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350
Aristotle
350 BC; A Greek philosopher, Aristotle disagreed with Democritus's atom model. Majority of his ideas were more thought based than scientifcially based. Thus Aristotle strongly disagreed with Democritus. He assumed that different substances were made of air, earth, fire, and water. He didn't have an atomic model due to the fact that he thought atoms were non existent. -
400
Democritus
400 BC; Democritus was the first scientist to create a model of the atom, which was just a round solid ball. He discovered that all matter is made up of invisible, solid, insdestructable, and unique particles called atoms and created the name "atom" from the Greek word "atomos", translating to uncuttable. -
Robert Boyle
Robert Boyle studied the pressure of gases and concluded that gases had tiny particles that combine together to form substances. -
Antoine Lavoisier
French nobleman, Lavoisier founded several elements, and formed together the first table of elements. He used Aristotle's idea of air, earth, fire, and water to execute experiments to invesigate combustion and oxidation. By using previous knowledge of atomic bonding, he discovered other elements like hydrogen, oxygen, and sulfur, and discovered that water was made of oxygen and hydrogen, and air included nitrogen. -
John Dalton
English chemist, John Dalton created the Atomic Theory of Matter, a composition of his own and previous findings by Democritus. In this theory, he included that all matter is made of atoms that cannot be created nor destroyed, and atoms of different elements combine in whole ratios to form chemical compunds. -
Alexandre Béguyer de Chancourtois
Geologist, Alexandre created the 'vis tellurique' (telluric screw), a 3D arrangement of the elements. The telluric screw arranged the atomic weights on the outside of a cylinder, thus one complete turn corresponded to an atomic weight increaseof 16. This arrangement means that certain elements with similar properties appear in a vertical line. -
John Newlands
4 years before Mendeleev published his periodic table, Newlands noticed that there were similarities between the atomic weights that differed by 7, and he called this The Law of Octaves. Newlands didn't leave any room for undiscovered elements in his table, and even had to cram two elements into one box to keep the pattern. Therefore, the Chemical Society refused to publish his paper. -
Julius Lothar Meyer
His first table consisted of 28 elements, arranged by their valency (amount of other atoms they can combine with). But in his second table, he incorporated the transition metals. This table listed the elements in the order of atomic weights, with elements of the same valency organised in vertical lines, extremely similar to Mendeleev’s table. -
Dmitri Mendeleev
Mendeleev discovered the periodic table and arranged the elements by writing the elements' properties on pieces of card then arranging and rearranging them until he noticed that, by ordering the increase atomic weight, certain types of elements occurred regularly. Initially, the table had similar elements in horizontal rows, but he then organised them to fit in vertical columns. -
Julius Lothar Meyer
Meyer's more developed table was published 2 years after he created his second table, and a year after the publishing of Mendeleev’s periodic table. Even after 1870, Meyer and Mendeleev were unaware of each other’s work, despite Meyer later admitting that Mendeleev had published his version first. -
J.J. Thomson
Thomson discovered the electron, which led him to create the Plum Pudding Model. In this model, he assumed that the atom was mainly positive, and negative electrons wandered around the atom. -
Marie and Pierre Curie
After radiation was discovered by Henri Baquerel, Marie decided to look further into this discovery. Through this she and her husband discovered the elements Radium and Polonium and won the Nobel Peace Prize for their works in radioactivity. -
Hantaro Nagaoka
Nagaoka created an incorrect atom model that was comparable to Saturn and its rings, which lead to the discovery of atom rings. -
Robert Millikan
American scientist, Millikan was very interested in J.J. Thomson's finding of the electron. J.J. Thomson predicted that the electron was 1000 time smaller than the atom and Millikan wanted to prove this hypothesis. He preformed an "oil-drop experiment" in which he found that J.J. Thomson was correct. -
Ernest Rutherford
Rutherford felt that J.J. Thomson's model was incorrect, so he created a new one. He created the nucleus, and said that instead of the whole atom being made of positive matter, it was in the centre. He said the atom was mostly empty space and that the electrons surrounded the positive nucleus. -
Moseley
English scientist, Moseley worked with Niels Bohr to create the accurate atomic number. Moseley used X-rays to find the element frquencies on the periodic table. He used these frequencies to find that the number of protons in the nucleus correlated with the atomic number. This created Moseley's Law. -
Niels Bohr
Danish scientist, Bohr decided to make a new model based off of Rutherford's but changed the orbit of the electron. He also created energy levels in the atom, where only a certain amount of electrons could fit on one energy level. -
Jame Chadwick
English scientist, Chadwick first discovered the neutron. Before this discovery, Rutherford had concluded that the nucleus was made of positive matter, and that the atom was neutral since the negative electrons and the positive protons cancelled out. But, Chadwick started to question why there's a difference between the atomic mass and the number of protons. Chadwick then found that the missing component was a neutral part: the neutron.
