Transcript Atomictheory

Introducing Atoms
Atomic Models
• The Greeks were the first people to
think about the nature of matter.
• Democritus proposed the idea that
matter is formed of small pieces that
could not be cut into smaller parts.
• Atomos (uncuttable) or Atoms is what
he came up with.
John Dalton
• John Dalton: an English chemist,
inferred that atoms had certain
characteristics.
• He came up with the Atomic Theory
Atomic Theory
• All elements are composed of atoms that
cannot be divided.
• All atoms of the same element are exactly
alike and have the same mass. Atoms of
different elements are different and have
different masses.
• An atom of one element cannot be changed
into an atom of different elements. Atoms
cannot be created or destroyed in any
chemical change, only rearranged.
Atomic Theory
• Every compound is composed of atoms
of different elements, combined in a
specific ratio.
JJ Thomson (1897)
• Found that atoms contain negatively
charged particles.
• Scientists knew that atoms themselves
had no electrical charge.
• So, Thomas reasoned that atoms must
also contain a positive charge.
• Discovered the electron (-) f-3 P. 103
Earnest Rutherford (1911)
• He was a student of JJ Thomas.
• Found evidence that countered
Thomson’s model.
• Said that an atoms positive (+) charge
must be clustered in a tiny region in the
center called the nucleus.
• Protons contain a positive (+) charge
Bohr’s Model (1913)
• Student of both Thomson and
Rutherford.
• His model said that electrons could
have specific amounts of energy,
leading them to move in certain orbits.
• Resemble the solar system.
Cloud of Electrons
• In the 1920’s the atomic model changed
again.
• Scientists determined that electrons do not
orbit the the nucleus like a planet.
• Electrons can be found anywhere in a cloud
like region around the nucleus.
• An electrons movement is related to its
energy level- specific amount of energy it
has.