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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vacuum tube

metal disks

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Thomson’s Experiment

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vacuum tube

metal disks

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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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