Chapter 4.1 and 4.3 Notes

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• Chapter 4.1 and 4.3 Notes
• Studying Atoms
• Democritus (460 -370 B.C.) was a Greek
  philosopher that used the word atoms to describe
  extremely small particles that could not be
  divided.
• Daltons atomic theory - (1766-1844) All matter
  is made up of individual particles called atoms,
  which can not be divided.

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• Main Points of Daltons theory
• 1. All elements are composed of atoms
• 2. All atoms of the same element have the same
  mass, and atoms of different elements have
  different masses.
• Compounds contain atoms of more than one
  element.
• In a particular compound, atoms of different
  elements always combine in the same way.

You must know this for the test!
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• Not all of Daltons ideas were completely
  correct.
• He thought atoms were tiny solid spheres.
• Later scientists had to revise Daltons theory
  based on new evidence

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• Thomsons Model of the Atom
• A physicist named Thomson (1856-1940) used
  electric current to learn more about atoms.
• Thomsons experiments provided the first
  evidence that atoms are made up of even smaller
  particles.

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• Thomson revised Daltons theory and Thomsons
  model is called the plum pudding model.

• Thomsons model showed that negative charges were
  evenly scattered throughout an atom filled with
  positive charged mass of matter. So he discovered
  the electron.

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Thomsons Experiment

• Made a piece of equipment called a cathode ray
  tube.

• It is a vacuum tube - all the air has been pumped
  out

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Vacuum tube
Metal Disks
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• Passing an electric current makes a beam appear
  to move from the negative to the positive end

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• By adding an electric field he found that the
  moving pieces were negative (notice the
  attraction of the beam to the positive pole).

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• Rutherfords Atomic Theory
• Rutherford in 1911 discovered positive charged
  particles and called them alpha particles.

• Rutherford conducted experiments and determined
  that the positive charged particles were located
  at the center of an atom. He called it the
  nucleus.

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• Rutherfords model says that all of an atoms
  positive charge are concentrated in its nucleus.
  This revised Thomsons model.

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BOHR'S MODEL OF THE ATOM
In 1913, the Danish scientist Niels Bohr
suggested that electrons in an atom move in a
fixed orbit and constant speed around the nucleus
much like that of the solar system.
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Bohrs Atomic Model
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Energy Levels

• An electron in an atom can move from one energy
  level to another when the atom gains or loses
  energy.

• The movement of electrons between energy levels
  explains the light you see when fireworks
  explode. The heat (energy) from the explosion
  causes some electrons to move to a higher energy
  level (excited state). When the electrons move
  back to their lower energy level they release
  energy in the form of visible light.

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Energy Levels

• The most stable electron configuration (how the
  electrons are arranged) is when the electrons are
  in their lowest energy levels.
• When all the electrons for an atom are in their
  lowest energy levels the atom is in the ground
  state.

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Modern Model of the Atom The electron cloud

• Spherical cloud of varying density

• Varying density shows where an electron is more
  or less likely to be

So, basicallyNOW we know that electrons do HANG
out in a cloudlike formation outside of the
nucleus. Patterns can be somewhat predictable
but are NOT FIXED.
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Sizing up the Atom
Despite their size, we CAN see atoms with an
electron scanning tunneling microscope. A pure
copper (Cu) coin contains 2.4 x 1022 atoms!!!!
That 24,000,000,000,000,000,000,000 ATOMS!!!!
A line of 100,000,000 copper atoms side by side
would only be 1 cm long!