Chemistry Timeline

Year | Scientists | Discovery | Atomic Model |
429BC – 432BC | Empedocles | Empedocles argued that all matter was composed of four elements: fire, air, water, and earth. | |
460BC – 370BC | Democritus | "by convention bitter, by convention sweet, but in reality atoms and void" | |
384BC – 322BC | Aristotele | Accepted the theory of Empedocles, adding his own (incorrect) idea that the fourcore elements could be transformed into one another. | |
1643 | Evangelista Torricelli | Showed that air had weight and was capable of pushing down on a column of liquid mercury (thus inventing the barometer). This was a startling finding. If air - this substance that we could not see, feel, or smell - had weight, it must be made of something physical. | |
1643 | Daniel Bernoulli | Hedeveloped a theory that air and other gases consist of tiny particles that are too small to be seen, and are loosely packed in an empty volume of space. The particles could not be felt because unlike a solid stone wall that does not move, the tiny particles move aside when a human hand or body moves through them. Bernoulli reasoned that if these particles were not in constant motion they would settleto the ground like dust particles. | |
1660 | Robert Boyle | Boyle proposed a new definition of an element as a fundamental substance, and we now define elements as fundamental substances that cannot be broken down further by chemical means. | |
1704 | Isaac Newton | Proposed a mechanical universe with small solid masses in motion. | |
1773 | Joseph Priestley | Priestley had observed thatit does not just turn into mercury; it actually breaks down into two substances when it is heated, liquid mercury and a strange gas. Priestley’s discovery revealed that substances could combine together or break apart to form new substances with different properties. | |
1778 | Antonie Lavoisier | Lavoisier established the Law of Conservation of Mass, which says that mass is not lost or gainedduring a chemical reaction. | |
1779 - 1804 | Joseph Proust | Proust performed a number of experiments and observed that no matter how he caused different elements to react with oxygen, they always reacted in defined proportions. (Law of Definite Proportions) | |
1803 | John Dalton | Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass. | |
1832| Michael Faraday | Studied the effect of electricity on solutions, coined term "electrolysis" as a splitting of molecules with electricity, developed laws of electrolysis. Faraday himself was not a proponent of atomism. | |
1859 | J. Plucker | Built one of the first gas discharge tubes ("cathode ray tube"). | |
1869 | Dmitri Mendeleev | Arranged elements into 7 groups with similarproperties.  He discovered that the properties of elements  "were periodic functions of the their atomic weights".  This became known as the Periodic Law. | |
1873 | James Clerk Maxwell | Proposed electric and magnetic fields filled the void. | |
1879 | Sir William Crookes | Discovered cathode rays had the following properties: travel in straight lines from the cathode; cause glass to fluoresce;impart a negative charge to objects they strike; are deflected by electric fields and magnets to suggest a negative charge; cause pinwheels in their path to spin indicating they have mass. | |
1886 | E. Goldstein | Used a CRT to study "canal rays" which had electrical and magnetic properties opposite of an electron. | |
1894 | G.J. Stoney | Proposed that electricity was made of discrete negativeparticles he called electrons ". | |
1895 | Wilhelm Roentgen | Using a CRT he observed that nearby chemicals glowed. Further experiments found very penetrating rays coming from the CRT that were not deflected by a magnetic field. He named them "X-rays". | |
1896 | Henri Becquerel | While studying the effect of x-rays on photographic film, he discovered some chemicals spontaneously...