The atom is mostly empty space J.J. Thompson cathode ray tube (1897) electrons were negatively charged R. Millkan Oil drop experiment (1909) charge on the electron Proton: +1 charge •protons and neutrons in the nucleus. •the number of electrons is equal to the number of protons. Neutron: no charge E. Rutherford (1918) hydrogen nucleus termed a “proton” J. Chadwick (1932) neutral particle with the mass of a proton •electrons in space around the nucleus. 9-17-07 CSUS Chem 6A F07 Dr. Mack 23 9-17-07 CSUS Chem 6A F07 Dr. Mack 24 5 Atomic Number, Z Isotopes, Atomic Numbers, and Mass Numbers •Atomic number (Z) = number of protons in the nucleus. An element’s identity is defined by the number of protons in the nucleus: Z •Mass number (A) = total number of nucleons in the nucleus (i.e., protons and neutrons). •One nucleon has a mass of 1 amu (Atomic Atomic Mass Unit) Dalton” Unit a.k.a “Dalton Atomic number 13 •Isotopes have the same Z but different A. Atom symbol Al •The elements are arranged by Z on the periodic table. Atomic weight 26.981 By convention, for element X, we write 9-17-07 CSUS Chem 6A F07 Dr. Mack 25 75 The isotope 34 Se is used medically for diagnosis of 75 34 Se have? 26 These isotopes occur in proportions represented by their natural abundances. 75 34 Se As macroscopic beings, we measure matter on a “bulk” scale (many atoms). 34 protons electrons = 34 The fraction or abundance of each of the individual isotopes statistically weights the average atomic mass of an element. neutrons = 75-34 = 41 9-17-07 CSUS Chem 6A F07 Dr. Mack In nature, an element is found to contain a mixture of all of the naturally occurring isotopes. 75 protons + neutrons protons = 34 X Atomic Masses and the Periodic Table: pancreatic disorders. How many protons, neutrons, and electrons does an atom of 9-17-07 A Z CSUS Chem 6A F07 Dr. Mack 27 9-17-07 CSUS Chem 6A F07 Dr. Mack 28 6 Example: most The sum of the intensities adds up to 100%. Chlorine has two isotopes: The relative Cl-35 abundance of each 35 17 isotope is indicated by the height of the least line corresponding & Cl- 37 37 17 Cl shorthand notation Cl Each isotope occurs in nature with a specific mass and corresponding fraction or “Percent Abundance”. 35 17 to a particular mass. 75.53 % 37 17 Cl 34.96885 u 24.47 % Cl 36.96590 u 1 u = 1 amu 9-17-07 CSUS Chem 6A F07 Dr. Mack 29 fraction that are Cl-35 mass of a Cl-35 atom m Cl (u) = m Cl-35 × abundance of Cl-35 mass of a Cl-37 atom + m Cl-37 × CSUS Chem 6A F07 Dr. Mack 30 Avogadro’s Number and the Mole The average weighted atomic mass is determined by the following mathematical expression: Average mass of a Cl atom 9-17-07 The concept of a mole is defined so that we may equate the amount of matter (mass) to the number of particles (mole). fraction that are Cl-37 The Standard is based upon the C-12 isotope. abundance of Cl-37 The atomic mass of 12C is defined as exactly 12 u. = 34.96885u × 0.7553 + 36.96590 × 0.2447 = 35.45 u The atomic mass of 12C is 1.99265 × 10-23 g. (4 sig. fig) 1 amu = (the mass of one 12C atom ÷12) = 1.66054 × 10-24g = 1.66054 × 10-27 kg This is the value that is reported on the periodic table. Note that: 0.7553 + 0.2447 = 1.0000 (100%) 9-17-07 CSUS Chem 6A F07 Dr. Mack 31 9-17-07 CSUS Chem 6A F07 Dr. Mack 32 7 Molar Masses Avagagro’s Number Since we can equate mass (how much matter) with moles 12C Since one mole of has a mass of 12g (exactly), 12g of contains 6.022142 x 1023 12C-atoms. (how many particles) we now have a conversion that relates the two. 12C But carbon exists as 3 isotopes: C-12, C-13 &C-14 mols The average atomic mass of carbon is 12.011 u. 9-17-07 aka: Avogadro's number (NA) Yes, since NA is so large, the statistics hold. CSUS Chem 6A F07 Dr. Mack molar mass (g/mol) = grams The Molar Mass of a substance is the amount of matter that contains one-mole or 6.022 × 1023 particles. From this we conclude that 12.011g of carbon contains 6.022142 x 1023 C-atoms Is this a valid assumption? × factor The atomic masses on the Periodic Table also represent the molar masses of each element in grams per mole (g/mol) 33 9-17-07 CSUS Chem 6A F07 Dr. Mack 34 So if you have 12.011g of carbon… you have 6.022×1023 carbon atoms! So if you have 39.95g of argon… you have 6.022×1023 argon atoms! if you have a mole of dollar bills… you are Bill Gates… you have 6.022×1023 bucks! and if you have 6.022×1023 avocados… you have… 9-17-07 a “guacamole” CSUS Chem 6A F07 Dr. Mack 36 8