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500
Leucippus
Leucippus was born in about 500 B.C. and died in 450 B.C.The Greek tradition regarded Leucippus as the founder of atomism in ancient Greek philosophy. Little is known about him and his views are often hard to separate from those of his colleague Democritus.The extent of Leucippus’ contribution to the atomist theory is unknown. His relationship to Democritus, and even his very existence, was a subject of controversy. -
500
Leucippus
He is named, by most sources, the originator of the theory that the universe consists of two different elements, which Leucippus called the ‘full’ or ‘solid’, and the ‘empty’ or ‘void’. Both the void and the solid atoms are thought to be infinite and between them to form the elements of everything.Atoms cannot change or disintegrate into ‘what is not’ and each is a solid unit although the combinations of atoms that form the world of appearance continually alter. -
540
Democritus
Ancient reports state that Democritus was born about 460 BC and died around 370 BC. He is known for his influence on modern science more than any other philosopher. Powerful microscopes aside, Democritus formed his theories from watching decay and mixing elements that are not easily separated once combined (such as water and earth in mud). He also believed that nothing can come from nothing, everything is already in the world and it is merely a matter of combination and re-combination of atoms. -
540
Democritus
Atoms remain inseparable in and of themselves, but are capable to combine to other atoms to make up the materials of life. Democritus also thought that the solidness of any given material was dependent upon the shapes of these atomic bits. He and other ‘atomists’ believed that atoms were inseparable, infinite in size and shape as well as completely solid. -
Jan 1, 616
Aristotle
There were also four qualities: dryness, hotness, coldness and moistness. Each of these elements moves naturally in line to their ‘proper place’.Aristotle’s theory also had two forces: conflict and harmony. Conflict was thought to cause bad things and harmony good things.Aristotle’s theory was used for almost 2000 years, until after the scientific revolution, when other theories were supported. -
Jan 1, 616
Aristotle
Ancient Greek philosopher Aristotle was born around about 384 B.C. and died in 322 B.C.He was a great philosopher and used both inductive and deductive reasoning. Aristotle disbelieved the ancient Greek theory of atoms being of different sizes, regular geometric shapes and being in constant motion. He didn’t think atoms could be in constant motion when in a void.Aristotle developed the theory that all matter consisted of the four elements: Earth, Air, Water and Fire. -
Robert Boyle
Robert Boyle was born on January 25, 1627 and died on December 30, 1691.Boyle mainly studied gases. He discussed the possibility of atoms existing. He proposed that elements are composed of ‘corpuscles’ of various types and sizes that are able to organise themselves into groups that represent different chemical substances.Boyle was also able to tell the difference between a mixture and a compound. This was the image before the atomic theory of matter. -
Antoine Laurent de Lavoisier
Antoine Laurent Lavoisier was born on August 26, 1743 and died on May 8, 1794.One of the most important discoveries of Lavoisier’s was the law of conservation of masses. This law states that the sum of the weight of two chemical substances when combined is equal to the weight of the newly formed compound.This discovery paved the way for the modern theory of atoms.Lavoisier developed his law by conducting another experiment to prove an old theory false. -
John Dalton
John Dalton was born on September 6, 1766 and died on July 26, 1844. He was the first scientist to explain the behaviour of atoms in terms of its weight.Dalton’s fascination with gases gradually led him to prove that every form of matter (whether solid, liquid or gas) was also made up of small individual particles.He introduced his belief that atoms of different elements could be distinguished based on their weights. Dalton also uncovered the fact that atoms couldn’t be created or destroyed. -
John Dalton
He also wrote about his experiments proving that atoms consistently combine in simple ratios. It meant that the molecules of an element are always made up of the same amount, with the exception of water molecules.Dalton’s theory: that the atoms within a given element, are all exactly the same size and weight, while the atoms of different elements look – and are – different from one another. He later invented a table listing the atomic weights of all known elements.His atomic theories were quic -
J.J. Thomson
These particles are now called electrons and this discovery contradicted the prevailing theory that the atom was the smallest fundamental unit.
