Atoms 1

En = - nh

emZ2

eff )1

)(2

(2

422

Atoms

tiny wonders worth studyingEnergy states of electrons in atoms are represented by this formula. Understand all the symbols and implications of this formula.

Atoms 2

The Hydrogen Spectrum

Wave number = – R (–– – ––) 1 1nf

2 ni2

Balmer’s findingBalmer series, ni = 2; snd nf = 3, 4, 5, ...

Rydberg’s formula

Rydberg constant

Atoms 3

Energy States of e- in H

Atoms 4

The Discovery of X-raysRontgen’s letter publish in Nature (Jan 23, 1896) with a photo showing a hand skeleton of his wife proclaimed the discovery of X-rays. (imagine.gsfc.nasa.gov/docs/science/know_l1/history1_xray.html)

X-ray image of Mrs. Rontgen’s handImage of rabbit earspring8.or.jp/ENGLISH/general_info/overview/imaging.html

Tell the story of X-ray discovery.

Atoms 5

Generation of X-raysX-ray Generation by Cathode Rays

Filament and thermal electron emitterElectron beam

1000 V

X-rays

X-ray Spectra of Low and High Voltages

Number ofphotons

Photon energy

Highvoltage

Lowvoltage

What is the principle of X-ray generation?

Atoms 6

Characteristic X-rays and energy levels of electrons in elements

Target Material Dependent Lines ofX–rays.

Intensity

Energy h v

K (n=1)

L (n=2)

electronCharacteristic X-ray

What are characteristic X-rays and why they are generated?

Atoms 7

Moseley’s Law

Plot of Moseley’s Law

/ 109

3.0

2.0

1.0

25 30 35 40 45 50 55

Atomic No.

h

emZ eff )2

3(

2

422= h =

EK (n=1)

L (n=2)

electronCharacteristic X-ray

What is Moseley’s law and how it impacts science?

Atoms 8

X-ray Diffraction ExplainedDiffraction of X-ray Waves by Crystal Planes

X-raywaves

Typical diffraction diagram of a quasicrystal, exhibiting 5-fold or 10-fold rotational symmetry

Atoms 9

Crystal Structures Revealed by X-ray Diffractions

The Crystal Structure of Table Salt, NaCl

Only one layer is shown. The crystals consistsof many layers stacked on top of each other.

Tetrahedral Bonding in Diamond, Silicon,Zinc sulfide, Gallium Arsenide etc.

X-ray diffraction revealed structures of many substances and impacted science and engineering development. Two are shown.

Atoms 10

Becquerel’s Experiments Leading to the Discoveryof Radioactivity

Ag Br Photographic platewrapped in black paper.

Uraniumsalt

Image of uranium salt on plate

Discovery of Radioactivity

Methodology in Becquerel’s discovery of radioactivity is intriguing and interesting.

How do you explain the discovered phenomenon?

What & why?

Atoms 11

Bending of and rays by an Electric Field.

Properties of Radioactive Rays

What is radioactivity?

Atoms 12

Interpretation of Rutherford's alphascattering experiment

Most alpha particles are unaffected,few deviated by large angles.

Rutherford -particle Scattering Experiment

What is the alpha scattering experiment?

What did he observed, and how he explained it?

Atoms 13

Rutherford’s Conclusion

Radius of atoms: 1e-10 mH 37 He 50 Li 150 F 71 Fr 170

Radius of nuclei: 1e-15 m

rnuc= 1.2 A1/3 fm(1E-15)

Interpretation of Rutherford's alphascattering experiment

Most alpha particles are unaffected,few deviated by large angles.

The Rutherford Atoms

Atoms 14

Bohr applied the Idea of Max Planck, and used results from Rutherford. He made an assumprion:

m v r = h/2

His results are given next

Need a New Perception of the Atom

The Bohr Atoma tiny solar system

What is the Bohr atom?How did he arrive such a model? If U care

Atoms 15

Results of Bohr atom

m v r = h/2

r

vm

r

eZ 2

2o

2

4

oa

e

n

Z

o

2

2

2

42 En =

Energy States of an Electron in the H Atom

-13.6 eV

Free electron -Hau/ 2n2

-3.4 eV

-1.5 eV-0.85 eV

Energy States of Electrons in the Bohr Atom

Atoms 16

A Quantum Mechanical View of Energy States

Continuous versus Quantized States

A discretematerial world

In a large system, the energy states form a band. As the system gets smaller, energy states progressively became discrete.

