-
Lab procedures were developed, but alchemists did not
perform controlled experiments like true scientists. -
Proposed that matter was composed of tiny indivisible particles
-
Elements are made of
tiny particles called
atoms. -
Conservation of atoms—
rearrangement in RXN
(Lavoisier previously stated
this in terms of the Law of
Conservation of Matter) -
Different atoms form
compounds in constant
ratios. -
British Schoolteacher
– based his theory on others’
experimental data -
Billiard Ball Model
– atom is a
uniform,
solid sphere -
The structure of
atoms is
somehow related
to electricity -
Three types:
– alpha () - positive
– beta () - negative
– gamma () - neutral -
Discovered radioactivity
– spontaneous emission of
radiation from the nucleus -
Discovered atoms have
negative particles
(electrons) using a
cathode ray tube. -
Discovered electron’s
charge to mass ratio:
1.76 x 108
C/g -
came up with the term “isotope” to explain the unintentional breakdown of radioactive elements.
-
Cathode Ray Tube
Experiments
– beam of negative particles -
Plum-pudding Model
-
Discovered Electrons
– negative particles within
the atom -
Plum-pudding Model
– positive sphere
(pudding) with
negative electrons
(plums) dispersed
throughout -
Atoms of one element are
identical while atoms of
different elements are
different -
proposed an atomic model called the Saturnian Model to describe the structure of an atom.
-
found that inert gases have a “stable electron configuration.
-
invented a device that could detect alpha particles.
-
Measured the
charge of an
electron using oil
droplets -
Electron’s charge:
1.60 x 10-19 C -
Electron’s mass:
9.11 x 10-28 g -
Gold Foil Experiment
-
Discovered the nucleus
– dense, positive charge in
the center of the atom -
Nuclear Model
– dense, positive nucleus surrounded
by negative electrons -
Bright-Line Spectrum
– tried to explain presence
of specific colors in
hydrogen’s spectrum -
Energy Levels
– electrons can only exist in
specific energy states -
Planetary Model
– electrons move in circular
orbits within specific
energy levels -
discovered that the number of protons in an element determines its atomic number
-
used a mass spectrograph to identify 212 isotopes.
-
An electron does not travel in an exact orbit
-
We can predict where it will probably be
-
We cannot say for certain where it is, but only where it ought to be
-
The type of probability orbit is dependent on the energy level described by Bohr
-
proposed an atomic structure theory that stated the outer orbit of an atom could hold more electrons than the inner orbit.
-
roposed that electrons have a wave/particle duality.
-
Quantum mechanics
– electrons can only exist in
specified energy states -
Electron cloud model
– orbital: region around the
nucleus where e- are likely
to be found -
Electron Cloud Model (orbital)
• dots represent probability of finding an enot actual electrons -
created the first nuclear reaction, producing alpha particles
-
proposed the existence of anti-particles
-
discovered neutrons, particles whose mass was close to that of a proton.
-
Discovered neutrons
– neutral particles in the
nucleus of an atom -
Joliot-Curie
Experiments
– based his theory on their
experimental evidence -
Neutron Model
• revision of Rutherford’s Nuclear Model -
discovered nuclear fission.
-
discovered eight transuranium elements.
-
created the first man-made nuclear reactor.