Atoms1 tiny wonders worth studying Energy states of electrons in atoms are represented by this...
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Transcript of Atoms1 tiny wonders worth studying Energy states of electrons in atoms are represented by this...
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.