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Discovery of phosphorus.
Hennig Brand attempted to created a Philosopher’s Stone; an object that could turn metals into gold. He heated residues from boiled urine, and a liquid dropped out and burst into flames. This was the first discovery of phosphorus. -
hosphorus became public.
Robert Boyle also discovered phosphorus, and it became public. -
Johann Dobreiner
The development of the periodic table begins with German chemist Johann Dobereiner (1780-1849) who grouped elements based on similarities. -
47 elements
In 1809 at least 47 elements were discovered, and scientists began to see patterns in the characteristics. -
Law of the triads
Dobereiner proposed the Law of Triads: Middle element in the triad had atomic weight that was the average of the other two members. -
John Newlands
In 1863 English chemist John Newlands divided the than discovered 56 elements into 11 groups, based on characteristics. -
Law of Octaves
he wrote a paper proposing the Law of Octaves which was elements exhibit similar behavior to the eighth element following it in the table. -
Dimitri Mendeleev
Dimitri Mendeleev started the development of the periodic table. He arranged chemical elements by atomic mass. He predicted the discovery of other elements, and left spaces open in his periodic table for them. -
Elements by atomic weights
Then in 1869, Russian chemist Dimitri Mendeleev proposed arranging elements by atomic weights and properties. Mendeleev's periodic table of 1869 contained 17 columns with two periods of seven elements each followed by two nearly complete periods. -
Radioactivity
Antoine Bequerel first discovered radioactivity. Ernest Rutherford named three types of radiation; alpha, beta and gamma rays. Marie and Pierre Curie started working on the radiation of uranium and thorium, which lead to the discoverey of radium and polonium. They discovered that beta particles were negatively charged. -
Henry Moseley
He performed x-rays on know elements. He was able to see the realtionship between x-ray frequency and number of protons.
When Moseley arranged the elements according to increasing atomic numbers and not atomic masses, some of the gaps in Mendeleev's table were taken out. The modern periodic table is based on Moseley's Periodic Law. -
Noble gases
In 1894 Sir William Ramsay and Lord Rayleigh discovered the noble gases, which were added to the periodic table as group 0. -
Discoverey of electrons
J. J. Thomson first discovered electrons. John Townsend and Robert Millikan determined their exact charge and mass. -
Electrons and beta particles
Bequerel discovered that electrons and beta particles which were identified by the Curies are the same thing. -
Break down of atoms
Rutherford announced that radioactivity is caused by the breakdown of atoms. -
Nobel Prize
In 1906, Mendeleev came within one vote of receiving the Nobel Prize in chemistry. -
Electrons orbit
Rutherford and German physicist Hans Geiger discovered that electrons orbit the nucleus of an atom. -
Orbital
Bohr discovered that electrons move around a nucleus in energy called orbitals. Radiation is emitted during movement from one orbital to another. -
Protons in the atomic nucleus
Rutherford first identified protons in the atomic nucleus. He also transmutated (an act that changes the form or character or substance of something) a nitrogen atom into an oxygen atom for the first time. English physicist Henry Moseley provided atomic numbers, based on the number of electrons in an atom, rather than based on atomic mass. -
Neutrons and Isotopes
James Chadwick first discovered neutrons, and isotopes were identified. In that same year Cockroft and the Walton first split an atom by bombarding lithium in a particle accelerator, changing it to two helium nuclei. -
Lanthanides and actinides
Glenn Seaborg identified lanthanides and actinides, which are usually placed below the periodic table. -
60 elements
By 1860 about 60 elements were known.
