Chem 125 Lecture 19/4/02

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This material is for the exclusive use of Chem 125 students at Yale and may not

be copied or distributed further.

It is not readily understood without reference to notes from the lecture.

Enter on the white card in this order (no need to write the word “Name”, etc.)

Name (pronunciation hints if necessary)

Prefer to be Called (e.g. Jay, not Jethro)

Hometown with zip code

E-mail

Name of your best science teacher (with subject)

Prospective major(s)

Put comments or questions on back.

Exam Dates

10 lectures

Sept 27

9 lect

Oct 21

9 lect

Nov. 13

10 lect Dec 17

100 pts

100 pts

100 pts

300 pts

Semester grade biased by faithfulness in timely problem set submission

HELP !

Other Chem 125 students!Alumni

Text: Introduction to Organic Chemistry (4th ed) Streitwieser, Heathcock, and Kosower

Lecture Notes (in-class questions)Course web site: www.classes.yale.edu/chem125a

Assigned problems or questions

Instructor : Prof. J. M. McBrideTAs : Roger Cole (Mon/Thurs evenings ? )

Teaching Interns: Diana Mandelker & Josh Dunn

Problems For Friday: 1) Which two class members live nearest you?2) What are the three most common items of advice from course veterans?3) Send as e-mail to Roger.Cole@yale.edu

For Monday:(Problems from Text - Ch 2: 1,2, 4a-e, 5a-e)1) Are Lewis Structures correct?2) What do they show?

How do you know?

John McBride (age 3)

How do you know?

John McBride (age 29)

Finger Writes

Shows Joshua

Asks question of Class

Class

Do not suppose that I was a very deep thinker, or was marked as a precocious person. I was a very lively imaginative person, and could believe in the "Arabian Nights" as easily as in the "Encyclopaedia." But facts were important to me, and saved me. I could trust a fact, and always cross-examined an assertion. So when I questioned Mrs. Marcet's book by such little experiments as I could find means to perform, and found it true to the facts as I could understand them, I felt that I had got hold of an anchor in chemical knowledge, and clung fast to it.

Michael Faraday, 1858

If they say to you science has shown such and such, you might ask, "How does science show it - how did the scientists find out - how, what, where?" Not science has shown, but this experiment, this effect has shown.

When someone says science teaches such and such, he is using the word incorrectly. Science doesn't teach it; experience teaches it.

Learn from science that you must doubt the experts…Science is the belief in the ignorance of experts.

Richard Feynman (to National Science Teachers Assn 1966)

Why cite Feynman?

No.Because he deserves credit for saying something that is true

and saying it very well .

Because he is an expert?

Munowitz (fall 73)

Munowitz review facts

Budiansky Cover

How do we know?

What are the most importantTOOLS?

G.N. Lewis(1875-1946)

& his

Cubic Octet

Lewis on running board

G. N. Lewis

Octet "Explains" Periodicity, Electron Transfer(1902)

Octet Predicts Shared Pair Bonding

?

shared edge

shared face

G.W. and Robert Robinson (1917)

Partial Valencesto “explain” trivalent and pentavalent N???

What Lewis Added

Text p. 16“empirical rules for assessing the relative importance of the resonance structures of molecules and ions.

1. Resonance structures involve no change in the positions of nuclei; only electron distribution is involved.

3. The more important structures are those involving a minimum of charge separation, particularly among atoms of comparable electronegativity. Structures with negative charges assigned to electronegative atoms may also be important.

2. Structures in which all first-row atoms have filled octets are generally important; however, resulting formal charges and electronegativity differences can make appropriate nonoctet structures comparably important.LORE

Is it True?

Force Laws

Levitator by Martin Simon (UCLA)

Eppur sta fermo

QuickTime™ and a decompressor

are needed to see this picture.

QuickTime™ and a decompressor

are needed to see this picture.

Thanks to Prof. André Geim

Frog

In systems governed byinverse-square force laws

there can be no local minimum (or maximum)

of potential energy.

Earnshaw's Theorem(1839)

Visualizing Earnshaw - Coulomb's Electrostatics

A positive particle has a local maximum or minimum of energy only at the location of

another charged particle, never in free space.