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Atoms: Development of the Atomic Theory

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Atoms: Development of the Atomic Theory Democritus 460 BC - Greek philosopher proposes the existence of the atom He pounded materials until he made them into smaller ... – PowerPoint PPT presentation

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Title: Atoms: Development of the Atomic Theory


1
AtomsDevelopment of the Atomic Theory
2
Democritus
  • 460 BC - Greek philosopher proposes the existence
    of the atom
  • He pounded materials until he made them into
    smaller and smaller parts
  • He called them atoma which is Greek for
    indivisible.

3
Democritus
  • His Theory
  • All atoms
  • Are small hard particles
  • Are made of a single material formed into
    different shapes and sizes
  • Are always moving, and they form different
    materials by joining together

4
John Dalton
  • 1803 - British chemist elements combine in
    specific proportions to form compounds

Solid Sphere Model or Bowling Ball Model Proposed
by John Dalton
5
John Dalton
  • His Theory
  • All substances are made of atoms that cannot be
    created, divided, or destroyed.
  • Atoms join with other atoms to make new
    substances.
  • Atoms of the same element are exactly alike, and
    atoms of different elements are different in mass
    and size.

6
J.J. Thomson
  • 1897 - English chemist and physicist discovered
    1st subatomic particles

Plum Pudding Model or Raisin Bun Model Proposed
by J.J. Thomson
7
J.J. Thomson
  • His Theory
  • Atoms contain negatively charged particles called
    electrons and positively charged matter.
  • Created a model to describe the atom as a sphere
    filled with positive matter with negative
    particles mixed in
  • Referred to it as the plum pudding model

8
Ernest Rutherford
  • 1912 - New Zealand physicist discovered the
    nucleus

Nuclear Model Proposed by Ernest Rutherford
9
Ernest Rutherford
  • His Theory
  • Small, dense, positively charged particle present
    in nucleus called a proton
  • Electrons travel around the nucleus, but their
    exact places cannot be described.

10
Niels Bohr
  • 1913 - Danish physicist discovered energy levels

Bohr Model or Planetary Model Proposed by Niels
Bohr
11
Niels Bohr
  • His Theory
  • Electrons travel around the nucleus in definite
    paths and fixed distances.
  • Electrons can jump from one level to a path in
    another level.

12
Erwin Shrodinger
  • 1924 - Austrian physicist developed the electron
    cloud model

Electron Cloud Model Proposed by Erwin
Schrodinger
13
Erwin Shrodinger
  • His Theory
  • The exact path of electrons cannot be predicted.
  • The region referred to as the electron cloud, is
    an area where electrons can likely be found.

14
James Chadwick
  • 1932 - English physicist discovered neutrons
  • His Theory
  • Neutrons have no electrical charge.
  • Neutrons have a mass nearly equal to the mass of
    a proton.
  • Unit of measurement for subatomic particles is
    the atomic mass unit (amu).

15
Modern Theory of the Atom
  • Atoms are composed of three main subatomic
    particles the electron, proton, and neutron.
  • Most of the mass of the atom is concentrated in
    the nucleus of the atom.

16
Modern Theory of the Atom
  • The protons and neutrons are located within the
    nucleus, while the electrons exist outside of the
    nucleus.
  • In stable atoms, the number of protons is equal
    to the number of electrons.

17
Modern Theory of the Atom
  • The type of atom is determined by the number of
    protons it has.
  • The number of protons in an atom is equal to the
    atomic number.

18
Modern Theory of the Atom
  • The sum of the number of protons and neutrons in
    a particular atom is called the atomic mass.
  • Valence electrons are the outermost electrons.
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