Atomic Structure- History
and The Nucleus
Philosophers and Scientists
• Know how the following contributed to the history
of the atom:
Philosophers from History of the Atom video
– Empedicles
– Leucippus
– Aristotle
– Gassendi
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
Next week
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
– the center of the atom composed of protons
and neutrons
– 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 (+ charged) in the nucleus
• The # of electrons (- charged) equals the # protons
in a neutral atom.
– 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.