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Democritus (400 BC)
Democritus was a Greek philosopher. He lived from 460 BC to 370 BC. Democritus discovered that atoms: are in all forms of existence such as a solid or liquid, they are inseparable, they come in many different sizes and that they are present in the atmosphere.Many people knew him as ‘the father of modern science’. And some even knew him a Democritus of Abdera. -
Joseph Priestley (1774)
Joseph Priestley was an English philosopher. He lived from 1733 to 1804.Priestley begun to research on the nature and properties of gases in the 1770’s. Priestley started to examine all the “airs” that could be released from different substances, he wanted to find all their properties and discover more on their nature. Priestley’s idea was that air is a compound of phlogiston and an acid. He first thought that this acid was "marine acid." It is now called nitrous acid. -
Antoine Lavoisier (1777)
Antoine Lavoisier was a French chemist; he was known as “the father of modern chemistry”. He lived from 1743 to 1794.Lavoisier discovered that atoms: could have two or more parts, have weight or mass.Lavoisier stated the first version of the law of conservation of mass, recognized and named oxygen and hydrogen. He also established the phlogiston theory and helped construct the metric system. He also discovered that, although matter may change its form or shape, its mass always remains the same -
John Dalton (1803)
John Dalton was an English chemist, meteorologist and physicist. He lived from 1766 to 1844. He discovered that all matter is composed of atoms and that different elements have different types of atoms. He also discovered that atoms: could be identified by their differences in weight, they cannot be made or destroyed, all atoms of the same element are identical and that chemical reactions occur when atoms are rearranged. -
Robert Brown (1827)
Robert Brown was a Scottish biologist. He lived from 1773 to 1855. He discovered the jerking movement of microscopic particles only visible under a high-powered microscope. He also discovered this by placing pollen grains in clear water. He established that the tiny particles of inorganic materials such as carbon and metals are also part of the Brownian motion. Browns discovery show that matter is composed of small particles that move in random motion. -
Dmitri Ivanovich Mendeleev (1869)
Dmitri Ivanovich Mendeleev was a Russian chemist and an inventor. He lived from 1834 to 1907.He arranged elements into 7 groups with similar properties, this was the start of the Periodic Table. He discovered that the properties of elements “were periodic functions of their atomic weights”. This then became known as the Periodic Law.The Periodic Table was compiled on the basis of arranging the elements in ascending order of atomic weight and grouping them by similarity of properties. -
William Crookes (1873)
William Crookes was a British chemist and physicist. He lived from 1832 to 1919. He researched electrical dischargers and observed the dark space around the cathode. William Crookes was able to determine the atomic weight of the new element in a research. He also demonstrated that cathode rays travel in straight lines and produce phosphorescence and heat when they strike certain materials. William Crookes was able to invent many different ways to help us study the behaviour of cathode rays. -
Wilhelm Conrad Röntgen (1895)
Wilhelm Conrad Röntgen was a German physicist. He lived from 1845 to 1923.He got his wife to put her hand in the path of the rays over a photographic plate. By doing this he observed an image of his wife's hand, which showed the shadows thrown by the bones of her hand and that of a ring she was wearing. This was the first "röntgenogram" ever taken. -
Albert Einstein (1900)
Albert Einstein was a German scientist; he lived from 1879 to 1995. Einstein was considered as one of “the fathers of modern atomic theory”.One of his theory’s included the formula E=mc2, meaning energy equals mass times the velocity of light squared, which became the cornerstone of atomic theory research. He was able to theorize the presence of electrons that are produced when a beam of light is directed onto the surface of metal, this is now known as the photoelectric effect. -
Richard Abegg (1904)
Richard Abegg was a German chemist. He lived from 1869 to 1910. He had an idea of valence theory to help describe chemical bonding. His rule was a chemistry rule, each element has two valences: a normal valence and a contra valence; the maximum positive and negative valence of and element is equivalent to eight. He stated that there must be eight electrons in the outer shell of an atom so that it gives the most stable configuration and it has been shown to be true of the second principal shell. -
Robert Andrews Millikan (1910)
Robert Andrews Millikan was an American physicist. He lived from 1868 to 1953.Robert A. Millikan was able to determine the charge carried by an electron, using the elegant "falling-drop method". He also demonstrated the atomic structure of electricity. Robert A. Millikan helped verified experimentally Einstein's all-important photoelectric equation. After the discovery of his law of motion of a particle falling towards the earth after entering the earth's atmosphere. -
Ernest Rutherford (1911)
Ernest Rutherford was a British chemist and physicist. He lived from 1871 to 1937 and was known as ‘the father of nuclear physics.' He discovered that the atom has a central positive nucleus surrounded by negative electrons the orbit the central positive nucleus. He suggested that the mass of an atom was contained in the small nucleus leaving the rest of the atom empty space. Rutherford atomic model described that the atom is a tiny, dense, positively charged core called a nucleus. -
Henry Gwyn Jeffreys Moseley (1913)
Henry Gwyn Jeffreys Moseley was an English physicist. He lived from 1887 to 1915.Henry G. J. Moseley helped make some adjustments from physical laws of the previous empirical and chemical concept of the atomic number. He published the Moseley’s Law in 1913. It correlated wavelength and atomic number, therefore demonstrating the importance of atomic number over atomic weight, as this became the common belief. -
Niels Bohr (1913)
Niels Bohr was a Danish physicist. He lived from 1885 to 1962. He was one of the most influential scientists in 20th century. He applied quantum theory to Rutherford's atomic structure by assuming that electrons travel in stationary orbits defined by their angular momentum. This then led to the calculation of possible energy levels. In his model it has a small, positively charged nucleus orbited by negatively charged electrons. -
Sir James Chadwick (1932)
Sir James Chadwick was an English physicist. He lived from 1891 to 1974. He made an amazing discovery in the domain of nuclear science: he proved the existence of neutrons - elementary particles devoid of any electrical charge. He also discovered that β -rays (electrons) are emitted in a continuous spectrum. The neutrons were in contrast with the helium nuclei (alpha rays) which are charged, and therefore repelled by the considerable electrical forces present in the nuclei of heavy atoms.
