-
500
Democritus ( Structure of an atom)
He formulated his own Democritus Atomic Model. His atomic theory states that everything is physically made op of atoms. He stated that atoms are indivisible and can never be broken down into pieces. He added that in between atoms are empty spaces, the more empty space the heavier the atom gets. This on the other hand was opposed and is only based on his opinions but not studied geometrically. Democritus Atomic Model talks about the atoms that can never be destroyed nor created. -
500
Aristotle (4 Elements)
He made a great generalizaton off all matter being made of the four elements: Fire, water, earth, and air.
Earth, which is cold and dry; this corresponds to the modern idea of a Solid.
Water, which is cold and wet; this corresponds to the modern idea of a Liquid.
Air, which is hot and wet; this corresponds to the modern idea of a Gas.
Fire, which is hot and dry; this corresponds to the modern idea of a Heat. -
John Dalton (Father of atomic thoery)
John Dalton was a school teacher who developed the modern atomic theory by experimentation that all matter is made of atoms, atoms of a particular element are all the same size, mass and chemical property. He also proposed that all atoms can not be created, divided, or split. -
Marie Curie ( Radium and Polonium)
A polish scientist who won two nobel prizes (one in physics and one in chemistry) and that is a record tht still stands today. She was the first to use the word "radiation" to describe the strange energy source that came from radioactive isotopes. She also discovered two new elements, radium and polonium. She was also the first to use radioactive materials to help treat cancers. -
Ernest Rutherford (Gold foil experiment)
New Zealander who leaded the "gold foil experiment" disproved the plum pudding model of the atom but proved that the atom must have a small positively charged nucleus and the rest of the atom was mostly empty space. -
Period: to
Niels Bohr
-
Period: to
Niels Bohr
-
Henri Becquerel ( Radioctivity)
Henri Becquerel discovered radioactivity. It happened by accident when he was investigating phosphorescence. Becquerel was aware of Roentgen’s discovery of x-rays in 1895 and thought there might be a relationship between phosphorescence and x-radiation. -
J.J.Thomson (cathode rays)
he discover the electron, (electron with the negative charge). Hediscovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube, an area being investigated by numerous scientists at the time. Thomson interpreted the deflection of the rays by electrically charged plates and magnets as evidence of "bodies much smaller than atoms" that he calculated as having a very large value for the charge-to-mass ratio. Later he estimated -
Robert Millikan ( oil-drop experiment
An "atomizer" from a perfume bottle sprayed
oil or water droplets into the sample chamber.
Some of the droplets fell through the pinhole
into an area between two plates (one positive
and one negative). This middle chamber was
ionized by x-rays. Particles that did not
capture any electrons fell to the bottom plate
due to gravity. Particles that did capture one
or more electrons were attracted to the
positive upper plate and either floated upward
or fell more slowly. -
Niels Bohr (Planetary Model)
Bohr suggested that the outer orbits could hold more electrons than the inner ones, and that these outer orbits determine the atom's chemical properties. Bohr also described the way atoms emit radiation by suggesting that when an electron jumps from an outer orbit to an inner one, that it emits light. Later other physicists expanded his theory into quantum mechanics. This theory explains the structure and actions of complex atoms. -
Quantum Model
The Quantum model also includes a nucleus containing neutral particles known as a neutrons and positive particles called protons. This protron-electron model accounts for the whole number rule for isotopes masses and is consistent with the emission of alpha (He) and beta (electron) particles. -
James Chadwick ( Neutron)
Chadwick made a fundamental discovery in the domain of nuclear science: he proved the existence of neutrons - elementary particles devoid of any electrical charge. In contrast with the helium nuclei (alpha rays) which are charged, and therefore repelled by the considerable electrical forces present in the nuclei of heavy atoms, this new tool in atomic disintegration need not overcome any electric barrier and is capable of penetrating and splitting the nuclei of even the heaviest elements
