ch10-4web

Chem 5 Chapter 10 The Periodic Table and Some Atomic Properties Part 4 November 8, 2002

Noble Prize in Chemistry, 2002

Kurt Wüthrich

John B. Fenn

Koichi Tanaka

“The Nobel Prize in Chemistry for 2002 is being shared between scientists in two important fields: mass spectrometry (MS) and nuclear magnetic resonance (NMR). The Laureates, John B. Fenn and Koichi Tanaka (for MS) and Kurt Wüthrich (for NMR), have contributed in different ways to the further development of these methods to embrace biological macromolecules. This has meant a revolutionary breakthrough, making chemical biology into the "big science" of our time. Chemists can now rapidly and reliably identify what proteins a sample contains. They can also produce three-dimensional images of protein molecules in solution. Hence scientists can both "see" the proteins and understand how they function in the cells.” http://www.nobel.se/chemistry/laureates/2002/public.html

Mass Spectroscopy for Macromolecules

Electrospray technique

Time-of-flight mass spectrometer http://www.nobel.se/chemistry/laureates/2002/chemadv02.pdf

Approach for high throughput microbial proteomics Identification of more than two thousand proteins in a bacterium

Dimension one

Capillary LC-FTICR 2-D display of peptides from a yeast soluble protein digest

2-D display of detected peptide “spots” >160,000 isotopic distributions corresponding to >100,000 polypeptides detected

2,500

2,243

1,987

1,731

MW 0

42

84

126

168

1,475

Liquid columntography elution time (min) 1,218

Dimension two

962

706

450 24

750

m/z

1000

1250

1500

33

44

52

62

71

Time (min) Smith et al., Proteomics, 2, 513-523 (2002)

Electrons have spin. So do protons. ∆E = hν is sensitively dependent on the surrounding electrons, i.e chemical bonds around the proton. Low resolution NMR spectrum of ethanol Transition at Radio frequency

In the presence of a uniform external magnetic field Nuclear Magnetic Resonance (NMR) Spectroscopy

Radio frequency

Nuclear Magnetic Resonance Spectroscopy of Macromolecules Determine the structures of proteins

Nature 418, 207 - 211 (2002)

Magnetic Resonance Imaging Non-uniform magnetic field

hν = Energy splitting is position dependent.

Position x x

http://www.washingtonopenmri.com/a2.htm

Freshman Seminar 22j For Spring 2003 Seeing by Spectroscopy William Klemperer

Professor William Klemperer

The seminar will explore diverse topics and areas of science in which spectroscopy — the observation of energy emitted from a radiant source — plays a leading role. Although there are many practical applications of spectroscopy, the seminar will concentrate on selected topics from chemistry, physics, astronomy, and atmospheric science. Among these are the structure of molecules from the simple measurement of the bond length of a diatomic species to finding out the structure of proteins. The seminar will emphasize spectroscopy as the basis for remote sensing, choosing the grand topic of looking out — astronomical observations and seeing what is in the universe. Participants also will study (Nuclear) Magnetic Resonance Imaging as a model for looking in. This seminar will exploit the great increase in understanding nature that occurred throughout the twentieth century as a result of the invention of quantum mechanics. Participants will cooperate in developing and maintaining a seminar web page. Although the seminar is directed towards students with an interest in physical science, the required background is not extensive since the seminar will not derive relations but rather state and use them. Participation will involve some use of computational packages. Freshman Seminar Program Web Pages

Magnetic property A paramagnetic atom or ion has unpaired electrons and the individual magnetic effects do not cancel out. A diamagnetic atom or ion has all electrons paired and the individual magnetic effects are canceled.

Gd3+ [Xe]4f7 4f

Summary

Closed shell most stable

Reducing Abilities of Group 1 and Group 2 Demos Comparison of the reducing ability of K and Ca for water

2 Li ( s ) + 2 H 2 0  → 2 Li + (aq ) + 2OH − (aq ) + H 2 ( g ) 2 Na ( s ) + 2 H 2 0  → 2 Na + (aq ) + 2OH − (aq ) + H 2 ( g ) 2 K ( s) + 2 H 2 0  → 2 K + (aq ) + 2OH − (aq ) + H 2 ( g ) Ca ( s ) + 2 H 2 0  → Ca 2+ (aq ) + 2OH − (aq) + H 2 ( g ) K being the most active metal among the four because of its lowest I.E.

Oxidizing Abilities of Halogen Elements Demo −

−

Cl2 ( g ) + 2 I (aq )  → I 2 (aq ) + 2Cl (aq ) Cl2 has higher oxidizing ability than I2. −

−

Cl2 ( g ) + Br (aq)  → Br2 (aq) + 2Cl (aq) This reaction (not shown) occurs, but very slowly.

Metals tend to lose electrons to attain noble gas electron configurations

Nonmetals tend to gain electrons to attain noble gas electron configurations.

Na(g) → Na+(g) + e[Ne]1s2

[Ne]

I1=496kJ/mol

Na+(g) → Na2+(g) + e- I2=4562kJ/mol [Ne]

[He]2s22p5

I = RH

I2 >> I1 because n = 3 Æ n = 2 That is why we do not see Na2+ around.

Z

2 eff 2

n

General Trends and Exceptions

2s22p1 E2p>E2s 2s22p3

Half full stable

4s23d10

4s23d104p1

It is important to write down the electron configurations!

Summary of Chapters 9 &10 •

Energy quantization explains three spectroscopic experiments: – Blackbody radiation

E= hν

– Photoelectric effect

hν = hν0+ 1/2mu2

– Hydrogen atom lines

hv = ∆E = E f − Ei =

RH RH − 2 2 ni nf

•Two key concepts of quantum mechanics – Particle-wave duality

λ = h / p de Broglie wavelength

– Uncertainty principle

∆x ∆p ≥ h/4p

• Schrödinger equation – Probability interpretation of wave functions (orbitals) Ψ2 − probability density – In an atom, four quantum numbers, n, l,ml, ms for an electron – Shapes of the orbitals

s,p,d,f

Number of nodes, radial and angular nodes

• Periodic table – Screening and penetration, Zeff

Zeff=Z – S

– Electron configurations - Aufbau process –Minimizing energy, Pauli Exclusion, Hund Rule – Qualitative explanation of the periodic trends in connection with the electron configurations

Ionization

E=0

Ι.Ε. = − Εn

e-

En = − RH

Electron affinity

Z eff2 n2

e-

Emission

Spectroscopy

hν

Transition between two orbitals 2

hv = ∆E = RH

Z eff 2 i

n

2

−

Z eff n

2 f

hν

n=1

r

n=2

n=3 n=4

absorption

c = v/λ

Atomic or ionic radius

n 2 a0 rn ∝ Z eff

average size of an orbital not orbit