Atomic Physics II

Hydrogen Atom Model

Plumb Pudding Model (1897)-  Joseph John Thomson proposed that the atom was a sphere of positive electricity (which was diffuse) with negative particles imbedded throughout after discovering the electron, a discovery for which he was awarded the Nobel Prize in physics in 1906.

Thomson Model

http://galileo.phys.virginia.edu/classes/109N/more_stuff/Applets/rutherford/rutherford2.html

Geiger-Marsden Scattering Experiment

Rutherford Model

http://galileo.phys.virginia.edu/classes/252/Rutherford_Scattering/Rutherford_Scattering.html

http://galileo.phys.virginia.edu/classes/109N/more_stuff/Applets/rutherford/rutherford.html

Rutherford Scattering experiment

http://chemweb.chem.pitt.edu/pictures/vd02_004.htm

http://www.chem.rochester.edu/~chem131/wkshp/rutherford.mov

Bohr Atom

http://galileo.phys.virginia.edu/classes/252/Bohr_Atom/Bohr_Atom.html

3

2

42

1

mr

e

o

3

2

2

2

4

1

mr

e

r

v

o

22

2

1

4

1mv

r

e

o

r

vf

2

1

2

r

e

r

e

r

e

ooo 84

1

8

1 222

r

eE

o8

2

Total Energy of the electron in the hydrogen atom

r

mv

r

e

o

2

2

2

4

1

r

emv

o

22

8

1

2

1

r

emvEenergyTotal

o

22

4

1

2

1

Radius of orbital electron in the hydrogen atom

mE

er

o

112

103.54

1

2

1

r

eE

o8

2

22

22

1122

2

3

22

42

222

2

2

42

222222422

6.131

88

1029.54

4

1

2

nna

e

r

eE

mawhereanme

nr

mr

n

rm

nmrmr

r

e

rm

nnrm

nhnmr

ooon

ooo

n

o

Energy Levels on hydrogen atom

2

6.13

nEn

Rydberg constant and Atomic spectrum

The frequency of the radiant energy is Eh

where h is the Plank constant.

22

21

212

12

12

11

8

1

nnca

e

c

EE

c

hEEh

candEEE

oo

1 1 1

12

22

R

n n and R

me

chm

o

4

2 3

7 1

810974 10

.

In particular if n1 = 2 n2 = 3, 4, 5, ....... this series is known as Balmer series.

Other series : n1 = 1 n2 = 2, 3, 4, ....... Lyman

n1 = 2 n2 = 3, 4, 5, ....... Balmer

n1 = 3 n2 = 4, 5, 6, ....... Paaschen

n1 = 4 n2 = 5, 6, 7, ....... Brackett

n1 = 5 n2 = 6, 7, 8, ....... Pfund

(n2 = ) of Paschen series with n2 > 3 and n1 = 3

and the corresponding energy.

Example 4.1

Calculate the limiting value

eVhc

E

mnwithnn

51.1

102.811

10097.11 7

222

21

7

4.31 Emission spectra

Line spectra

- separate bright lines with definite wavelength- produced by luminous gases at low pressure in the discharge tube- the atoms are far apart not to interact with each other- no 2 elements give the same spectrum

Band spectra

Spectrum produced by molecules or molecular vapour

- several well defined groups / bands of lines- closed together- obtained from molecules of glowing gases heated / excited at low pressure- arise from the interaction % atoms in each molecules e.g. blue inner cone of a Bunsen burner flame

Continuous spectra

-emitted by hot solid and liquid also by hot gases at high pressure

-atoms are so closed that interaction is inevitable

- all wavelengths are emitted

The Absorption Spectra

-line, band, continuous spectra are again obtained

- when white light passes through a cooler gas or vapour, the atom absorb the light of the wavelengths which they can emit and then re- radiate the same wavelengths almost at once but in all directions

- dark lines occur against the continuous spectrum of white light exactly at those wavelengths which are present in the line emission spectrum of the gas or vapour e.g. absorption spectrum of iodine vapour

Sun’s spectrum & the Fraunhofer dark lines

prescence of a layer of cooler gas round the sunabsorption spectrum

http://tycho.bgsu.edu/~laird/phys655/class/IC.html

END

http://micro.magnet.fsu.edu/electromag/java/rutherford/