Quantum mechanics is required to deal with microscopic systems and discrete energy states.

Atoms 17

Max Planck’s photon: E = h Rutherford atomThe Bohr atom (solar system) Heisenberg’s uncertainty principleLouis de Broglie (mater wave): = h / m v Schrodinger: Treat particles as waves

Traveling Waves

Standing Waves

The Development of Quantum Mechanics

What are the philosophies behind quantum?

Atoms 18

Quantum Mechanical View of Energy States of Electrons in the Atoms

Energy States of an Electron in the H Atom

-13.6 eV

Free electron -Hau/ 2n2

-3.4 eV

-1.5 eV-0.85 eV

Atomic Orbitals 4f– – – – – – – 4d– – – – – 4p– – –4s– 3d– – – – – 3p– – –3s–

2s– 2p– – –

1s–

Diagram energy states in atoms and explain the periodic table.

Atoms 19

Quantum Mechanics Led to and the Periodic Table of Elements

Atomic Orbitals 4f– – – – – – – 4d– – – – – 4p– – –4s– 3d– – – – – 3p– – –3s–

2s– 2p– – –

1s–

Electronic configurations of some light elements

Ne 1s2 2s22p6

F 1s2 2s22p5

O 1s2 2s22p4

N 1s2 2s22p3

C 1s2 2s22p2

B 1s2 2s22p1

Be 1s2 2s2

Li 1s2 2s1

He 1s2

H 1s1

Filling electrons in energy states gives the electronic configurations of all elements.

Atoms 20

The time line of our understanding of the

atomic nuclei

Some facts about atoms:

Radii of atoms ~ 1e-10 m (Å) most space occupied by electrons

Radii of atomic nuclei ~ 1e-15 m (fm) most mass concentrated in nuclei

Yin Yang and Primal Substance

1704 I. Newton – Solid body

1803 J. Dalton – atomic theory

1832 M. Faraday – electrolysis

1879 W. Crookes – discovered electrons

1886 W. Rontgen – X-rays H. Becquerel – radioactivity Goldstein – kanal rays

1897 J.J. Thomson – e/m ratio - Canal rays (H atom)

1898 E. Rutherford – studied radioactivity

1900 Soddy – transmutation of elements

1911 E. Rutherford – dense +ve nuclei

1914 H.G.J. Moseley – Moseley law

1922 N. Bohr – Bohr atom model

1923 de Broglie – particles as waves

1927 Heisenberg – uncertainty principle

1927 Cockcroft /Walton – split the atom

Atoms 21

Properties of Protons

Rest 1.6726231x10–27 kg mass 1.00727647 amu

938.2723 MeV

Spin ½

Magnetic 2.7928474 N

moment

Electric +1 atomic charge charge

1886 Goldstein discovered canal rays

1898 Wien and Thomson identified them as nuclei of H and determined some properties of protons

The atomic number used in Moseley’s law turns out to be the number of protons in the nuclei

Protons were thought to be fundamental particles

What is a proton?

Atoms 22

Discovery of NeutronsIt has been shown by Bothe and others that beryllium when bombarded by -particles of polonium emits a radiation of great penetrating power, .…

Be + = C + n + Energy B + n = Li +

It is to be expected that many of the effects of a neutron in passing through matter should resemble those of a quantum of high-energy, and it is not easy to reach the final decision between the two hypotheses.

Up to the present, all the evidence is in favour of the neutron, while the quantum hypothesis can only be upheld if the conservation of energy and momentum be relinquished at some point.

James Chadwick, Feb. 23, 1932How was neutron discovered, and what is it?

