1 / 60

Atomic Theory

Atomic Theory. What is it? Who figured it out? When did they do it? How did they do it? Why do we believe it?. What can you tell from this picture?. What is an ATOM?. An atom is the smallest particle of an element that retains the identity of the element. ZZZ ZZZ ZZZ. ATOM.

carly-barton
Download Presentation

Atomic Theory

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Atomic Theory • What is it? • Who figured it out? • When did they do it? • How did they do it? • Why do we believe it?

  2. What can you tell from this picture?

  3. What is an ATOM? • An atom is the smallest particle of an element that retains the identity of the element. ZZZ ZZZ ZZZ

  4. ATOM

  5. Atoms combine to form compounds

  6. Democritus Lived 450 B.C. Proposed that all the stuff in the world is “atomos” Tiny, indivisible particles Aristotle Questioned theory of Democritus Rejected it for lack of proof The Ancient Greeks

  7. Roger Bacon • Lived in 13th century • Believed that science should be based on experimental evidence.

  8. ALCHEMISTS • Tried to turn base metals into precious metals. • Developed knowledge and techniques • Not true scientists

  9. Copper into Gold Laboratory • Alchemists tried to turn normal copper into gold coins! • If they succeeded, they would never need to work!

  10. Prove that the coins are GOLD • How is copper different than gold? • How can you test it? • What techniques are you using…that Democritus did not use?

  11. Antoine Lavoisier • 1743-1794 • French • Father of Chemistry • Sadly, beheaded in French Revolution

  12. Lavoisier • LAW OF CONSERVATION OF MATTER • Matter, like energy, is neither created nor destroyed in a chemical reaction. • This concept established modern chemistry.

  13. What was different? • Experimentation • He used a balance to study the role of oxygen in rusting and burning.

  14. Other people did it, too! • Priestly did similar experiments. • He believed a false theory of Phlogiston. • Kept his mind closed to new idea.

  15. PROUST • 1799 • Law of Constant Composition • A given compound always contains the same elements in the same proportion by mass. WATER 89% Oxygen WATER 11% Hydrogen

  16. JOHN DALTON LAVOISIER PROUST ATOMIC THEORY OF MATTER DEMOCRITUS BACON

  17. DALTON’S ATOMIC THEORY OF MATTER 1. Allmatter is composed of submicroscopic (extremely small) indivisible particles called ATOMS. 2. All atoms of a given element are identical. The atoms of any one element are different from those of any other element.

  18. DALTON’S ATOMIC THEORY OF MATTER 3. Atoms are neither created nor destroyed in a chemical reaction. Chemical reactions occur when atoms are separated, joined, or rearranged. However, atoms of one element are never changed into atoms of another element as a result of a chemical reaction.

  19. DALTON’S ATOMIC THEORY OF MATTER 4. Atoms of different elements can mix physically or can combine chemically with one another in simple whole number ratios to form compounds.

  20. What does this mean? Not perfect... but a workable theory to build on. Atomic Theory of Matter

  21. Scientists had been doing many experiments with electricity since Ben Franklin flew his kite. • Faraday suggested that electricity might explain the atom • English physicist, J.J. Thomson 1856-1940 • Discovered electrons in 1897 • Thomson experimented with a “cathode ray tube”

  22. Cathode Ray Tube

  23. Cathode Ray Tube

  24. Flow of electric current through gases. Sealed gas in glass tube with metal plates at the end. Connected plates to high voltage source: Anode + and Cathode – Thomson’s Cathode Ray Tube Experiment

  25. This ray could be deflected toward a positive charge… It has a negative charge. This ray could move things… It was made of particles of matter. This ray acted the same no matter what materials were used… It was not atoms…it must be part of all atoms

  26. Cathode ray is composed of very small negatively charged particles that are part of atoms ELECTRONS Cathode Ray Tube

  27. Cathode Ray Tube

  28. Diagram of CRT

  29. Atomic Theory • Millikan devised experiments to determine the mass and charge of the electron. • Protons : discovered in 1886 Positively charged particles Also discovered with cathode ray tube…these particles went the other direction.

  30. The Nuclear Atom • Rutherford • Identified three types of radiation • Alpha…positive particle • Beta…negative particle • Gamma…high energy • Devised the GOLD FOIL EXPERIMENT Now…where were we….?

  31. Rutherford’s Nuclear Atom • Most of the mass of an atom is in the center…the nucleus…with electrons moving around it.

  32. Nuclear atom • By 1932, neutron was discovered, too. • The nucleus is the central core of the atom, composed of protons and neutrons. Because, protons and neutrons have much greater mass than electrons, almost all of the mass of the atom is concentrated in a tiny nucleus…a dime in a football stadium!

  33. What next? • We know the parts of the atom. • We know about the nucleus. • What about the electrons? ???????

  34. Bohr’s Model • Light provided the next clues for the structure of the atom

  35. Light has a Dual Nature Like this picture… Young lady or Old lady?

  36. Light is a wave Electromagnetic radiation travels in waves.

  37. As the wavelength increases, the frequency decreases. • The greater the frequency the greater the energy.

  38. Light acts like Particles • Electromagnetic radiation also has the properties of particles. • Bohr suggested that energy is emitted and absorbed in discrete quantities called Quanta or Quantum packets or pieces of energy “Jumps”

  39. Demonstrate Quantum

  40. Dual Nature of Light is the next tool for understanding the atom • Energy is directly proportional to frequency…wave nature. • Einstein proposed that light consists of quanta of energy that behave like particlesof light…he called these photons. • Example: photoelectric effect This is the DUAL NATURE OF LIGHT

  41. Continuous Spectrum vs. Line Spectrum

  42. What does this have to do with ATOMS? • Atoms give off energy as photons of light. • Line spectra of elements reveal that electrons exist in quantized (discrete) energy levels. • Rainbow…continuous spectrum • Line…discontinuous spectrum • The color allows us to calculate the energy • higher frequency = higher energy… • purple higher than red

More Related