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423 BCE
plato
solid forms of matter are composed of indivisible elements shaped like triangles. -
400 BCE
Democritus
atoms are uniform, solid, hard, incompressible, and indestructible and that they moved in infinite numbers through empty space until stopped. -
330 BCE
Aristotle
the four elements are not composed of atoms but were continuous forms of matter. -
Robert boyle
everything is composed of very tiny particles, an idea known as atomism. -
John dalton
the atom with the number of protons and neutrons in the nucleus, as well as the number of electrons in each of the electron shells. -
Newlands Law of Octaves
elements are arranged in increasing order of their atomic masses, the properties of the eighth element are a repetition of the properties of the first element. -
Mendeleev periodic table
a periodic table of all the elements that were known at the time. -
Photoelectric effect
the energy from photons is absorbed by matter, the matter can emit electrons. -
discovery of radiation
radiation was accidentally discovered when Henri Becquerel saw that uranium salts spontaneously emit a penetrating radiation that can be registered on a photographic plate -
Planck quantum theory of light
the energy of light is proportional to frequency, and Planck's constant is the constant that relates them. -
Plum pudding model
the electrons are negatively charged particles embedded in a ton of positive charge. -
Robert Millikan
Small electrically charged drops of oil were suspended between two metal plates where they were subjected to the downward force of gravity and the upward attraction of an electrical field. -
Rutherford gold foil experiment
this all showed that the atom is mostly empty space with a tiny, dense, positively-charged nucleus. -
Bohr's Planetary Model
The Bohr model postulates that electrons orbit the nucleus at fixed energy levels. Orbits further from the nucleus exist at higher energy levels. When electrons return to a lower energy level, they emit energy in the form of light -
Moseley atomic number
the atomic number is the number of positive charges in the atomic nucleus. -
discovery of the proton
Hydrogen nuclei were observed by shooting alpha particles at a tube full of hydrogen and occasionally the alpha particle would knock a hydrogen nucleus out of the atom. Those nuclei hit detectors that gave off sparkling light when they were hit -
schrodinger equation
The transformation of the physical quantity overtime, where the quantum effects are like a wave-particle duality. -
Heisenberg uncertainty principle
you can either know how fast it is going, or where it's located, but not both at the same time without being uncertain. -
Discovery of the neutron
James Chadwick announced that the core also contained a new uncharged particle, which he called the neutron. -
the alchemists
All metals were formed of sulfur and mercury in various proportions and that altering those proportions could transform the metal under study.