1. Structure of the Atom

2. To be able to understand and change matter we need to know what matter is made of (Composition) and How it is put together (Structure).

3. Put yourself in the shoes of early scientists
So what is matter?
Put yourself in the shoes of early scientists

4. ~ 400 BCE Democritus proposes the atom
“Nothing exists but atoms and empty space, everything else is opinion.”

5. Alchemy becomes Chemistry and the Idea of the Atom is Reborn
Around 1800, Lavosier realized that to advance chemistry mathematics and the concept of the atom would be needed.

6. The Rediscovery of the Atom & Injection of Math Lead to
Law of Conservation of Matter - Atoms are not created or destroyed. Conservation Law depended on a theory of gasses.
Relative weights of elements - Avogadro
Law of Constant Composition - Compounds are made up of exact ratios of atoms.

7.  Dalton's Atomic Theory
Elements are made of extremely small particles called atoms.
Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
Atoms cannot be subdivided, created, or destroyed.
Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
In chemical reactions, atoms are combined, separated, or rearranged.

8. Electrical Nature of the Atom
Franklin discovers charges which he calls positive and negative. He believes that these two charges are cloud-like fields have opposite natures.
FARADAY describes the atom as being made of these charges

9. Thomson discovers that the negative charge is a subatomic particle.

10. Thomson’s Cathode Ray Tube Experiments

12. Rutherford’s Alpha Scattering Experiment
Shoots radioactive particles at a very thin gold foil.
Wants to know if the radioactive particles will be deflected.

13. Rutherford expects the radioactive particles to pass thru the gold foil without much resistance because the radioactive particles are small & the atom is basically a positive charge cloud with very small negative particles.

15. Rutherford’s Atom

16. ATOMIC NUMBER Moseley around 1913 discovered a unique positive charge on nucleus which starts to explain why element behaves differently.   The number of protons in the nucleus is called “atomic number”.

17. Spectrometer

18. Discovery of Particles of Light
Ejection of electrons depended on Frequency first. After minimum frequency to eject particles was achieved, increasing brightness ejected more particles.
Discovery of Particles of Light
PHOTONS

19. Bohr was trying to figure out why different elements will give off different colors when placed into a flame.

20. Bohr’s Model Electrons are in orbitals
Each “orbital” has a unique energy.
Electrons can move between orbitals by absorbing or releasing energy. When electrons release energy it is always in the form of electromagnetic radiation (packets of light).
Light
Metallurgists

23. Other Uses for Emission Spectra
Composition of the stars
Metallurgists and Chemists use spectroscopy to identify elements within a substance

24. James Chadwick discovers the NEUTRON allowing for a later
Neutrons add to the atom’s mass
Neutron exert the strong force which keeps protons together

25. Character of Subatomic Particles
Robert Millikan is important for the discovery of the size of electron

26. Contemporary Model of the Atom
Nucleus can be changed
Radioactivity
Atoms can be split apart (Fission)
Larger atoms can be made from smaller atoms (Fusion)
E = MC2

27. Electron clouds based on probability an electron exists in a certain region of space around the atom

28. 9/17/2004 ORNL Electron Microscope Images (0
9/17/2004 ORNL Electron Microscope Images (0.6 angstroms resolution or meters) of Silicon Crystal
Dumbbell-shaped electron clouds!!!

29. Scanning Tunneling Microscope

31. Protons & neutrons are not fundamental.
Protons and neutrons are made of Quarks

32. END

33. Answer these questions
Draw an atom
Include subatomic particles, charges, size and locations
Answer these questions
What makes elements different?
Define atoms, elements, compounds, mixtures, ions, isotopes?