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The Atom

The Atom. Lecture 1. Atomic Structure & Its History. Much of what we know about atomic structure today is the result of indirect observation of atoms and the particles of which they are composed. Atomic Structure & Its History.

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The Atom

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  1. The Atom Lecture 1

  2. Atomic Structure & Its History • Much of what we know aboutatomic structuretoday is the result of indirect observationof atoms and the particles of which they are composed

  3. Atomic Structure & Its History • Over 2,300 years ago, the Greek philosopher Democritus was the first to propose that matter was composed of atoms

  4. Atomic Structure & Its History • Democritus believed that - • everything is composed of "atoms", which are physically, but not geometrically, indivisible • that between atoms, there lies empty space • that atoms are indestructible • that atoms have always been, and always will be, in motion • that there are an infinite number of atoms, and kinds of atoms, which differ in shape, and size

  5. Atomic Structure & Its History • He was correct in one part: • the forces that hold together the nucleus of an atom are the most powerful in the universe, making atoms indivisible in all but extremely powerful reactions

  6. Atomic Structure & Its History • Those reactions are called fission • Fission is when the nucleus of an atom is split apart • When this occurs tremendous energy is released

  7. Atomic Structure & Its History • Nuclear weapons are an example of this incredible force • Direct observation of atomic structure is all but impossible • Scientists have relied on models to represent the structure of atoms

  8. The Dalton Model: 1803 • English chemist John Dalton developed the first atomic model in 1803 • He saw atoms as indestructible, indivisible and spherical

  9. The Dalton Model: 1803 • His theories were based on what had been observed in chemical reactions and was widely accepted until the development of the Crooks tube

  10. The Crooks Tube • In 1897, English scientist JJ Thomson noticed that a stream of negatively charged particles would flow through a special tube, called a Crooks tube, no matter what gas was used • Thomson theorized that negatively charged particles were present in the atoms of all elements

  11. The Crooks Tube • His final theory was that atoms were made up of positively and negatively charged particles evenly distributed and that the atom was a solid mass • He is credited with the identification and discovery of the electron

  12. The Crooks Tube • https://www.youtube.com/watch?v=XU8nMKkzbT8

  13. The Rutherford Model: 1909 • British physicist Lord Rutherford’s experiments in 1909 indicated that atoms were largely empty space

  14. The Rutherford Model: 1909

  15. The Rutherford Model: 1909

  16. 2. The Rutherford Model https://www.youtube.com/watch?v=5pZj0u_XMbc

  17. The Bohr Model • In 1913, Danish scientist Neils Bohr developed a model of the atom that proposed there existed certain definite orbitsin which electrons traveled • Bohr proposed 7 different levels, or distances that occur around the nucleus

  18. The Bohr Model • Bohr hypothesized that the greater the radius of the level, the greater the energy of the electrons at that level

  19. The Bohr Model • His models suggested that in an atom’s normal state, all electrons are in the lowest energy levels, and because of this cannot move to a lower level • The atom is stableand said to be at its ground level state

  20. 3. The Bohr Model http://mrsgillumscience.com/12Reg_Sci/12chp12/12%20chp12%20ppts/3.%20bohr%20model.mp4

  21. The Excited State • If energy is added to the atom by heat or electrical energy,the absorbed energy can cause one or more of the electrons within the atom to move to ahigher energy level • When this happens the atoms are said to be in an excited state

  22. The Excited State • The atom at the excited state is unstable and makes efforts to return to ground level state • As the electrons return to this level they release energy • The energy given off exactly equals the amount absorbed when the electrons moved to the higher energy levels

  23. The Modern Model of the Atom Charge Cloud Model: • this shows electrons as being part of a diffused cloud of varying densities

  24. Brainpops: Atomic Models • Brainpops

  25. Brainpop quiz How did you do?

  26. 4. A Musical Review https://www.youtube.com/watch?v=vUzTQWn-wfE

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