Transcript Models of the Atom:

Models
of the
Atom:
a
history
The Atom’s History……
Recognized 4 major
elements:
- Fire
- Earth
- Water
- Air
Democritus
(4th century BC)
Greece
 Believed that matter
was composed of
tiny indivisible
particles called
atoms (“indivisible”)
 Based on philosophy
NOT
John Dalton
- Came up with a 5part atomic theory
- Atoms are tiny,
solid, indivisible
spheres of
matter
Dalton’s Atomic Theory
No, you don’t need to write all of this… just FYI
1.
2.
3.
All elements are composed of
submicroscopic, indivisible
particles called atoms
Atoms of the same element
are identical. Atoms of
different elements are not the
same.
Atoms of different elements
can physically mix together or
can chemically combine with
one another in simple wholenumber ratios to form
COMPOUNDS.
Chemical reactions occur when
atoms are separated, joined or
rearranged. Atoms of one
element are never changed into
atoms of another element.
5. Atoms cannot be subdivided,
created or destroyed.
#5 has changed because of the
discovery of the proton,
neutron, and electron
#2 has been modified because of
isotopes.
4.
Dalton’s model

Pros:
– Most of the atomic
theory is still valid
today

Cons:
– Thought atoms
were indivisible (no
p, e, n)
– No mention of ions
or isotopes



Thomson discovered the electron,
realized atoms were not indivisible
Revised atomic model: “plum
pudding model”
A ball of + charge containing a
number of electrons
Thomson model
Pros:
– Explained some
electrical
properties of
atoms
Cons:
– Doesn’t discuss # of
protons or neutrons
– How are earranged?
– How are electrons
stripped to form
ions?
 Dense nucleus of
protons/neutrons - electrons in
empty space around it
Rutherford model
Pros:
– Explains #
protons/neutrons,
arrangement, and
e- stripping
Cons:
– Opposite charged
particles attract each
other, what keeps ein place?
Bohr Model

Electrons in each energy level have a fixed energy quantum
– Quantized energy levels  Fixed amt of energy required to move from 1
energy level to another
 like the rungs of a ladder
– Cons:
 only works perfectly for Hydrogen
Quantum Model
(Current)
Quantum Model
 Describes electrons as waves confined to a
specific shapes (Incorporates the Heisenberg
Uncertainty Principle and the Schrodinger
Wave Equation)
– Energy Levels + S, P, D, and F orbitals for
electrons
– Orbitals – define the shapes where
electrons exist around the nucleus
 Cons: ??? (working pretty good so far!)