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Welcome to 3.091

Lecture 3

September 14, 2009

Atomic Models: Rutherford & Bohr

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Periodic Table Quiz

Name Grade /10

Image by MIT OpenCourseWare.

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La Lazy

Ce college

Pr professorsNd never

Pm produce

Sm sufficiently

Eu educatedGd graduates

Tb to

Dy dramatically

Ho help

Er executives

Tm trim

Yb yearly

Lu losses. source unknown. All rights reserved. This image is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.
http://ocw.mit.edu/fairusehttp://ocw.mit.edu/fairusehttp://ocw.mit.edu/fairuse

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La Loony

Ce chemistry

Pr professorNd needs

Pm partner:

Sm seeking

Eu educatedGd graduate

Tb to

Dy develop

Ho hazardous

Er experiments

Tm testing

Yb young

Lu lab assistants.

cannot be referring

to 3.091!

must be the other

chemistry professor

source unknown. All rights reserved. This image is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/fairuse.
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CEase not I to slave, back breaking to tend;PRideless and bootless stoking hearth and fire.

No Dream of mine own precious time to spend

Pour'ed More to sate your glutt'nous desire.

SMelting anew my ten-thousandth hour

EUtopia forever I eschew.Growing Dimmer is my fleeing power

To Bid these curs'ed problem sets adieu.

DYing away whilst thy hosts are fought

HOpeless I come should in lecture I doze.

ERgo, like a sad slave, stay and rest nought.

Then Must I tool and toil while fatigue grows.Yet, Bloody though I must be, and quite ill

Light the Universal abyss I will.

57

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Lanthanum

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La3*

Courtesy of MIT Student. Used with permission.

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The Structure of the Atom

status report ca. end of the 19th century

* atom is electrically neutral

* -ve charge carried by electrons

* e- has very small mass

bulk of the atom is +ve,

most mass resides in +ve charge

Question:

what is the spatial distribution of charge inside an atom?

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Figure 1.18


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Figure 1.19

Paper0.5- cm lead10-cm lead

rays

particles

particles


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Rutherford-Geiger-Marsden experiment


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b

Marsden's Analysis

Scattering of an -particle which approaches a heavy nucleus with an impact parameter b.

qTrajectory of incident

particle

gold nucleus


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principles of modern chemistry:

* recognize patterns

* develop a quantitative model that

- explains our observations

- makes predictions that can betested by experiment

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Bohr Postulates for the Hydrogen Atom

1. Rutherford atom is correct2. Classical EM theory not applicable to orbiting e-

3. Newtonian mechanics applicable to orbiting e-

4. Eelectron = Ekinetic + Epotential

5. e- energy quantized through its angular momentum:

L = mvr = nh/2, n = 1, 2, 3,

6. Planck-Einstein relation applies to e- transitions:

E = Ef- Ei = h = hc/

c =

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L = mvr = nh/2, n = 1, 2, 3,



c =

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L = mvr = nh/2, n = 1, 2, 3,



c =

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L = mvr = nh/2, n = 1, 2, 3,



c =

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0 500 1000 1500 2000 2500 3000

5000 K

4000 K

3000 K

Radiationintensity

Wavelength (nm)

Classical prediction6000 K

E = h

Planck suggests that light is composed of energy

packets or quanta. The elementary unit of e-m

radiation is thephoton.

InfraredVisibleUV

6000 K


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L = mvr = nh/2, n = 1, 2, 3,



c =

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source unknown. All rightsreserved. This image isexcludedfrom our Creative Commons

license.For more information,

seehttp://ocw.mit.edu/fairuse.
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source unknown. All rights

reserved. This image isexcluded from our Creative

Commons license. For moreinformation, seehttp://ocw.mit.edu/fairuse.
http://ocw.mit.edu/fairusehttp://ocw.mit.edu/fairuse

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Isotopes of Hydrogen

hydrogen1766 Henry Cavendish, London

deuterium

1931 Harold Urey, Columbia U.

tritium

1934 Ernest Rutherford, Cambridge U.

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Dalton proposes the

indivisible unit of an

element is the atom.

1803

Thomson discovers electrons,

believed to reside within a

sphere of uniform positive

charge (the "plum pudding"

model).

1904

Rutherford demonstrates the

existence of a positively charged

nucleus that contains nearly all

the mass of an atom.

1911

Bohr proposes fixed circular

orbits around the nucleus

for electrons.

1913

In the current model of the

atom, electrons occupy regions

of space (orbitals) around the

nucleus determined by their energies.

1926


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J. J. Thomson (1856-1940)

Cathode ray = Charged particle = Electron (1897)

charge-to-mass ratio of electron (1897)

J.J Thomson

"Plum pudding" model of

atom (1904)

Robert Millikan (1868-1953)

Charge and mass of electron

(1909)

James Chadwick

(1891-1974)

Neutron (1932)

Ernest Rutherford

Proton (1920)

Ernest Rutherford

Nuclear model of atom (1911)

Ernest Rutherford

(1871-1937)

and particles (1898)

Marie and Pierre Curie

(1867-1934, 1854-1906)

Radioactive elements

polonium and radium (1898)

Henri Becquerel (1852-1908)

Uranium emits rays that fog

photographic film (1869)


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3.091SC Introduction to Solid State ChemistryFall 2009

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