HISTORY OF THE ATOM:
JOHN DALTON:1800s
-Suggested that substances were made up from atoms and that atoms were
tiny, hard spheres
-Suggested that each chemical element had its own atoms that differed to
others’ in terms of their mass.
-Believed that atoms could not be divided
-Suggested that in chemical reactions, atoms rearrange themselves and
combine with others in different ways
JJ THOMSON: late 1800s
-Discovered the ELECTRON: a tiny, negatively charged particle that was found
to have a mass of about 2000x smaller than the lightest atom.
-He experimented by applying high voltages to gases at low pressure, and he
did this on beams of particles:
Seeing as they were attracted to positive charge, that meant that they were
negatively charged.
-Suggested that the electrons must be embedded in a cloud of positive charge:
PLUM PUDDING MODEL.
RUTHERFORD/GEIGER & MARSDEN:
-They carried out the ALPHA PARTICLE SCATTERING experiment, where they
fired dense, positively charged particles (called alpha particles) to very thin
gold foil pieces.
-They expected the particles to go straight through the foil, but some repelled
backwards.
-Rutherford said that Thompson’s atom couldn’t be correct and suggested
that the positive charge must be in the middle of the atom-the NUCLEUS.
-He said that the electrons must be orbiting around the NUCLEUS which
contains PROTONS.
NEILS BOHR:1914
-Suggested that the electrons must be orbiting around the nucleus at set
distances in fixed ENERGY LEVELS or SHELLS.
JAMES CHADWICK:1932
-Many scientists at this time suspected a second subatomic particle, which
would explain the missing mass in atoms.
-They suspected a particle with no charge, the NEUTRON.
-In 1932, James Chadwick was finally able to prove the existence of neutrons.
JOHN DALTON:1800s
-Suggested that substances were made up from atoms and that atoms were
tiny, hard spheres
-Suggested that each chemical element had its own atoms that differed to
others’ in terms of their mass.
-Believed that atoms could not be divided
-Suggested that in chemical reactions, atoms rearrange themselves and
combine with others in different ways
JJ THOMSON: late 1800s
-Discovered the ELECTRON: a tiny, negatively charged particle that was found
to have a mass of about 2000x smaller than the lightest atom.
-He experimented by applying high voltages to gases at low pressure, and he
did this on beams of particles:
Seeing as they were attracted to positive charge, that meant that they were
negatively charged.
-Suggested that the electrons must be embedded in a cloud of positive charge:
PLUM PUDDING MODEL.
RUTHERFORD/GEIGER & MARSDEN:
-They carried out the ALPHA PARTICLE SCATTERING experiment, where they
fired dense, positively charged particles (called alpha particles) to very thin
gold foil pieces.
-They expected the particles to go straight through the foil, but some repelled
backwards.
-Rutherford said that Thompson’s atom couldn’t be correct and suggested
that the positive charge must be in the middle of the atom-the NUCLEUS.
-He said that the electrons must be orbiting around the NUCLEUS which
contains PROTONS.
NEILS BOHR:1914
-Suggested that the electrons must be orbiting around the nucleus at set
distances in fixed ENERGY LEVELS or SHELLS.
JAMES CHADWICK:1932
-Many scientists at this time suspected a second subatomic particle, which
would explain the missing mass in atoms.
-They suspected a particle with no charge, the NEUTRON.
-In 1932, James Chadwick was finally able to prove the existence of neutrons.