Atoms 23

Neutron Scattering Techniques

THE ROYAL SWEDISH ACADEMY OF SCIENCES

12 October 1994

The Royal Swedish Academy of Sciences has decided to award the 1994 Nobel Prize in Physics for pioneering contributions to the development of neutron scattering techniques for studies of condensed matter with one half to

Professor Bertram N. Brockhouse, McMaster University, Hamilton, Ontario, Canada, for the development of neutron spectroscopyand one half to Professor Clifford G. Shull, MIT, Cambridge, Massachusetts

Atoms 24

Applications of neutrons from a research reactor for studying structures and dynamics

Atoms 25

IsotopeDiscovery of neutron in atomic nuclei led to the concept of isotopes.

Atomic weight

Na 23Mg 24.3Cl 35.5Ar 40.K 39Ca 40Cu 63.5

Why atomic weights are not all integers?

Can atoms of an element have different number of neutrons?

What are isotopes?

What are isotopes?

What are stable isotopes of C, Cl, Ca?

Atoms 26

Deuterium and Isotopes of Hydrogen

Does hydrogen have isotopes?

How to separate isotopes?

How are their properties different?

H2 HD D2

Triple point /K 13.96 16.60 18.73

Vapor pressure 128.6 92.8 54.0 at TP

Heat of vapori- 117 159 197 zation at TP

Boiling point (K) 20.39 22.13 23.67

Heat of vapori- 903 1074 1225zation at BP

Harold C. Urey (1893-1981)

1934 Nobel Laureate in Chemistry for his discovery of heavy hydrogen.

Atoms 27

Urey Experiment About Life

The early Earth atmosphere of NH3, CH4, H2O, under discharge produced organic matter including aminoacids that are essential compounds for life form.

Atoms 28

Atomic Mass, Abundance and Atomic Weight

Isotope atomicmass Abundance atomicmass*abundance

1H 1.00782503 0.99985 1.0076742H 2.014102 0.000148 0.0002983H 3.016049 Trace

---- +________

Atomic weight for H = 1.007674 + 0.00298 = 1.007972

Practice the evaluation of atomic weight of an element using the same method as this example shows.

Atoms 29

Notations for Nuclides

How isotope differ from nuclide?

How are nuclides represented?

3T1 3He2 12C6 16O8

235U92 238U92 234U92

239Pu94

256Fm100

Representations of a nuclide

MEZ

zEM

MzE

Atoms 30

The Quarks

Based on the properties and relationships of particles known in 1962, Gell-Mann in the US and Y. Neémen of Israel predicted the existence and properties of some unknown particles in considerable detail. Gell-Mann and Zweig from Caltech suggested that some heavy particles such as protons and neutrons (called baryons) were made up from three entities called quarks, so named by Murray Gell-Mann after a quote "three quarks for muster Mark, sure he hasn't got much of a bark, etc..." from the novel Finnegan's Mark. J. Joyce, author of the novel, used quarks to rhyme with Mark, bark, lark etc....

Atoms 31

The Standard Model

A Simplified Universe

Generation First Second Third

Quarks u, d c, s t, b

Leptons e, e

Scientific progress often involves establishing conventional wisdom. Other times, it is more a matter of defying it.

Atoms 32

X-ray and Neutrons in the News

X-Ray Optical Systems, Inc., used the ATP funding to develop processes to fabricate and predict the performance of new “capillary optics” technology, which can bend and focus both X-rays and neutrons. Follow-on efforts to develop medical, industrial, and scientific applications are beginning to pay off for both the company and the nation. For example:

• An instrument that generates beams with 100 times the intensity of other compact X-ray sources is an early spin-off of the project.

• The new optics can identify and analyze the structure of proteins four to 10 times faster than conventional methods, a benefit in drug design.

• Among industrial applications, the new optics offer a four- to 16-fold increase in X-ray intensity that is accelerating the development and monitoring of magnetic data-storage materials.

And this is only the beginning.“We have more active collaborations than we have employees, and we have identified more application areas than we have employees ... it’s an exciting time,” says David Gibson, the company president.