Download In 1808, Dalton proposed the first "modern" atomic theory

Atomic Theories
John Dalton
In 1808, Dalton proposed the first
"modern" atomic theory:
O the atom is the smallest particle of
matter.
O atoms cannot be created or
destroyed
O each element has its own kind of
atom.
O compounds are created when
atoms of different elements combine.
He proposed the atom was a solid
sphere that looked like a billiard ball.
Michael
Faraday
- In 1832, Michael Faraday discovered
that atoms can gain electric charges and
form charged atoms called ions
- In this modified version of Dalton’s
model, he said:
1) Matter must contain positive and
negative charges.
2) Opposite charges attract, and like
charges repel.
3) Atoms combine to form the particles
of a compound because of the electrical
attraction between charged atoms.
J.J. Thomson
In 1889, Thomson proposed a model
called the “raisin bun”. It explained
that:
1) Atoms contain particles called
electrons
2) Electrons have a small mass and
negative charge
3) The rest of the atom is a sphere of
positive charge
4) The electrons are embedded in this
sphere, so that the resulting atoms
are neutral, or uncharged.
Nagaoka
In 1904, Nagaoka propsed the
planetary model of the atom. This
modeled the atom as a large positive
sphere surrounded by a ring of
negative electrons.
He did not talk about protons or
neutrons.
Ernest
Rutherford
- In 1911, he tested Thomson’s and Nagaoka’s
models by aiming alpha particles at a thin
sheet of gold foil. He thought the particles
would all pass through but a very small
amount bounced almost straight back.
- To explain his results, he came up with the
nuclear model:
1) An atoms has a tiny, dense, positive core
called the nucleus (which deflected the
alpha particles and contains protons)
2) The nucleus is surrounded mostly by
empty space, containing rapidly moving
negative electrons (through which the
alpha particles passed through).
Niels Bohr
- In 1913, he developed this model to
explain where the electrons go around
the nucleus.
- In his diagrams, the symbol of the
element is written in the center to
represent the nucleus.
- A series of circles is drawn around the
nucleus to represent the orbits, and
electrons are shown in these orbits.
BohrRutherford
Diagrams
- A combination of Rutherford’s nuclear
model with Bohr’s planetary model
- It summarizes the numbers and
positions of all three subatomic particles
in an atom.
- A circle is drawn in the center to
represent the nucleus. The numbers of
protons and neutrons are written in this
circle.
- Electrons are again shown in circular
orbits around the nucleus