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300
Aristotle
(300BC) a Greek philosopher taught that only four elements were used in various complications to make everything in the universe. The elements were earth, fire, air, and water. -
300
Alchemists
tired to discover how to change lead into gold. He was convinced that matter was only made of a few substances and by rearranging the substances they could be turned into another. So he tried to turn a worthless material into a valuable material like gold. He also tried to find the secret to eternal life. Though the ideas seem strange it had an important effect on science because the work helped lead us to what is now known as chemistry. -
430
Democritus
(430BC0 He taught that matter was made of small particles he called atoms. His ideas were rather close to what now is thought to be true about matter, but for 2,000 years after his death people continued to believe the four elements that Aristotle composed. -
John Dalton
He hypothesized that the elements must be made up of smaller, invisible, pieces of matter. He called these pieces of matter atoms. He discovered atomic weights -
Dmitri Mendeleev
Organized the 60 elements into a table and called it the periodic table. -
JJ Thomson
In the late 19th century he was a scientist who stated that atoms were not simple solid spheres. He discovered electrons. -
Ernest Rutherford
He developed a more complete understanding of structure of atoms. He concluded that atoms are mostly made of space. He also called the positively charged center of the atom the nucleus. He stated that all of an atoms positively charged particles were in the nucleus and negatively charged particles were around the perimeter of the atom. -
Henry Moseley
He suggested that it is the atomic number, rather then the atomic weight that identifies the properties. -
Neilis Bohr
He proposed that electrons orbit around the nucleus. He stated that each electron has a fixed amount of energy, and that the electrons orbit within energy levels, forming rings around the nucleus. -
Erwin Schrödinger
He took the Bohr atom model one step further. Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position.
