Transcript atomic theory1

Atomic Model
Development
Rev 6/7/06
Democritus – 400 BC
Defined an Atom as the smallest unit of a
material that can not be split up
Greek word “atom”
means invisible
Atoms are solid,
homogeneous,
indestructible and indivisible
Dalton’s Atom - 1807
Atom = Solid sphere
All elements are composed of tiny invisible
particles called atoms
Atoms of same element- alike &
different from atoms of other
elements
Atoms join together in whole number
ratios to form compounds..that means
they join in a definate proportion every time the
same compound is formed.
Henri Becquerel 1896


Discovered radioactivity
Radiation produced spontaneously
by unstable atomic nucleus
Thomson’s Atom - 1897
Discovered electrons
Plum Pudding model
(for us Americans it looks like a chocolate chip cookie model)
+ charge
“pudding”
Electrons
- charge
Rutherford’s Atom - 1909
discovered dense positively
charged nucleus using gold foil
experiment
electrons
protons
Gold Foil Animation
James Chadwick 1932
•Identified neutron
•Same mass as proton
•No charge
Bohr’s atom - 1913
electrons orbit in energy levels around
the protons in the nucleus.
p+
like our solar system…
(electrons the planets, the nucleus the sun!)
Atomic Time Line
review…