Atomic Structure Teaching Resources

Eric Grunden Raleigh Charter High School Raleigh, NC

What’s Important?

• • • Chemistry EOC (not that this matters anymore…) 2.01 Analyze the historical development of the current atomic theory.

– Early contributions: Democritus and Dalton.

– The discovery of the electron: Thomson and Millikan.

– The discovery of the nucleus, proton and neutron: Rutherford and Chadwick.

– The Bohr model.

– The quantum mechanical model.

2.02 Examine the nature of atomic structure.

– Subatomic particles: protons, neutrons, and electrons.

– Mass number.

– Atomic number.

– Isotopes.

What’s Important?

• AP Chemistry 1. Evidence for the atomic theory 2. Atomic masses; determination by chemical and physical means 3. Atomic number and mass number; isotopes 4. Electron energy levels: atomic spectra, quantum numbers, atomic orbitals 5. Periodic relationships including, for example, atomic radii, ionization energies, electron affinities, oxidation states

My Model

The Atom •Atomism –Pre-socratics/Aristotle •Dalton –The “modern” atomic theory •Thomson –electron/plum pudding model •Becquerel/Curie/radioactivity •Rutherford –Nucleus/Gold Foil experiment •Millikan –q e /”oil drop” experiment •Nuclear transformations –Rutherford again (transmutations) –Decay modes The Electron •Light as a wave •Kirchoff/Bunsen –Emission spectra •Balmer/Rydberg •Planck –Development of quantum concept –Blackbody emitters –“ultraviolet catastrophe”* •Bohr Model •Schrödinger Model –Electron configurations –orbital diagrams

The Atom

• Primary Documents – Dalton reading • Simulations – Gold Foil Experiment standalone/web) (requires Java – • The APE MAN!

– A tomic Number = P rotons = E lectrons – M ass Number = A tomic Number + N eutrons

Primary Documents!

• Be the envy of your Social Science colleagues!

– Dalton’s

A New System of Chemical Philosophy

(suitable for moderate readers) – Bohr’s

On the Constitutions of Atoms and Molecules

(very readable, though complex; complete with math for the truly adventurous) – Others available by search or from the Chemteam website .

• • • Excerpting is the way to go Pair students and have them explain passages to each other Scalable up to more advanced students

The Electron

• Challenging Concepts!

– Revolutionary period – not “normal science” – Highly abstract nature – Cognitive dissonance is good!

• History of Light and electrons are intertwined…

Light theory

Faraday suggests electricity and magnetism related Newton proposes particle theory of light Hooke proposes wave theory Huyghens’ Principle supports waves Young: 2-slit experiment shows wave behavior Maxwell’s Equations relate light, electricity, magnetism Hertz detects radio waves (supports wave theory) Photoelectric Effect (supports particle interpretation – Einstein relates to Planck’s quanta concept) De Broglie proposes matter has wave like qualities

Planck puts idea in Einstein’s head

1600 1700 1800 1900 1915 1930 Thomson (JJ) discovers electron Balmer, Rydberg relate emission spectrum lines to counting number “n”

Bohr Model proposed

Heisenberg Uncertainty Principle

Electron Theory Schr ödinger Wave Model

Pauli Davisson/G.P. Thomson (irony!): electron diffraction Exclusion Principle

Content Highlights

• Observation of spectra without explanation (Kirchoff/Bunsen) • Balmer/Rydberg develop a mathematical relationship without an explanation • Quantization of energy required as a concept

Quantum Mythbusting

• There was no “ultraviolet catastrophe” – Term not coined until 1911 – There was a disagreement between theory and observation, but no catastrophe • Planck did not quantize light – Einstein did this later

Content Highlights, con’t

• Wave-Particle Duality – Einstein suggests that photoelectric effect results can only be explained if light behaves like a particle • Quantum Indeterminacy – Objects exist in

indetermined states

until observed – Schrödinger’s Cat – Ghostbusters

Choose The Form!

Content Highlights, further!

• Hund’s Rule = Monopoly houses • Balmer/Rydberg develop a mathematical relationship without an explanation • Quantization of energy required as a concept

Simulations

Bohr Model Applet (web) Electron Model Comparison (requires Java –standalone/web) Orbital Viewer (standalone, downloadable)

Labs

• Hydrogen Spectrum Lab (h/t Mike Jones, Pisgah HS) • Flame Tests – DON’T use petri dishes, spray bottles, dry salts (safety/toxicity concerns) – Try instead • Wooden splints (steal from coffee shops); soak in • Aqueous solutions of salts (plus a little MeOH): LiCl, KCl (if you have cobalt glasses), CaCl boric acid (for green; I avoid Ba salts) 2, SrCl 2, – Fireworks glasses (rainbow glasses)

The Atomic Theory Org Chart

It’s not just what you know, but apparently whom

Robert Millikan Copenhagen JJ Thomson Cambridge Max Born Niels Bohr Ernest Rutherford Manchester Henry Moseley James Chadwick Hans Geiger Ernest Marsden Friedrich Hund Wolfgang Pauli Göttingen Werner Heisenberg Louis de Broglie Albert Einstein Philipp Lenard Max Planck Berlin Erwin Schr ödinger

Resources

Powerpoint presentations: • Early Atomic Structure •The Bohr Model •The Schrödinger Model (quantum numbers by element)