-
340
Aristotle
340 B.C
Aristotle didnt think atoms could be constantly moving. He believed there were four elements only, water, fire, air and earth and that they would align into their rightful place and be at rest. -
400
Democritus
400 B.C
The Idea of the atom were first proposed by the Greek philosophers Democritus and Leucippus around 400 B.C. At the time there was no real evidence to support the proposal. The atom was suggested to be what all matter is made of. -
Robert Boyle
He measured relationships between volume and pressure of gases. From his experiments he concluded that gases are made up of tiny particles that group together to make different substances. -
Antoine Lavoisier
Antoine created the idea of having a single language for all of science to use. For example when someone called a substance hydrogen, than everyone was to call it hydrogen. This allowed for science to advance and for chemists to learn new properties of other metals and know how to organize them without getting confused of different names from different languages -
John Dalton
He claimed the reason elements combined was because all elements are made up of atoms. He also published a three- part atomic theory. 1. All particles are made of atoms, they cant be divided or destroyed. 2.Atoms of the same elements are identical and different element's atoms are different. 3. Atoms join with other substances to create new and different substances. -
Johann Dobereiner
Johann Dobereiner noticed that the atomic weight of strontium fell midway between the weights of calcium and barium which were elements possessing similar properties, In 1829, after discovering the halogen triad composed of chlorine, bromine, and iodine and the alkali metal triad of lithium, sodium and potassium he proposed that the middle element had to be an average of the other two elements this was called the Law of Triads -
Alexandre-Emile Béguyer de Chancourtois
French geologist who arranged the elements in order of increasing atomic weights. He plotted the elements on a cylinder, which he called the telluric helix. Alexandre-Emile Béguyer de Chancourtois listed the elements on paper tape and wound them, spiral like, around a cylinder. Certain ‘threes’ of elements with similar properties came together down the cylinder. -
John Newlands
John having arranged the 62 known elements in order of increasing atomic weights, noted that after interval of eight elements similar physical/chemical properties reappeared. Newlands was the first to formulate the concept of periodicity in the properties of the chemical elements. In 1863 he wrote a paper proposing the Law of Octaves -
Dimitri Mendeleev
In 1869, Russian chemist Dimitri Mendeleev produced a periodic table based on atomic weights. He found that the table showed similarities in vertical, horizontal, and diagonal. Elements with similar properties appeared under each other. He left room for elements that he knew where to be found. -
J.J Thomson
Thomson used a cathode ray tube to infer that there are small particles inside of every atom. This inference proved Dalton's theory to be wrong. Particles can be divided. Through this experiment Thomson also inferred that atoms must be negatively charged.Thomson purposed the plum pudding model which allowed scientefic advances to occur. -
Hantaro Nagaoka
In 1904, Hantaro Nagaoka developed an early but incorrect planetary model of the atom. He based his model of the atom around the rings of the planet saturn. However his model was not created properly. He explained that the rings are held there due to its massive orbit. Although this model was wrong it still allowed for the discovery of the atoms shells. -
Ernest Rutherford
In his expirament Rutherford shot a positively charged beam of particles through a sheet of gold foil. He thought if the particles were soft as J.J Thomson's plum pudding model had suggested than they would pass through and continue in a straight line, Which most did. However some did not this showed that the plum pudding model was somewhat false, so Rutherford created a new model. -
Moseley
Moseley arranged the elements according to increasing atomic numbers and not atomic masses, some of the inconsistencies associated with Mendeleev's table were eliminated. The modern periodic table is based on Moseley's Periodic Law -
Neils Bohr
Neil suggested that electrons travel around the nucleus in definite paths. These paths are always at a certain "level" away from the nucleus. He also stated that electrons cannot travel in between each path, however they can jump from one path to another.
