-
Jan 1, 1000
Aristotle BCE 382
Aristotle, a Greek philosopher, Disagreed with Dimocritus's theory. He believed that you could never end up with a particle that could not be cut. Aristotle had influenced so many people that they believed in his theory even though he was wrong. -
Jan 1, 1000
Democritus 440 BCE
Democritus was a Greek philosopher who figured that if one cut substance in half over and over one would end up with a particle that could not be cut. He named this particle an atom. -
John Dalton
John Dalton was a British chemist and teacher, who tested different substances to find out why elements combine in certain proportions based on mass to form compounds. He came up with an atomic theory with three main ideas. Fist, all substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed. Second, atoms of the same element are exactly alike, and atoms of different elements are different. Atoms join with other atoms to make new substances. -
J.J. Thomson
J.J thomson, a British scientist, discovered that atoms have small particles inside of them and can be split into smaller parts. He made his discovery useing a cathode-ray tube. With this instroment he saw that the smaller particles inside of an atom are negativly charged. These smaller particles are called electrons. -
Ernest Rutherford 1909
Rutherford tested Thomson's theory by aiming positivly charged particles at a sheet of gold foil. When the particles hit the gold some went straight through, a few bounced back, and others went to the side. This means that thomson's theory was wrong. He then realized that atoms must be considered mostly empmty space, with a tiny part made of highly dense matter. -
Ernest Rutherford
Rutherford changed the original atomic theory by makeing a new model of the atom. In the new model the center of the atom is a tiny, very dense, positivly charged part called the nucleus. He knew that like charges repel so the particles around the nucleus were also positvly charged. Rutherfors calculated that the nucleus was 100,000 times smaller than the diammeter of the gold atom. -
Niels Bohr
Bohr studied the way atoms ereact to light. His studies led him to believe that electrons move in certain energy levels or paths around the nucleus. The electons can hop from a certain energy level to another. -
Schrodinger and Heisenberg
Erwin Schrodinger and Werner Heisenberg created todays atomic theory. They discovered that electrons do not move in certain paths. The path of an atom is unpredictable. They also discoveredd electron clouds regions where electrons are very likely to be found. -
Period: to
The Development of the Atomic Theory
