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Period: 460 BCE to 370 BCE
Democritus
Came up with the Atomic Theory - everything is composed of atoms.
Atoms are the basic building block of matter.
Atoms cannot be cut.
Atoms are the smallest units of matter that still retain the identity and the properties of that matter. -
Period: 384 BCE to 322 BCE
Aristotle
He opposed Democritus.
Aristotle believed in the four elements: Earth, Air, Fire and Water.
He didn’t believe in the atomic theory. -
Period: 300 BCE to 300 BCE
Alchemy
The art of understanding, deconstructing and reconstruction of matter.
He believed Aristotle, and that everything is made up of Earth, Air, Fire and Water.
Believed that he could turn all metals into gold by the Philosopher’s stone.
Alchemists were split. one group focused on discovering new compounds, reactions and chemical processes.
They discovered distillation, percolation, extraction, rudimentary, and chromatography -
Period: to
Robert Boyle
Studied gases and the inverse relationship between volume and pressure of gas. -
Period: to
Carl Wihelm Scheele
He discovered the absorption of gases by charcoal.
Carl also discovered chemical counpounds and elements such as: Manganese, Barium, Lactic Acid, Glycerin, Molybdenum, and Chlorine.
He is known for the discovery of, “oxygen”, in the air. -
Period: to
Anton Laurent de La Voisier
“Father of Modern Chemistry”.
He discovered the Law of Conservation of Mass, that the mass of a metal oxide is equal to the mass of the metal plus oxygen when the metal oxide decomposes.
Anton believed that matter can change form, but can’t be destroyed or created in a chemical form. -
Period: to
Benjamin Franklin
Discovered that electrical charges come in 2 varieties - positive and negative. Like charges can repel, oppositie charges attract. -
Period: to
Joseph Louis Prorust
He developed a Law of Definite Proportions, sometimes called the Law of Constant Compostion - a chemical compound always contains the same proportion of elements by mass. -
Period: to
John Dalton
Matter is made up of atoms that are invisible and indestructible.
All atoms of an element are identical.
Atoms of different elements have different weights and different chemical properties.
Atoms of different elements combine in simple whole numbers to form compounds.
Atoms cannot be created or destroyed.
When a compound decomposes, the atoms are recovered unchanged. -
Period: to
Amedeo Avogadro
Worked off of Boyle’s teachings.
Found the difference between atoms and molecules. -
Period: to
William Crookes
Discovered the element thallium, and his studies on cathode rays are now fundamental in physics. -
Period: to
Dmitri Mendeleev
Developed the first Periodic Table of Elements.
Table was upgraded from 63, to 92 elements. -
Period: to
Sir John Joseph Thomson
Developed the electron by experimenting with Crookes.
He showed that electrons are negatively charged. -
Period: to
Millikan
Calculated the mass and charge of an electron.
Discovered radioactivity in uranium one.
Discovered and isolated polonium and radium from uranium one. -
Period: to
Ernest Rutherford
Classification of radiation.
Discovered alpha and beta rays.
Identified alpha particles as helium nuclei. -
Period: to
Niel’s Bohr
Photons are emitted from an electrically atom only at certain frequencies.
He believed that electrons inhabit energy levels, and that there is only light when the electron is forced to change energy levels. -
Period: to
Dorothy Mary Hodgkin
She was a British chemist and a scientist.
She studied X-ray crystallography.
Dorothy confirmed the structure of penicillin along with insulin.