Transcript The Atomic Theory of Matter

The Atomic Theory of Matter
By Shaffer Lisle
The First Theories
• John Dalton’s proposed theories:
• Each element is composed of particles called
atoms.
• All atoms in an element have identical mass and
other properties. Atoms of one element are
different from that of another element.
• Atoms are not changed into atoms of a different
element by chemical reactions; they are neither
changed nor destroyed during chemical
reactions.
John Dalton’s Theory and Its
Change
• John Dalton’s theory says that atoms are
the smallest particles that still retain
chemical identity of an element.
• With new technology we have found
subatomic particles within atoms.
• A lot of things are still considered correct
with John Dalton’s theory even today.
The Discovery of the Electron
• The electron was found when scientists
started to study cathode ray tubes.
• Cathode ray tube: pumped almost empty
of air (vacuum tube).
• A high voltage produces radiation within
the tube. The radiation is known as
cathode rays because it comes from the
negative electrode or cathode.
The Discovery of the Electron
• There were conflicting views about cathode rays.
It wasn’t clear whether they were a stream of
particles or a form of radiation. Experiments
showed that they were deflected by electric or
magnetic fields in a consistent way of their being
a stream of negative charge. The British
Scientists J.J. Thomson observed that the rays
stayed the same regardless of the cathode
material. His discoveries were considered the
discovery of the electron.
Subatomic Particles
• The rest of the subatomic particles were found when
scientists made theories on where the electrons were in
an atom. In 1910, a scientist named Rutherford
examined the effects of passing alpha rays through a
gold foil a few thousand atoms thick. He found that most
passed right through the gold foil while some were
deflected. This was later concluded that there is a lot of
empty space in an atom and that they mostly passed
through the empty space ,sometimes getting deflected
by the later discovered nucleus (made up of protons and
neutrons).
The Modern Atomic Structure
• The modern atomic
structure is mainly the
protons and neutrons
in the nucleus, with
electrons moving in
the open space in the
atom.
Atoms
Neutrons-neutral
Protons-positive
Electron-negative