Download Tuesday, October 15 B-Day

Tuesday, October 15
B-Day
New Unit, Pick up a cover sheet.
Transfer Unit 2 to your binder.
History of the Atom
• Early Greek PhilosophersDemocritus
– 460- 370 B.C.
– All things are “composed of
minute, indestructible
particles.
– These particles are pure
matter and are mostly empty.
John Dalton- Atomic Theory 1803
• Atoms of different elements
combine in whole number
ratios.
• Atoms could not be divided or
destroyed.
• Different elements contain
different chemical properties.
• Atoms of the same element
contain the same chemical
properties.
JJ Thompson 1897
• Created Tube with + charged anode on one
side and a – charged cathode on the other.
Two strong magnets were placed in the
middle of the tube.
• Shot a cathode ray (stream of electrons)
through the tube.
• Results- The ray was deflected toward the
positive magnet.
• Conclusion- The beam was composed of
negatively charged particles.
Ernest Rutheford
• Experiment
– Shot alpha particles (+ protons) through a thin
layer of gold foil.
– Fluorescent screen used to detect path of
particles.
• Result 1: Most of the alpha particles went
straight through the gold foil.
• Conclusion 1: Atom is mostly empty space.
• Result 2- A few of the particles were deflected
back or hit the screen at angles.
• Conclusion 2- The Center of the atom is dense,
positive, and very small.
Rutherford’s Model
Think/Pair/Share
In what ways did
Thompson’s work
help Rutherford to
develop his model?
Niels Bohr (1913) Planetary Model
• Electrons revolve in orbits of specific radius
around the nucleus without emitting radiation;
• Within each orbit, each electron has a fixed
amount of energy; electrons in orbits farther
away from the nucleus have greater energies;
• An electron may ‘jump’ from one orbit of high
energy to another of lower energy causing the
energy difference to be emitted as a photon of
electromagnetic radiation such as light;
Bohr Model
Modern Models
• Developed through quantum physics and
mathematical models.
• Instead of orbits electrons move in orbitals
• Instead of a pre-determined path, electrons
move around in an area.
Summary of what we know…
Subatomic
Particle
Proton
Symbol
1
p
Relative
Charge
Relative
Mass (amu)
+1
1 amu
0
1 amu
-1
0 amu
+1
Neutron
1n
0
Electron
0e
-1
AMU
• Atomic mass unit- the standard unit that is
used for indicating mass on an atomic scale.
• One amu= mass of one proton or neutron.