Unit 3: Structure and PropertiesLesson 1: Atomic Structure
Scientist Contribution to Atomic Theory Experiment
Atomic Structure
Chemistry 12: Chapter 4
Atomic StructureYou should be able to:
•Discuss the development of the atom from earliest atomic theory to modern day theory of the atom
•Explain how experimental observations and inferences by Rutherford and Bohr contributed to the development of the planetary model of the hydrogen atom.
•Use appropriate terminology related to atomic structure including orbital, emission spectrum, energy level, photon etc
•Describe the electron configurations of elements, using the concept of energy levels in shells and subshells, the Pauli exclusion principle, Hund’s rule and the aufbau principle.
•Draw energy level diagrams for element and ions.
•Write the electron configuration of any element or ion and to relate its electron configuration to its position in the periodic table.
•Know what each of the four quantum numbers n, l, m, and ms represents.
•Identify the four quantum numbers for an electron in an atom.
•Identify the number and location of the valence electrons in an atom.
•Identify the characteristic properties of elements in each of the s,p and d blocks of the periodic table.
The Hellenic Market
Fire Water Earth Air~~
Greek Model
• Greek philosopher – “thought” experiments
• Idea of ‘atomos’Atomos = ‘indivisible’
• Tear up a piece of matter until you reach the atomos. Democritus’s model of atom
Democritus (400 B.C.)
“To understand the very large,
we must understand the very small.”
”Nothing exists but atoms and space, all else is opinion”.
Alchemy(500 – 1400 A.D.)
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GOLD SILVER COPPER IRON SAND
Alchemical symbols for substances…
transmutation: changing one substance into another
In ordinary chemistry, we cannot transmute elements.
D
Contributionsof alchemists:
Information about elements - the elements mercury, sulfur, and antimony were discovered- properties of some elements
Develop lab apparatus / procedures / experimental techniques - alchemists learned how to prepare acids. - developed several alloys - new glassware
Dalton’s Atomic Theory 1805
1. All matter consists of tiny particles called atoms.
2. Atoms cannot be subdivided, created or destroyed.
3. All atoms of an element are identical.
4. Atoms of different elements are different from each other.
5. Atoms of different types combine is specific ratios to form compounds.
Billiard Ball Model
Radioactivity (1896)1. rays or particles produced by
unstable nuclei
a. Alpha Rays – helium nucleus b. Beta Part. – high speed electronc. Gamma ray – high energy x-ray
2. Discovered by Becquerel – exposed photographic film
3. Further work by Curies
Antoine-Henri Becquerel (1852 - 1908)
Thomson’s Experiment1897
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metal disks
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Thomson’s Experiment
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vacuum tube
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Thomson’s Experiment
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Passing an electric current makes a beam appear to move from the negative to the positive end
Thomson’s Experiment
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Thomson’s Experiment
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By adding an electric field…he found that the moving pieces were negative.
Thomson’s Raisin Bun Model1897
• Using cathode ray tubes, he was able to deflect cathode rays with an electric field.
• The rays are bent towards the positive pole, indicating that cathode ray particles are negatively charged. (electrons)
• Atom is a + sphere with – electrons embedded.
Thomson’s Plum-Pudding or Raisin Bun Model
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 56
Ernest Rutherford (1871-1937)Planetary Model of the Atom
• Learned physics in J.J. Thomson’ lab.
• Noticed that ‘alpha’ particles were sometimes deflected by something in the air.
• Gold-foil experiment
Rutherford
PAPER
Rutherford
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Animation by Raymond Chang – All rights reserved.
Rutherford’s Apparatus
beam of alpha particles
radioactive substance
gold foil
circular ZnS - coatedfluorescent screen
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 120
Rutherford received the 1908 Nobel Prize in Chemistry for his pioneering work in nuclear chemistry.
Results of foil experiment if plum-pudding had been correct.
Electrons scatteredthroughout positive
charges
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 57
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What he expected…
What he got…richochetingalpha particles
Rutherford’sGold Foil Experiment (1909)
Revised Theory
Interpreting the Observed Deflections
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 120
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gold foil
deflected particle
undeflected particles
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Rutherford’sGold-Leaf Experiment
Conclusions:
Atom is mostly empty space
Atom has a very small, dense,positively charged core.(nucleus)
Electrons float around nucleus
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 120
Evidence for Particles
In 1886, Goldstein, using equipment similar to cathode ray tube, discovered particles with charge equal and opposite to that of electron, but much larger mass.
Rutherford later (1911) found these particles to be identical to hydrogen atoms minus one electron
- named these particles protons
Chadwick (1932) discovered particles with similar mass to proton but zero charge.
- discovered neutrons
An unsatisfactory model for the hydrogen atom
According to classical physics, lightshould be emitted as the electron circles the nucleus. A loss of energywould cause the electron to be drawncloser to the nucleus and eventuallyspiral into it.
Hill, Petrucci, General Chemistry An Integrated Approach 2nd Edition, page 294
Bohr’s Model
Nucleus
Electron
Orbit
Energy Levels
Niels Bohr (1913)1. e- can only occupy certain
regions of space (orbits)2. e- only have specific
(quantized) energy values in an atom (energy levels)
3. e- can move from one orbit to another by absorbing or emitting energy, giving rise to characteristic spectra.
Bohr’s model could not explain the spectra of atoms heavier
than hydrogen.
Bohr Model of Atom
The Bohr model of the atom, like many ideas in the history of science, was at first prompted by and later partially disproved by experimentation.
http://en.wikipedia.org/wiki/Category:Chemistry
Increasing energyof orbits
n = 1
n = 2
n = 3
A photon is emittedwith energy E = hf
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