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Glow in the Dark
Chemistry Sheds Light on Our Lives
Unit 4 Atoms and Light
Glow in the Dark
4.1 Development of Atomic Theory
4.2 Atomic Structure
4.3 Electron Structure
4.4 Periodic Table
4.5 Periodicity
4.6 Light
4.7 Light and Matter
4.1 & 4.2 Atomic Theory and
Atomic Structure
Objectives
• Determine the location, charge, and relative mass
of protons, neutrons, electrons.
• Use symbols in writing isotope notation.
• Identify isotopes using mass number and atomic
number and determine the number of protons,
neutrons and electrons.
• Differentiate actual atomic mass of an element from
the mass number of an isotope
• Calculate average atomic mass from %
abundances of an isotope
Atomic Structure Timeline
On Wednesday’s quiz, you will be expected
to…
match scientists to their experiments and
discoveries
place the models in chronological order
Democritus (400 B.C.)
• Proposed that matter was
composed of tiny indivisible
particles
• Not based on experimental
data
• Greek: atomos
Alchemy (next 2000 years)
• Mixture of science and mysticism.
• Lab procedures were developed, but alchemists did not perform controlled
experiments like true scientists.
John Dalton (1807)
British Schoolteacher
based his theory on others’
experimental data
Billiard Ball Model
atom is a
uniform,
solid sphere
John Dalton
Dalton’s Atomic Theory
1. All matter is made of tiny particles “atoms”
2. Atoms cannot be created, divided, destroyed
or changed into other types of atoms
3. Atoms of the same element have identical
properties
4. Atoms of different elements have different
properties
5. Atoms of different elements combine in
whole-number ratios to form compounds
6. Chemical changes join, separate or
rearrange atoms in compounds
Henri Becquerel (1896)
Discovered radioactivity
spontaneous emission of
radiation from the nucleus
Three types:
alpha () - positive
beta () - negative
gamma () - neutral
J. J. Thomson (1903)
Cathode Ray Tube
Experiments
beam of negative particles
Discovered Electrons
negative particles within the
atom
Plum-pudding Model
Cathode Ray Tubes
A cathode ray is a ray of light traveling in a vacuum (no other particles inside)
The ray travels from one metal plate to another as the plates are connected to electricity
Cathode ray
Metal plate
(cathode) releases
stream
Metal plate (anode) to
which stream travels
Cathode Ray Tubes & Charge
In the late 1800’s, JJ Thomson put charged plates outside the tube
Negatively charged plate
-
+
Positively charged plate
Ray is deflected
away from negative
plate and towards
positive plate
It made no difference what type of metal he used in the tube—all material produced this
stream that curved towards the positive charge
J. J. Thomson (1903)
Plum-pudding Model
positive sphere (pudding) with
negative electrons (plums)
dispersed throughout
Chocolate Cookie Model
Dough is positive area and
chips are negative electrons
Robert Millikan (1909)
• Balanced the downward
gravitational force and the
upward electrical and
buoyant forces of charged
oil droplets suspended
between two metal plates.
• Discovered the
charge of an
electron
Ernest Rutherford (1911)
Gold Foil Experiment
Discovered the nucleus
dense, positive charge in the
center of the atom
Nuclear Model
Ernest Rutherford (1911)
Ernest Rutherford (1911)
Nuclear Model
dense, positive nucleus
Mainly empty space filled with electrons
Niels Bohr (1913)
Bright-Line Spectrum
tried to explain presence of
specific colors in hydrogen’s
spectrum
Energy Levels
He stated that electrons can only
exist in specific energy states
Planetary Model
Niels Bohr (1913)
Bright-line spectrum
Planetary Model
electrons move in circular orbits
within specific energy levels
Erwin Schrödinger (1926)
Quantum mechanics
electrons can only exist in
specified energy areas
Electron cloud model
orbital: region around the
nucleus where e- are likely to
be found
James Chadwick (1932)
Discovered neutrons
neutral particles in the nucleus of
an atom
Joliot-Curie Experiments
based his theory on their
experimental evidence
James Chadwick (1932)
Neutron Model
revision of Rutherford’s Nuclear Model
Make a chart like the one below and
fill it in to help you study for your quiz.
Scientist
Experiment
Discoveries
Dalton (1809)
Other’s data
6 postulates
Billiard Ball
(two were later
Model
proven incorrect)
Thomson (1903)
Millikan (1909)
Rutherford (1911)
Bohr (1913)
Bright-Line
Spectrum
Schrödinger (1926)
N/A
Chadwick (1932)
N/A
New model
described
New model
drawing