Exam 2 results Homework 7 posted Due Friday

• • Exam 2 results Homework 7 posted. Due Friday 10 November in class Read pp 178 -183…end of Ch. 5 Read Chapter 6: 193 -203 (Doing the Lewis Octet Dance)

The road trip through mole land so far… • Basic mole-mass-count conversions ( divide up, multiply down) • Mole ratio conversion within a compound (`body parts’ relationships)

The mole road ahead. . . • % composition problems and combustion analysis (pp. 94 -103) : moles level 2 b

Why bother with all of this ? ?

% composition problems: using mole concept to convert weights to formulas Sample % composition problem #1 A compound of N and O contains 63. 63 wt % N and 36. 36 wt % O. What is the empiric formula of the compound ?

Definition: empiric formula= mole ratio of elements in a compound expressed in lowest whole numbers Example: CH 2 O = empiric formula of glucose (sugar we metabolize) We already did this early on…but a quick review ?

Empiric formulas (continued) CH 2 O = empiric formula of glucose (sugar we metabolize) Actual molecular formula (what it really has in atom count): C 6 H 12 O 6= (CH 2 O)6 Sugar =Carbo hydrate

Which formulas below are empiric (= lowest common denominator form) ? ? C 3 H 6 O 3 ÷ 3 NOT EMPIRIC CH 2 O

Which formulas below are empiric (continued) N 3 F 7 ? ? EMPIRIC… 3 & 7 have no shared factors

Which formulas below are empiric (continued) H 3 P 9 O 12 S 5 EMPIRIC (3, 9, 12 ? ? divisible by 3…but 5 is not)

% composition Problem 1: empiric formula determination A compound of N and O contains 63. 63% N and 36. 36 %O. What is the empiric formula of the compound? let’s do it on the board…

Sample problem #1; SUMMARIZED OFFICIAL NAME… =>N 2 O element N O w(g) 63. 63 36. 36 Dinitrogen monoxide =Laughing gas AW=Atomic wt (g/mol) 14 16 n=w/AW moles 63. 63/14= 4. 545 36. 36/16 = 2. 273 n nmin 4. 545 = 2 2. 273 =1 2. 273

Joseph Priestley 1772 http: //www. youtube. com/watch? v=_Ha-Zr. UPJ_E

% composition problem 2: An oxide of nitrogen contains 46. 7 wt. % N and 53. 3 % O. What is it’s empiric formula ? A. NO 3 B. NO 2 C. N 2 O D. N 3 O 7 E. NO F. None of the above

% composition Problem 3: empiric formula determination with a twist A compound composed of C, H and O is 48. 64% C and 8. 16 % H and 43. 2 % O by mass. What is the empiric formula ? Answer: C H O 1. 5 3 1 3 element Mass, g Atomic n=mass wt(g/mol) Atomic wt n/nmin C 48. 64 12 48. 64/12= 4. 05 H 8. 16 1 O 43. 2 16 8. 16/1= 8. 16 43. 2/16= 2. 70 4. 05/2. 7 1. 5*2= 3 =1. 5 ? 8. 16/2. 7 3. 0*2= 6 =3. 0 2. 7/2. 7= 1*2= 1 2 6 x FACTOR 2

Where we’ve been…. Rutherford & Bohr 1910 1) Atomic structure & dimensions 2) p+no , e- bookkeeping 3) Crazy quantum models

Where we’ve been…. In the land of the spectroscopists: 1 s 2 2 p 6 3 s 2 3 p 4 …… Describing atoms by electronic configurations implied by observation and predicted by Periodic table spectroscopy `fugetabout theory…. let the line spectra rule or I breaka your face !

Where we’ve been… Dalton 1805 AD 1)Law of constant proportions 2)Law of multiple proportions Moles till we drop…. .

* We know how to use the fancy math…but our `style ‘ is visual and practical The Americans land… G. N. Lewis 1925 AD: Teaches us how to use the Periodic table to rationalize ionic and covalent compound formulas without breaking a sweat…The Big Kahuna of an American-style Chemistry that looks at the big picture and uses simple, intuitive models. (sans calculations …)*

Legacies of the American chemist: Gilbert Newton Lewis American Chemist UC Berkeley “at work” ~1930 Before Lewis: UC Berkeley Chemistry Building ~1915

Chemistry `Quad’ UC Berkeley 2013 + more `on the hill’ at L-L Labs

As young chemistry nerd …Young Doc Fong sits in here staring every day at a 4’x 6’ photo of… The House that Lewis Built: Lewis Hall of Chemistry UC Berkeley

Lewis `octet’ model (see also steps 1 -4 pp 194) The Entire Lewis model In a nutshell: 1) All bonds contain two electrons. 2) All elements except H and He 1 seek an outer (valence) shell of 8 electrons. 3) If you can –minimize formal charge. 4) For elements from P onwards, you can break the octet rule and use rule 3. 1 H and He are satisfied with 2 electrons= `duet’ rule

IN-CLASS BOARD OCTET RULE PRACTICE WITH: : Diatomics O 2 tri, tetra-atomics CO 2 H 2 O OF 2 COCl 2 N 2 CO

IN-CLASS BOARD OCTET RULE PRACTICE (continued): : • Multi-atom, neutral compounds 1 Tri, tetratomics CO 2 H 2 O OF 2 1 How COCl 2 do we know what bonds to what ? Some rules of thumb: a)Atoms closer to center of Periodic Table are in center of molecule b)Molecules tend to be symmetric.

Which structure below satisfies the Lewis octet rule for SOBr 2 ? A. all single bond B. S=O double C. S=Br double D. None of the above

IN-CLASS BOARD OCTET RULE PRACTICE WITH: : Diatomics O 2 N 2 CO tri, tetra-atomics CO 2 H 2 O OF 2 COCl 2 oxyanions NO 3 - CO 3 SO 42 -

Which is the best structure for SO 32 - that satisfies the Lewis octet rule A. All single S-O B. 1 S=O, 2 S-O C. 2 =O, 1 S-O D. All S=O

IN-CLASS BOARD OCTET RULE PRACTICE WITH: : Diatomics O 2 N 2 CO tri, tetra-atomics CO 2 H 2 O OF 2 COCl 2 oxyanions NO 3 - CO 32 - SO 42 Non-Lewis octet H 2 SO 4 - SO 2 SO 3 SO 42

BEYOND THE OCTET RULE: FORMAL CHARGE UGLY CHEMICAL FACT OF LIFE #1: For elements starting with Si in the 3 rd row, the octet rule is often broken. EXAMPLE #1: BATTERY ACID (H 2 SO 4) From Experiment (Kuczkowski et. al. 1983) Lewis octet prediction for H 2 SO 4 structure