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Discovering Atomic Structure. Chapter 3-1. Early Models of the Atom. Cut a piece of Al foil in ½ again and again……. 450BC Democritus , Atomos The ATOM: Smallest piece of an element that retains identity of that element. But what holds them together?. Lavoisier – Conservation of matter . - PowerPoint PPT Presentation
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Discovering Atomic Discovering Atomic StructureStructure
Chapter 3-1Chapter 3-1
Early Models of the AtomEarly Models of the Atom
• Cut a piece of Al foil in ½ again and again…….
• 450BC Democritus , Atomos
• The ATOM: Smallest piece of an element that retains identity of that element.
• But what holds them together?
• Lavoisier – Conservation of matter.• Proust – Law of constant composition
(compounds always have the same proportions of the elements comprising it).–Ex. Water 88.9% O and 11.1% H.
• Dalton’s Atomic Theory:–Extremely small particles (atoms).–Atoms of a given element are identical
but different from all other elements.–Atoms never created nor destroyed.–compounds always have the same
proportions of the elements comprising it
• Recent advances (the scanning-tunneling microscope) have almost allowed us to “see” atoms. Daltons postulates have been proven as fact.
Scanning tunneling microscopeScanning tunneling microscope
• John Dalton had believed atoms to be hard spheres like marbles.
• 1839 – Faraday suggested electrical phenomena related to atomic structure.
• Elektron (amber), static (stationary) electricity.
• Ben Franklin. 2 types of charge, + or - .–Opposites attract, like charges repel.
• So, a + and a + do what?• REPEL
• So, a - and a - do what?
• REPEL
• So, a + and a - do what?
• ATTRACT
• But what about a – and a + ??????
• ATTRACT
Cathode Ray Tube – gave us Cathode Ray Tube – gave us an understanding of electronsan understanding of electrons
Cathode Ray Tubes (contd.)Cathode Ray Tubes (contd.)• The tubes would glow when the end
screen was coated with some substances
• The ‘cathode rays’ could spin a paddle wheel so they must have had mass (particles)
• A magnet deflects the particles just like negatively charged objects
• Thompson was able to use magnets to deflect the cathode rays. He called the particles electrons.
• He could calculate the ratio of Electron ChargeElectron Mass
• Millikan measured the Electron charge.• Solving, the electron mass was found to be
1/1800 mass of a hydrogen atom.• At this time most believed in the “plum
pudding” model of the atom
• RADIOACTIVITY: (led to understanding of nucleus)
• Bequerel had some mysteriously exposed photographic plates. Uranium- radioactive
• Curies isolated Radium and Polonium• Rutherford – radioactive substances show
changes in their properties with time.• His experiment showed + alpha particles,
- beta particles and uncharged Gamma radiation
• Thompson showed that most atoms are neither net (+) or (–)
• But (–) electrons must imply a positive part of the atom , the nucleus
• The further gold foil experiment proved the true nature of atoms.
Rutherford gold foil experimentRutherford gold foil experiment• http://www.mhhe.com/physsci/chemistry/essent
ialchemistry/flash/ruther14.swf
• A very small, dense core (nucleus) containing + charged “protons” and uncharged neutrons
• A lot of space in which electrons traveled – the electron cloud, surrounds the nucleus.