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04CHM11404_128

04CHM11404_128 - CHEM 114A Spring 2004 Wed Jan 28th 2004...

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Unformatted text preview: CHEM 114A Spring 2004 Wed. Jan. 28th 2004 Lecture No. 4 website wwwpublic.asu.edu/~caangell Chapter 2. Concluded MOlCCUlGS have particular structure which represents the lowest energy arrangement of the elements in the compound. ‘1 CH4 carbon tetrahydride..(Methane) H-Q-H . . H CO2 carbon dIOXIde Hydrocarbons C2H6, C2H4, CZHZ Ethane ethane.ethylene elhyne (acetylene) '5 / \ ’ 1- .. c .. g .. c =. C. - C. 3 c - / fir. I In CGH6 hexacarbon hexahydride (benzene) #0 Composition in wt % = mass of element x 100 —— - C" H6 “ “"— total mass (Ad- I" c’ H. km‘I-‘wg will it nx‘ :13" qq..q' #‘ a 171?} '18 '1! VHJ Molecular formulae vs empirical formulae. Finding an empirical formula from a chemical analysis. Benzene. Shape of molecule, 7.6% H, 92,4%C A Sham-c l o o a L 4.5m}; Macs: q: C. 5'3 A” ‘ “‘0 fit H a. has : 514 I1- u. . i .. . 1 a .. 1 t. 1. 3:434‘ m: oak 53 “N. She “of" no Therefore, Empirical Formula is C. H ‘ Chemical formula is C‘sl-I6 (same integral numEer applies to all subscripts Representations of molecular shapes. Ball and stick Space-filling models (Figs 2.16, 2.17 (8"1 Ed) Ionic compounds. NaCl, MgClz, AlC]3 and predictability of formfilae $.4- - Na Cl. 3 M “Cl!” Rub) Change from halogen o chalcogen CaClz, CaO, MgO (same structure as NaCl: “rocksalt” structure in 1' I- NC' 0 M5" 0" ‘8 M3 0 It“. 3 Rafi-«g 0-: NI. CL Nova Why? Because ions: balancing charges (total positive charge = total negative charge) Very common anion type: Oxxanions e.g. dry-wall Ca§24 (ZHZO) (plaster of Paris) 1ft ' su aeamon SO“;M (u “('3‘ {In 50.. , \ 3 Pd‘qfiom’. s Canon N“S°“ cor No; A Other oxyanions: ‘P O '1 - 50‘t - C l 0; plus Putz Perchlor- ‘P o g ' ‘33 ’kO‘P‘KZ“ And their compound formulae, by charge balance (ternary compounds) 4- - 0 ma», ‘ a, M Md 0.. CL 0 ‘ Compounds of hydrogéncgnd‘eltfanions (acids): .3. a team‘- 5“! ?§p&5fi rpouavft: ban“bflfl?w€ fig Hue, ‘ mm. . Ha. Mm" sougfisee the pattern? ) H B!- . H CH Patterns in chemistry. . .look for them to simplify your learning. . .all facts in chemist-ti are connected. Read section 2.7 C. 5' “ “M "‘ 9) Figure out the formula for aluminum sulfate, and magnesium nitride Do Problems: as: )I out Ed Chapter 3. Chemical Calculations. We are skipping it: too much time and pain. Need the time for engineering materials. (We’ve already discussed finding a chemical formula from the composition in wt%.) One thing to take from it, though: The Mole concept. fl The idea behind the mole concept is this: Atoms are too small to deal with individually. We always make measurements involving LOTS of them. Let’s decide on a standard number of them. .. a sort of reference number for making measurements of volume, energy etc. — a number that is the same for all our calculations and tabulations. The number we choose is the number of hydrogen atoms in 1 g (almost) of H atoms. It is exactly the number of carbon atoms in 12 g of 12C, by international agreement. We call this number, one MOLE. (Also Avogadro’s number) 6.023 x 1023 ’- So the MOLAR volume of water (density 1 g/ml) is 18 ml, because one mole of water weighs 18 g. Accordingly, all atomic weights are the masses of Avogadro’s number of the atoms in question (which will have a fixed distribution of isotopes) expressed without units (they are written without units because of the way they are defined relative to the mass of the standard 12C). Another example: Heat of formation of oxygen atoms from oxygen molecules, expressed by the chemical process will be tabulated in joules per mole of oxygen decomposed. AH = 247.5 kJ/mol 02 The energy of ionization of sodium will likewise be tabulated in the energy needed to remove one mole of electrons from one mole of Na atoms. (107.7 lemol) OK. . .. Ready for Chapter 4.. reactions in solutions ~— AQUEOUS SOLUTIONS ...
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