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100
440bc The first idea of an atom
The Greek philosopher Democritus introduces that everything is made up of tiny particles. He calls the atoms, from the Greek ‘atomos’ meaning invisible. His theory was ignored for over 2000 years. -
200
330bc Proposal of the 4 element theory
Aristotle proposes the four element theory of earth, air, fire and water -
1778- First extensive list of elements
French man Antoine Lavoisier wrote the first extensive list of elements containing 33 elements and showed differences between metals and non-metals. -
1803- Daltons law
John Dalton re-introduced the idea of tiny particles and called atoms. He says that they cannot be split but can be joined together and make all matters in the universe. Daltons Law states that the total pressure given by the mixture of non-reactive gases is equal to the sum of the partial pressures of individual gases. -
1817- Law of Triads
The german Johann Dobereiner Proposes the law of triads elements exist in threesome or triads, with similar properties. An atmic weight of the middle elements is the average of the other two. -
1864- Dimitri Mendeleev
Dmitri Mendeleev produced a table based on atomic weights but arranged it periodically with elements with similar properties under each other. His Periodic Table included the 66 known elements organized by atomic weights. This formed the basis of the periodic table. -
1864- The first arrangement of atoms by atomic weight
John Newlands arranged the known elements in order of atomic weights and observed similarities between some elements -
1894- The discovery of the noble gases.
The scottsman William Ramsay discovered the noble gases. Noble gases are a group of chemical elements that have very similar properties. the are generally colourless, odorless, monatomic gases thave have very low chemical activity. -
1900- Ernest Rutherford
Ernest Rutherford's atomic theory described the atom as having a central positive nucleus surrounded by negative orbiting electrons. His model showed that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space. Rutherford came to this conclusion following the results of his famous gold foil experiment. This experiment involved the firing of radioactive particles through minutely thin metal foils and detecting them using screens coate
