Historical Development of Atomic StructureYazan FahmawiSept. 30, 1995 T 3 IBS Chemistry Ms. Redman The idea behind the 'atom' goes back to the Ancient Greek society, where scientists believed that all matter was made of smaller, more fundamental particles called elements. They called these particles atoms, meaning 'not divisible.' Then came the chemists and physicists of the 16 th and 17 th centuries who discovered various formulae of various salts and water, hence discovering the idea of a molecule. Then, in 1766 was born a man named John Dalton born in England.

He is known as the father of atomic theory because he is the one who made it quantitative, meaning he discovered many masses of various elements and, in relation, discovered the different proportions which molecules are formed in (i. e. for every water molecule, one atom of oxygen and two molecules of hydrogen are needed). He also discovered the noble, or inert gases, and their failure to react with other substances. In 1869 a Russian chemist, best known for his development of the periodic law of the properties of the chemical elements (which states that elements show a regular pattern ('periodicity') when they a rearranged according to their atomic masses), published his first attempt to classify the known elements. His name was Mendeleyev, and he was a renowned teacher.

Because no good textbook in chemistry was available at the time, he wrote the two-volume Principles of Chemistry (1868-1870), which later became a classic. During the writing of this book, Mendeleyev tried to classify the elements according to their chemical properties. In 1871 he published an improved version of the periodic table, in which he left gaps for elements that were not yet known. His chart and theories gained acceptance by the scientific world when three elements he 'predicted'-gallium, germanium, and scandium-were subsequently discovered In 1856 another important figure in atomic theory was born: Sir Joseph John Thomson.

In 1906, after teaching at the University of Cambridge and Trinity University in England, he won the Nobel Prize in physics for his work on the conduction of electricity through gases. He discovered what an electron is using cathode rays. An electron is the smallest particle in an atom, whose mass is negligible compared to the rest of the atom, and whose charge is negative. Though scientists did not know it at the time, electrons were located in an electron cloud rotating around the nucleus, or center of the atom.

Another prominent figure in nuclear physics is a man called Ernest Rutherford, born in 1871. He also was a professor at the University of Cambridge, the University of Manchester (both of which are in England), and at McGill College in Montreal, Canada. His importance comes after the discovery of radioactivity in 1896 by a French scientist named Becquerel. Rutherford identified the three main components of radioactivity: alpha, beta, and gamma particles.

He also found the alpha particle to be a positively charged helium atom. Also, Rutherford was the first one to discover the true structure of an atom, it having a central, heavy nucleus with an electron cloud surrounding it. It was Rutherford that, through experiments such as passing alpha particles through a thin gold foil and watching some repel, discovered the second constituent of the atom (also the first component of the nucleus): the proton. The proton has a relative atomic mass of one and has a positive charge. Rutherford also went down in history as the first man to artificially cause a nuclear reaction when, in 1919, he bombarded nitrogen gas with radioactive alpha particles, which resulted in atoms of an oxygen isotope and protons. A unit of radioactivity, the rutherford, was named in his honor.

A colleague of Rutherford's at Cambridge University was a man named James Chadwick discovered the third fundamental particle that makes up the atom: the neutron. This discovery led immediately to the discovery of nuclear fission and the atom bomb The neutron has a relative atomic mass of one, and has no positive or negative charge (i. e. it is neutral). It is found in the nucleus of atoms, along with the proton. Chadwick was one of the first British scientists to stress the development of a possible atom bomb.

His name was strongly associated with the British atomic bomb effort, especially during World War II. During the last two years of W. W. II (1943-1945) Chadwick moved to New Mexico, where he spent much of his time researching at the Los Alamos Scientific Laboratory, a site chosen by the US government for nuclear weapon research.

The first atomic bomb was developed here with the help of James Chadwick. Chadwick earned the Nobel Prize for physics in 1935. In the same era of the development of the atom lived a man, just across the North Sea from these three learned individuals, in Denmark. Neil's Henrik Bohr, born in 1885, was also a considerable man when it came to nuclear and atomic physics. He moved to Cambridge University in 1911, working under J. J.

Thomson, but soon moved to Manchester to work under Rutherford's supervision. He won the Nobel Prize in physics in 1922 for his theory on atomic structure (also known as the Quantum Theory), which was published in papers between 1913 and 1915. He based his workaround Rutherford's conception of the atom. This theory, that suggests that electrons only emit electromagnetic energy when they jump from one quantum level to another, contributed tremendously to future developing of theoretical atomic physics. His work helped lead to the notion that electrons exist in shells and that the electrons in the outermost shell certify an atom's chemical properties. He later illustrated that uranium-235 is the singular isotope of uranium that undergoes nuclear fission.

The Bohr moved to England, and then to the US, where Bohr went to work for the government at Los Alamos, New Mexico, along with James Chadwick, until the first bomb's detonation in 1945. He disapproved complete secrecy of the nuclear bomb, and believed that its consequences would revolutionize the modern world. He wanted some sorts of international law to watch over the use of nuclear devices. In 1945 Bohr returned to the University of Copenhagen in Denmark, where he began developing peaceful uses for atomic energy, such as power plants using nuclear resources as opposed to fossil fuels such as coal, oil, and natural gases. Bohr died in Copenhagen on November 18, 1962. In Austria in 1887 a man by the name of Erwin Schr " odin ger was born.

He became a physicist best known for his mathematical studies of the wave mechanics of orbiting electrons. His most famous and important contribution to the understanding of atomic structure is a meticulous and precise mathematical description of the standing waves orbiting electrons follow. His theory was published in 1926, and along with a German physicist's theory of matrix mechanics, their theories became the basis of quantum mechanics. Schr" the 1933 Nobel Prize in physics with the British physicist Paul A.

M. Dirac for his contribution to the development of quantum mechanics. Through the centuries that have passed, minds have been boggled, countless questions have been answered, and many great minds conceived, however, there is no doubt that there is still much to discover about the atom, such as sub-atomic, elementary particles. A whole new generation of great scientists is still to come, to explore and unlock the universe's secrets.