Tag Archives: Scientists

Dmitri Mendeleev

Dmitri Ivanovich Mendeleev

8 February 1834 – 2 February 1907

BIO

Dmitri Ivanovich Mendeleev was a Russian chemist and inventor. He is best remembered for formulating the Periodic Law and creating a farsighted version of the periodic table of elements. He used the Periodic Law not only to correct the then-accepted properties of some known elements, such as the valence and atomic weight of uranium, but also to predict the properties of eight elements that were yet to be discovered. Mendeleev was born in the village of Verkhnie Aremzyani, near Tobolsk in Siberia. In 1907, Mendeleev died at the age of 72 in Saint Petersburg from influenza.

MENDELEEV’S PERIODIC TABLE

Dmitri Mendeleev is often referred to as the Father of the Periodic Table. He called his table or matrix, “the Periodic System”

I saw in a dream a table where all elements fell into place as required. Awakening, I immediately wrote it down on a piece of paper, only in one place did a correction later seem necessary.

Mendeleev, as quoted by Inostrantzev

Henry Moseley

Henry Moseley

23 November 1887 – 10 August 1915

BIO

Henry Gwyn Jeffreys Moseley was an English physicist, whose contribution to the science of physics was the justification from physical laws of the previous empirical and chemical concept of the atomic number. Henry Moseley was born in Weymouth in Dorset in 1887. Moseley had been a very promising schoolboy at Summer Fields School. In 1906 he won the chemistry and physics prizes at Eton. In 1906, Moseley entered Trinity College of the University of Oxford, where he earned his bachelor’s degree. While an undergraduate at Oxford, Moseley joined the Apollo University Lodge. After graduation from Oxford in 1910, Moseley became a demonstrator in physics at the University of Manchester under the supervision of Sir Ernest Rutherford. Moseley was shot and killed during the Battle of Gallipoli on 10 August 1915, at the age of 27.

MOSELEY’S LAW

Moseley discovered a systematic mathematical relationship between the wavelengths of the X-rays produced and the atomic numbers of the metals that were used as the targets in X-ray tubes. This has become known as Moseley’s law.

Moseley’s experiments in X-ray spectroscopy showed directly from their physics that cobalt and nickel have the different atomic numbers, 27 and 28, and that they are placed in the Periodic Table correctly by Moseley’s objective measurements of their atomic numbers. Hence, Moseley’s discovery demonstrated that the atomic numbers of elements are not just rather arbitrary numbers based on chemistry and the intuition of chemists, but rather, they have a firm experimental basis from the physics of their X-ray spectra.

John Newlands

Johann Wolfgang Dobereiner

26 November 1837 – 29 July 1898

BIO

John Alexander Reina Newlands was a British chemist who worked concerning the periodicity of elements. Newlands was born in London in England, at West Square in Lambeth, the son of a Scottish Presbyterian minister and his Italian wife. Newlands was the first person to devise a periodic table of chemical elements arranged in order of their relative atomic masses. John Newlands died due to complications of surgery at his home in Lower Clapton, Middlesex and was buried at West Norwood Cemetery. His business was continued after his death by his younger brother, Benjamin.

LAW OF OCTAVES

He published in 1865 his ‘Law of Octaves’, which stated that ‘any given element will exhibit analogous behaviour to the eighth element following it in the table. Newlands arranged all of the known elements, starting with hydrogen and ending with thorium (atomic weight 232), into eight groups of seven, which he compared to octaves of music. Groups were shown going across the table, with Periods going down – the opposite from the modern periodic table.

Johann Wolfgang Dobereiner

Johann Wolfgang Dobereiner

13 December 1780 – 24 March 1849

BIO

Johann Wolfgang Döbereiner was a German chemist who is best known for work that foreshadowed the periodic law for the chemical elements, and for inventing the first lighter, which was known as the Döbereiner’s lamp. He became a professor of chemistry and pharmacy at the University of Jena.

DOBEREINER’S TRIADS

In the history of the periodic table, Döbereiner’s triads were an early attempt to sort the elements into some logical order by their physical properties. In 1817, a letter reported Johann Wolfgang Döbereiner’s observations of the alkaline earths; namely, that strontium had properties that were intermediate to those of calcium and barium. By 1829, Döbereiner had found other groups of three elements whose physical properties were similarly related. He also noted that some quantifiable properties of elements (e.g. atomic weight and density) in a triad followed a trend whereby the value of the middle element in the triad would be exactly or nearly predicted by taking the arithmetic mean of values for that property of the other two elements.