171_ProbSet_2_key_2008

171_ProbSet_2_key_2008 - CHEM171 ---$olutions to Homework 2...

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Unformatted text preview: CHEM171 ---$olutions to Homework 2 1. Orbital depicted has 2 angular nodes (dz2 orbital), and one radial node. Given the angular nodes and axes depicted, and that radial nodes bisect all lobes of a given angular distribution function, and that each lobe is split into only two, it is a 4d,2 orbital. 2. Lowest energy is achieved when electrons are as far away from each other as possible (half filled shell) which minimizes electron-electron repulsion 3. The effective nuclear charge of a cation is much larger than a neutral atom. The second ionization energy of carbon ionizes an electron from a cation, while the first ionization energy of boron ionizes an electron from a neutral atom. 4. K+ = 1522522p"3sz3p6 and CI' = 1522322p63523p" Zeff* for K+ = 19 - [(2 x 1.0) + (8 x 0.85) + (7 x 0.35)] = 7.75 Zeff* for Cl' = 17 - [(2 x 1.0) + (8 x 0.85) + (7 x 0.35)] = 5.75 A higher effective nuclear charge means a stronger force of attraction is experienced between the electron and the nucleus, therefore the size of Cl' is greater than Ki 5. Br 2 (lsz)(252,2p6)(3$2,3p°)(3d‘°)(4sz,4p5) The 4p electron in bromine will be shielded by (lsz)(232,2p6)(352,3p6)(3d1°)(4sz,4p4) = 35 - [(1.0 x 2) + (1.0 x 8) + (0.85 x 8) + (0.85 x 10) + (0.35 * 6)] = +7.60 0 Slater's rules have two ma jor flaws- assuming the equal penetration of s and p electrons (symmetry isn't taken into account), and neglecting the effect of electron pairing in orbitals. A p orbital is less penetrating than an s electron, and shields significantly less well than an s electron of the same energy. In this case, the shielding of the 4p orbitals is overestimated - since the electron being shielded is also 0 4p orbital, and hence the electron actually feels a greater Zeff* than calculated by Slater's Rules All other things being equal, covalent bonds between identical elements (Fl-Fl, Cl- Cl, Br-Br) should decrease in strength going down a column because of the longer distances between the nuclei. Therefore, bond dissociation energies should follow Fl > Br' > CI, but they don‘t. Given fluorine’s small atomic radius and high electronegative character, the F-F bond is destabilized by electron-electron repulsion as the two nuclei approach each other. This leads to lower than expected bond dissaciation energies in F-F. 4) i'PsPi c) mac-Que] ll) iota-g; - _- in sec? \ 3)Ig| 4.. c_u ) 5 <le i; q .I If." :t\ 1.3.9 d .'.a‘a> J S h- e- e. c. ‘ ) ‘9‘ leg ‘g on» lE' "T" {in _ ‘\ 1)|l.=-é.—E'I M) ri—S'.-’Ei n if- —-Ei - i " ‘ i ‘E‘ “1‘ \Li ‘\ 0) N“ v) ’s’Pxe wlfifl ‘, l s \a l H l2\ ig- lol w” _ — - u t) 5\ fil—F '35-- El ‘) ’orxg‘sx o// \o ‘iE-i aha“ ‘ u) ’ 1"; v) N“§"°~ -' “3 I9?“- W , r \ 3’ “of *3. ""’“ w . C' x N'R‘ I") 0// \no" ) \6 aha 9' ‘9‘. gal" sr-é .— 5305: 291‘ y .. *3 ) "" win-H "°“ w :23 “"" a I fry?” “’“d V a mu. v (rm eh- m 1‘ “M “h. M on a. ) w... u 9L \nM (A... IF. it: #313 a-«bw’r "” “I \ | ’E‘ ' k l Std-rd“: 0k ’1‘ m "haunt-h") ‘ NI- *3 w “a dfinf-fi-n-cgal’o' fizzy} WV aunt-k W «mils —> It (L‘th I: dun»? ,z. n... ("at-ant... rum: n) {37 .‘J ‘3 I a) ‘ urinal 3 duh“! a W maul ! ...
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This note was uploaded on 01/29/2010 for the course CHEM 142725201 taught by Professor Kaner during the Fall '08 term at UCLA.

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171_ProbSet_2_key_2008 - CHEM171 ---$olutions to Homework 2...

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