Transcript 2/1: Atomic Structure

Atomic Structure- History
Philosophers and Scientists
• Know how the following contributed to the history
of the atom:
Philosophers from History of the Atom video
– Empedicles - four “elements” – earth, water, fire,
air.
– Leucippus - the first Greek to develop the theory
of atomism — the idea that everything is
composed entirely of various imperishable,
indivisible elements called atoms
– Aristotle - five elements – earth, air, fire, water,
and aether
Next week
Modern Day scientists
– Dalton
• atoms could not be divided
• all elements of a given element are the same
• different atoms could join to form compounds
– Thomson
• the plum pudding model
• negatively-charged "plums” surrounded by
positively-charged "pudding”
– Rutherford
• atom is made up of a central charge
surrounded by a cloud of orbiting electrons
– Bohr
• electrons are in levels around the nucleus
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf
Structure of the Atom
Particle
Charge
Mass
(atomic
mass units)
1
Location
Proton
positive
+
Neutron
neutral
Ø
1
nucleus
Electron
negative
-
0.0006
orbit, level,
cloud
nucleus
The Nucleus
A 1946 test of an atomic bomb in the lagoon at Bikini atoll. The
explosion has just started; surplus ships moored nearby can still be
seen.
http://video.google.com/videosearch?source
id=navclient&rlz=1T4SUNA_enUS316US3
16&q=atomic%20bomb&um=1&hl=en&ie
=UTF-8&sa=N&tab=iv#
http://www.youtube.com/wa
tch?v=bw85r24WW3s
• The nucleus
– the center of the atom composed
of protons and neutrons
– held together by four forces (electromagnetic,
strong , weak, and gravity)
– 99.9% of the atom’s mass is here
– about 100,000 times smaller than
the entire atom
– the atomic number of an atom is the number
of protons in the nucleus
– the atomic mass or mass number of an atom is
the sum of the protons and neutrons
– Isotopes
• atoms with the same number of protons (and
therefore the same element) but with a
different number of neutrons.