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Chem 105 John Keller Mon. 9-16-09 Today Isotope practice problem Periodic Table Cations Anions Mon 9-16-09 Announcements Please EMAIL any new or changed clicker serial numbers to [email protected]. Please use the HALLWAY KIOSK outside of 194 Reichardt 24x7 to check your clicker function and registration. 1 Mon 9-16-09 36% 23% 14% 8% 7% 2 1% 7 5 4 3 2% 6 8% 2 This is the Participant Number chart for KELLER MWF 2:15-3:15. If you click your clicker here, and it is registered in the database on this computer, it should also light up in class. No Yes No 2 3 4 5 6 7 Ye s 1. 2. 3. 4. 5. 6. 7. 8. Isotope % practice problem from OWL Mon 9-16-09 3 The element lithium has an atomic weight of 6.94 and consists of two stable isotopes lithium-7 and lithium-6. The isotope lithium-7 has an atomic mass of 7.02 amu and a percent natural abundance of 92.6%. The isotope lithium-6 has a percent natural abundance of 7.42%. What is the atomic mass of lithium-6? ____________amu One interpretation of this phrase is: “A mole of lithium atoms (from nature) has a mass of 6.94 g.” Mon 9-16-09 4 A natural lithium atom has a mass of 6.94 amu. 1. True 2. False 73 Mon 9-16-09 ls e Fa Tr ue 45 5 A natural lithium atom has a mass of 6.94 amu. 1. True 2. False 6.94 g is the mass of a mole of natural lithium, which contains about 93% of Li-7 and about 7% of Li-6 atoms. There is no such thing as a “natural lithium atom”. No particle has a mass of 6.94 amu. Mon 9-16-09 6 The element lithium has an atomic weight of 6.94 and consists of two stable isotopes lithium-7 and lithium-6. The isotope lithium-7 has an atomic mass of 7.02 amu and a percent natural abundance of 92.6%. The isotope lithium-6 has a percent natural abundance of 7.42%. What is the atomic mass of lithium-6? Mon 9-16-09 ____________amu 7 Fraction 7Li = % 7Li ÷ 100 = 0.926 moles 7Li/mole nat Li Fraction 6Li = % 6Li ÷ 100 = 0.0742 moles 6Li/mole nat Li Mass of 7Li/ mol nat Li + mass 6Li/ mol nat Li = 6.94 g/mol nat Li 7.02 g x 6 = 6.94 g × + × 0.926 mol Li 0.0742 mol Li 7 6 mol Li mol Li 7 Or 0.926 mol 7Li 7.02 g 0.0742 mol 6Li x 6.94 g × + = mol nat Li mol 7Li mol nat Li mol 6Li mol nat Li 0.926 * 7.02 = 6.50052 The product of 0.926 and 7.02 has 3 sig figs. (underlined). When you subtract that number from 6.94, the answer has the last significant 6.94000 decimal in the “hundredths” column. So even − 6.50052 though both addends have 3 sig figs, the 0.43948 answer has only 2. This often happens when two numbers that are close in value are subtracted – you lose information! Then in the 0.43948 = 5.9229 g = 5.9 g last division, the 2-sig-fig numerator requires 0.0742 that the answer also have 2-sig figs. Mon 9-16-09 0.926(7.02) g + 0.0742 x = 6.94 g 6.94 − 0.926(7.02) g 0.0742 x = 5.923 g = 5.9 g x= 8 Periodic Table Mon 9-16-09 9 Periodic Table of the Elements 1) See www.webelements.com 2) Tom Lehrer 3) Periodic table http://www.privatehand.com/flash/elements.html Mon 9-16-09 10 “American system” of numbering groups 1A 2A Non-metals (incl H) 3B 4B 5B 6B 7B ----8B----- 1B 2B 3A 4A 5A 6A 7A 8A metalloids metals Inert gases See wall periodic tables Mon 9-16-09 11 FAQ: In Chem 105, do I have to memorize the names and formulas of the elements? Yes, some of them, as shown below. Exams will contain a periodic table, but no names. Why? The American Chemical Society standard final exam expects you to know that, for example, the symbol for potassium is K, and not Po! 1A 2A 3B 4B 5B 6B 7B ----8B----- 1B 2B 3A 4A 5A 6A 7A 8A Please know names and formulas of the elements inside the red box. Mon 9-16-09 …especially the “C’s”! 