-
428 BCE
Plato
the Plato theory is that the physical world is not real. It is the way of understanding reality. -
400 BCE
Democritus
Democritus discovered that all material bodies are made up of super small atoms. He originally had named atoms "atomos." -
330 BCE
Aristotle
Aristotle thought that there must be a separate and unchanging being that is the source of all other beings. He believed that the four elements, hot, cold, wet, and dry could be combined to form elements like water, fire, earth and air that all the other philosophers believed in. -
500
The Alchemists
They believed that the world and everything in it were composed of the 4 elements, water, fire, earth, air also essential substances like, mercury, salt, and sulfur. -
Lavoisier
In June 1783, Lavoisier reacted oxygen with inflammable air, obtaining "water in a very pure state." His conclusion was correct, water was not an element but a compound of oxygen and inflammable air, or hydrogen as it is now known -
John Dalton
John Dalton was an English chemist, physicist and meteorologist. He introduced atomic theory into chemistry. First part, all matter is made of atoms, which are indivisible. Second part, all atoms of a given element are identical in mass and properties. Third part, compounds are combinations of two or more different types of atoms. -
New Lands of Octaves
JAR Newland made this law in 1865. The law was If the chemical elements are arranged according to increasing atomic weight, those with similar physical and chemical properties occur after each interval of seven elements. -
Mendeleev's Pd. Table
Mendeleev placed elements in the order of their atomic weights in the form of a table known as the Periodic table of Mendeleev. Mendeleev arranged elements in rows by increasing atomic mass. -
Photoelectric Effect
Photoelectric Effect is electrically charged particles are released from or in a material when it absorbs electromagnetic radiation. -
Discovery of Radioactivity
On March 1st, 1896, Henri Becquerel discovered radioactivity. His discovery was accidental after he opened a drawer and discover spontaneous radioactivity. -
Discovery of the electron
An English physicist J.J. Thomson discovered the first electrons. He discovered them by experimenting with a Crookes, or cathode ray, tube. -
Charge of the Electron
Robert Millikan charged droplets of oil between two electrodes and balanced the gravitational force with the upward forces, using mechanical equilibrium to determine the charge -
Plum Pudding Model
The Plum Pudding Model is a scientific model of an atom. It is when electrons surrounded by a volume of positive charge. It was discovered by J.J Thomson in the 19th century -
Planck's Quantum Theory of Light
Planck's Quantum theory is when different atoms and molecules can emit or absorb energy in discrete quantities only. -
Robert Millikan
Robert Millikan was a physicist who discovered the elementary charge of an electron using the oil-drop experiment. -
Rutherford's Gold Foil Experiment
The Rutherford Gold Foil Experiment is when a beam of alpha particles are aimed at a piece of gold foil. Most alpha particles passed through the foil, but a few were scattered backward. This showed that most of the atom is empty space surrounding a tiny nucleus. -
Bohr's Planetary Model
The Bohr's Planetary Model is when the electrons encircle the nucleus of the atom in specific allowable paths. The paths were called orbits. -
Mosley's Atomic Numbers
In 1914, Mosley observed and measured the X-ray spectra of various chemical elements using diffraction in crystals. Through this, he discovered a systematic relation between wave- length and atomic number. -
Discovery of the proton
In the early 1900's the proton was discovered by Ernest Rutherford. His research resulted in a nuclear reaction where he then discovered the protons. -
Schrodinger Equation
The equation is a linear partial differential equation. It governs the wave function of a quantum-mechanical system. The equation was developed by Erwin Schrodinger. -
Heisenberg Uncertainty Principle
In 1927, a German physicist and Nobel laureate named Werner Heisenberg formulated this principle. The Heisenberg Uncertainty principle is when we cannot know both the position and speed of a particle, such as a photon or electron, with perfect accuracy. -
Discovery of the Neutron
In May 1932 James Chadwick announced that the core also contained a new uncharged particle. He discovered it by firing alpha radiation at a beryllium sheet from a polonium source. He then called it a neutron.