He suggested a model of the atom as a sphere of positive matter in which electrons are positioned by electrostatic forces.Thomson began studying positive rays, which led to one of his other famous discoveries in 1912. -
J.J. Thomson
Joseph John ‘J.J’ Thomson was born on December 18, 1856 and died on August 30, 1940.His research in cathode rays led to he discovery of the electron and he pursued further ideas in atomic structure exploration.Thomson discovered that all matter is made up of tiny particles that are much smaller than atoms. -
Max Planck
This explained why, for example, a hot iron poker glows red and white.Planck was not trying to revolutionise physics at all but just explain the phenomenon he was studying. -
Max Planck
Max Planck was born on April 23, 1858 and died on October 4, 1947.Planck made many contributions to the theoretical physics, but he is known for his role as the originator of the quantum theory. This theory revolutionised our understanding of atomic and subatomic processes.In 1901 Planck developed a theory that described the experimental evidence that energy did not flow in a steady continuum, but was delivered in separate packets that Planck later called quanta. -
Hantaro Nagaoka
At the time, Nagaoka was the first to defend a Saturnian atomic model where the electrons orbit like Saturn’s rings around the nucleus, which contains a positive electric charge.Thomson, who had discovered the electron, was in favour of the ‘Plum pudding model’. This model described atoms as the electropositive balls that had electrons scattered in them, like fruit in a plum pudding. -
Hantaro Nagaoka
Hantaro Nagaoka was born August 15, 1865 and died on December 11, 1950. Though some atomic models were proposed in the world of physics, it was Nagaoka who was the first to present a Saturnian atomic model.In 1897, new discoveries concerning nuclear physics came on after the other and attention was focused on the structure of the atom. -
Ernest Rutherford
Ernest Rutherford was born on August 30, 1871 and died on October 19, 1937.Rutherford’s investigations into the scattering of alpha rays and the nature of the inner structure of the atom, led to the suggestion of his concept of the ‘nucleus’, his greatest contribution to physics. According to him, practically the whole mass of the atom and all the positive charge of the atom are concentrated in a minute space at the centre. -
Ernest Rutherford
Rutherford was a developer of nuclear physics and the first to split the atom. He was awarded the 1908 Nobel Prize in Chemistry for his theory of atomic structure. Through further experimentation involving firing alpha particles at foil, Rutherford made a discovery that nearly the total mass of the atom is concentrated in a nucleus. In doing so, he gave birth to the nuclear model, a discovery that marked the beginning of nuclear physics and lead the way to the invention of the atom bomb. -
Frederick Soddy
Frederick Soddy was born on September 2, 1877 and died on September 22, 1956.Soddy suggested that the same elements exist in different forms, with nuclei having the same number of protons but different numbers of neutrons. His theory of isotopes explains that different elements can be chemically identical but have different atomic weights and characteristics.Soddy’s theory of isotopes was argued over among scientists until Chadwick’s discovery fo the neutron. -
Erwin Schrödinger
Erwin Schrödinger was born on August 12, 1887 and died on January 4, 1961.His six years in Zurich were among the most productive in his career, though he didn’t begin the work for which he was best known – wave mechanics – until 1925. His interest was sparked by a footnote in a paper by Albert Einstein.Schrödinger began to think about explaining the movement of an electron in an atom as a wave. -
Erwin Schrödinger
By 1926 he published his work, providing a theoretical basis for the atom model that Niels Bohr had suggested based on laboratory evidence. The equation at the heart of his publication became known as Schrödinger’s wave equation. This was the second theoretical explanation of electrons in an atom. -
Henry Moseley
Moseley measured the x-ray spectral lines of nearly all the elements from aluminum to gold. The results of his study showed a clear and simple order of the elements that was based on atomic weights that was then the basis of the Periodic Table.It was Henry Moseley who arranged the Periodic Table in order of the atomic numbers of the elements. -
Henry Moseley
Henry Moseley was born on November 23, 1887 and died on August 10, 1915.Moseley is an English physicist who experimentally demonstrated that the major properties of an element are determined by the atomic number, not by the atomic weight, and confirmed the relationship between atomic number and the charge of the atomic nucleus.Moseley stated there were three unknown elements between aluminum and gold and that there were only 92 elements up to and including uranium and 14 rare-earth elements. -
Niels Bohr
Niels Henrik David Bohr was born on October 7, 1885 in Denmark and died on November 18, 1962 of a stroke.He became an accomplished physicist who came up with a revolutionary theory on the atomic structure.Bohr’s own research led him to theorise a series of articles that atoms give off electromagnetic radiation as a result of electrons jumping to different orbit levels. His ideas formed the basis of future atomic research. -
Niels Bohr
Once Denmark became occupied by Nazi forces, the Bohr family escaped to Sweden then from there Bohr and his son Aage made it to the U.S. where Bohr worked with the Manhattan Project to created the first atom bomb. In 1954, Bohr helped establish a Europe-based particle physics research facility where he put together the Atoms for Peace Conference. He received the Atoms for Peace Award for his theories and efforts to use atomic energy responsibly. -
James Chadwick
In 1932, Chadwick made a discovery in the field of nuclear science: he proved the existence of neutrons – the fundamental particles free of any electrical charge. In contrast with the helium nuclei – or alpha rays – which are charged and therefore repelled by electrical forces present in the nuclei of heavy atoms. Chadwick, in this way, prepared the path towards the creation of the atomic bomb. -
James Chadwick
Sir James Chadwick was born on October 20, 1981 and died on July 24,1974.After the war in 1919, Chadwick returned to England to resume work under Rutherford. Rutherford had succeeded in disintegrating atoms by launching alpha particles at nitrogen with the emission of a proton. This was the first man-made nuclear transformation.Chadwick joined Rutherford in making studies of the properties and structure of atomic nuclei.
