Download Notes ch 3.2 - Douglas County

Notes ch 3.2
Discovery of subatomic particles
Modern atomic theory
Discovery of electrons
JJ Thomson
Nucleus Ideas
• JJ Thompson :(
(Plum Pudding Model, 1904)
=ball of positive charge with electrons throughout
• Ernest Rutherford
(Nuclear Model, 1909)
=dense, positive charged mass, concentrated in a
small nuclear area
Discovery of the nucleus
Today
• Daltons basic ideas survive.
• We now know there are versions of
elements (isotopes)
• We now know that atoms can be
subdivided. (They have parts p, n, e)
• Atoms became visible to researchers in the
1980’s with the use of a scanning tunneling
microscope.
What did each of the following contribute to
development of atomic theory?
JJ Thompson:
Ernest Rutherford:
Democritus:
Nuclear atom or plum pudding?
•
•
JJ Thompson’s
•
model
Ernest
Rutherford’s
“Plum Pudding”
Nuclear Atom
Nuclear particles
• Proton
• Neutron
– Positive charge
• Mass 1.67 x10-24g
•
• Is the defining particle of •
an atom.
•
Gives the atom its identity.
– No electric charge
Mass = to a proton
Adds to the mass of the atom
Gives nucleus stability
(separation of + charges)
Unit of mass used is the AMU
Atomic Mass Unit= ~ the mass of a proton.
Really, 1/12 of a carbon-12 atom
Proton = element defining particle
• # of protons = atomic #
Ex: Oxygen = 8 protons, has atomic number of 8
Neon = 10 protons, has atomic number of 10
• How many protons does carbon have?
• Calcium?
Sub atomic particles
Particle
Charge
Symbol
Electron
-1
e-
mass
(amu)
1/2000
Proton
+1
p+
1
0
n
1
Neutron
Essentially all of the mass of an atom comes from the nuclear
particles (protons and neutrons)
Summary
• Mass number (A) = nucleus number
– Protons + Neutrons
• Atomic number (Z) = # of protons
• Number of Neutrons = mass number – atomic
number (A-Z)
• An element is neutral (no net charge) if the # of
electrons= # of protons