12 “Main Group” elements 1A 2A Mon 9-16-09 3B 4B 5B 6B 7B ----8B----- 1B 2B 3A 4A 5A 6A 7A 8A 13 1A 2A 3B 4B 5B 6B 7B ----8B----- 1B 2B 3A 4A 5A 6A 7A 8A “Transition” elements Mon 9-16-09 14 1A 2A 3B 4B 5B 6B 7B ----8B----- 1B 2B 3A 4A 5A 6A 7A 8A Lanthanides & Actinides Mon 9-16-09 15 Alkali metals: exothermic reaction with water 2 Na + H2O H2 + 2 NaOH + heat Mon 9-16-09 16 Winner of the 2002 Ig Nobel Prize in Chemistry – Theodore Gray and his hand-carved periodic table. http://www.theodoregray.com/PeriodicTable/index.html (Check out “sodium party” link at this web site.) Mon 9-16-09 17 Excellent book! Personal history of the young Oliver Sacks who as a kid was fascinated by the Periodic Table. $10 from Amazon.com Mon 9-16-09 18 Alkaline earth metals Halogens These elements exist as diatomic molecules X2 Mon 9-16-09 19 -Cations -Anions -Ionic Compounds Mon 9-16-09 20 Ionic compounds contain CATIONS (+) and ANIONS (-). CATION “CAT-eye-on” The “t” looks like “+” CA+ION. ANION “AN-eye-on” (opposite charge from cation) The whole compound is electrically neutral. Total amount of (+) charge = total amount of (-) charge. Mon 9-16-09 21 CATIONS Metals form exclusively IONIC compounds, as Cations (+). Metal atoms in Groups 1A, 2A, and 3A lose electrons to form “inert gas configuration”. That is, same number of electrons as the NEXT SMALLER inert gas. 1A 2A 3A Mon 9-16-09 22 Potassium ion K+ forms from K atom by… Adding a positron (+1) Removing an electron (-1) Adding two positrons and removing one electron. 75 9 po s. ... el in g dd A em ov R tw in g o an po si a in g dd A Mon 9-16-09 .. 4 t.. . 1. 2. 3. 23 Potassium ion K+ forms from K atom by… 1. 2. 3. Adding a positron (+1) Removing an electron (-1) Adding two positrons and removing one electron. Positrons exist (inside accelerators), but have almost nothing to do with chemistry. K atom contains 19 protons (+19) in the nucleus and 19 electrons. When you remove an electron, there are still 19 protons, but only 18 electrons. 19 – 18 = +1 Mon 9-16-09 24 Group 1 atoms: Li Li+ + one electronLi+ has the same number of electrons as He atom. Mon 9-16-09 25 Group 2 atoms: Mg Mg2+ configuration. Mon 9-16-09 which has Neon electron 26 What is the charge on a barium (Ba) ion (as commonly found in nature)? 55 -2 -1 0 +1 +2 12 Mon 9-16-09 2 0 1 8 6 -1 6 -2 1. 2. 3. 4. 5. 27 What is the charge on a barium ion (Ba) (as commonly found in nature)? 1. 2. 3. 4. 5. -2 -1 0 +1 +2 All group 2A elements, including Mg, form the +2 ion in compounds. Mon 9-16-09 28 Transition metals have various charges: from +1 to +4. Mon 9-16-09 29 Cations, continued. The ONLY non-metal, polyatomic cation we will encounter is ammonium ion NH4+. Hydrogen ion H+ NH4+ NH3 Mon 9-16-09 Ammonia 30 Anions -monatomic anions -polyatomic anions Mon 9-16-09 31 These elements occur as monatomic anions Xy y= -3 -2 -1 NAME: N3- is Nitride Nitrogen Mon 9-16-09 32 Polyatomic ions - like a molecule, but with total charge > or < 0. All but two contain O, so they are called “oxoanions”. You need to KNOW NAMES and FORMULAS of these ions. This is your chemistry vocabulary. Table 2.4 p. 107 And Oxoanion Table on the course website. +1 -1 OH(hydroxide) NO2- (nitrite) NO3- (nitrate) ClO- (hypochlorite) ClO2- (chlorite) ClO3- (chlorate) ClO4- (perchlorate) CN(cyanide) CH3CO2- (acetate) MnO4- (permanganate) HCO3- (hydrogen carbonate) HSO4- (hydrogen sulfate) Mon 9-16-09 H2PO4- (dihydrogen phosphate) NH4+ -2 CO32- (carbonate) SO32- (sulfite) SO42- (sulfate) CrO42- (chromate) Cr2O72(dichromate) HPO42- (hydrogen phosphate) -3 PO43(phosphate) 33 Compounds y= -3 -2 -1 Ionic compound between lithium and sulfur: Li2S Lithium ALWAYS forms 1+ cation. Sulfur ALWAYS forms (in monatomic ions anyway 2- anion. Therefore need 2x as many Li as S. Mon 9-16-09 34