Download atomic models oct 29th

The First Atomic Theory- John
Dalton
• Began teaching Chemistry at 12!
• English school teacher, but never a
trained chemist
• Used the laws to prove that atoms existed by making
meticulous notes. He kept a diary with
200,000 scientific entries!
• Many of his unpublished documents were
destroyed by the bombing of England in
WWII- “War does not only kill the living.”Asimov
Dalton’s Atomic Theory- 5
Postulates
1. All matter is composed of extremely small, indivisible
particles called atoms.
2. Atoms of the same element are identical to each other
and have the same properties.
3. Atoms of different elements have different properties.
4. Atoms of different elements combine in whole-number
ratios to form compounds.
5. In chemical reactions, atoms are combined, separated,
and rearranged but never created or destroyed.
We know now…
• Atoms can be divided into smaller parts called
electrons, protons, and neutrons
• Atom of one element can change into another
element- creating a new atom (nuclear energy)
• Atoms of the same element can have different
properties
isotopes- an atom of the same element, with a
different # of neutrons
Ex: C12 C13 C14
What Dalton’s Atom looks like
• A solid sphere- no electrons, neutrons, or
protons, because he believed it was
indivisible
The Indivisible, Solid Sphere Model
(1808)
• This Model was the
first model of what
was once believed
to be the look,
shape, and form of
an atom.
• This model was
created by John
Dalton.
The Cathode Ray Tube Experiment
• 1897: The cathode
ray tube experiment
• Done by J.J.
Thomson- also an
Englishman and
colleague of Dalton
• Discovery of
Electrons
Cathode Ray Tube (J. J.
Thomson)
The Plum-pudding Model
(1904)
• This was the
next model to
come after John
Dalton’s model
of the atom.
• This model was
created by J.J
Thomson.
• Rutherford in 1901 created the
first human “nuclear reaction”
– led to the discovery of the
proton
James Chadwick- discovered
the neutron
Niels Bohr- created a stable,
quantum version of
Rutherford’s atomic model
(energy levels)
1909 Rutherford’s Gold Foil
Experiment
Rutherford’s Atomic Model
• Electrons are less
heavy than protons or
neutrons and
electrons orbit around
the nucleus- like the
planets orbit the sun
• The nucleus is
positively charged
and contains protons
and neutrons
• The electron orbits
are not defined- they
can be anywhere
Rutherford Nuclear Atom Model
(1911)
• This was the next
model to come
after J.J
Thomson’s version
of the atom.
• This model was
created by Ernest
Rutherford.
The models we have seen so far
Dalton’s
Atomic model
Think of as many words as you can relating
these models
• Atomic number= # of protons
Neutral atom has the same number of electrons
as protons
• Mass number = # protons and neutrons;
different for different isotopes
• Atomic Mass / Atomic Weight= average atomic
mass of all isotopes of the element
• Rutherford’s model is
inherently unstable
• If the electron can
orbit at any distance
from the nucleus, the
atom would collapse
in on itself!!!
The Bohr Model
• Niels Bohr determined
that there are discrete
(fixed) energy levels in
an atom
• The Bohr model stabilizes
Rutherford’s model
• In Bohr’s model, the
electrons in the farthest
orbit are the highest
energy level; electrons in
the closest orbit are in the
lowest energy level
Bohr’s Energy Levels
• Electron Energy Level spacings are
affected by nearness to the nucleus
Planetary System Model
(1913)
• This was the next
model to come
after Rutherford’s
version of the
atom.
• This model was
created by Neils
Bohr.
What we think an atom looks like
• Orbitals = region where
the electron is, we don’t
know exactly where, but
we know it is in this
general region
• Nucleus= where the
protons and neutrons are
• Energy Levels= discrete
and increase as the
electron goes farther from
the nucleus
Electron Cloud Model
(1900’s but after 1913)
• This was the next
model to come
after Bohr’s version
of the atom.
• This model was
created by Erwin
Schroedinger.