sâmbătă, 6 aprilie 2013


                                              THE WORLD IS MADE?

This was the question that have put her Greek philosophers over 2000 years ago. A piece of metal material, a piece of quartz, a drop of water - can be divided into smaller and smaller pieces but remains the same field.
Filisoful Leocippus (v sec.al century BC) was the first to suggest that everything is composed of identical particles, which he named atoms from the Greek word meaning invisible. theory was developed by his student and disciple Democritus (ca. 460-370 BC) suggested that the constant movement of atoms explain the creation of the universe:groups formed atoms heavier than Earth, while lighter groups formed celestial groups. The greatest scientist of the era, Aristotle (384-322 BC) refused to accept this concept, and his writings have been dominant for over 1500 years.
Atom theory was incorporated into the Roman philosopher long poem Leucretiu (aprox.99 - 55 BC), called De Rerum Natura (On the nature of things).

                 Leucretiu's work was among the first that were printed after the invention of printing in the late fifteenth century, and it affected the thinking of many, including the French philosopher Pierre Ganssendi which in turn influenced the Englishman Robert B. (1627 - 1691 ). Robert's experiments on gas properties suggested that Bemoulli (made calculations that supported him) Robert B. At the same time they develop knowledge of chemistry. First chemists have recognized the existence of elements substances such as metals, that can not be decomposed into other substances - and they realized that chemical compounds are formed in amounts of different elements, but only when chemist Antonie Lavoisier (1743 - 1794) introduced weighing method was accurate chemical reactions set the stage for a theory to explain these reactions.     Even Lavoisier, a list of items that he published in 1789, introduced substances such as limestone and silica, which are composed of two elements.
Perhaps one of the most important findings was confirmation theory mass conservation in chemical reactions: it was a strong support, having its origin in Democritus's original idea that all chemical transformations are only rearrangements of some fundamental units unchangeable. Equally important was the law of constant proportions, stated by French chemist JL
Proust (1754 - 1826), which states that every pure chemical compound contains fixed and constant proportions by weight of its constitutive elements.


Dalton's discovery

            John Dalton was born in 1766 in Eagesfield, near Cockemounth of Cumberland (England), and was educated at the local school Quaqers religious sect.
At the age of only 12 he became a teacher at the school, but in 1781 moved to the nearby town of Kendal, where he remained until 1787, teaching math and stiinte.El began to keep a meteorological diary in 1787, and his first publication was entitled, observations and weather eseurii''
            That same year Dalton moved to Manchester, where he was appointed professor of mathematics and natural philosophy at New College. One of his first works was what is now known as color blindness, which has suffered himself.
When the College moved to New York, he became a,, state and private teacher of mathematics and chemistry.''
Dalton's interest in meteorology led him to conduct experiments with different gas properties and how they dissolve in liquids.
In a paper about gas absorption (1803) he wondered why water does not dissolve the same amount of different gases.
Dalton says, I'm almost convinced that the situation depends on the size and number of particles of different gases. "In recognition of his theories Leocippus and Democritus, Dalton called these particles atoms. Based on its observatories could make calculations of the relative weight of atoms in a number of different compounds - water, ammonia, carbon dioxide, etc. - and here came the idea that all chemical combinations occur between atoms of different weights.
         He presented his theory of Thomas Thompson of the University of Glasgow, who included it in the 1807 edition of his work chemistry system. The next year Dalton published his first part of his paper chemicals new system of philosophy.
Main utterances of Dalton's atomic theory was, first, that matter consists of atoms invisible, secondly all atoms of an element are identical in weight and all other physical properties either whether chemical, thirdly that different elements have different kinds of atoms with different weights in the fourth place, the atoms are indestructible, the chemistry just a rearrangement of atoms, and ultimately a chemical compound containing a defined number of atoms of each element
Although most modern theory believe that atoms are indestructible and they are made up of subatomic particles, Dalton's theory remains the basis of our understanding of chemical reactions.
Modern analytical techniques have made it possible to find the atomic mass of each element, but each element has a atomic number from 1 for hydrogen (the lightest element to over 100 for unstable radioactive elements, which indicate a higher atomic mass and
        John Dalton was elected a Fellow of the Royal Society in 1822.
He lived for over 50 years at Manchester where he continued his work and teaching laboratory.
He rarely went out, his only passion was bowling on Thursday afternoons.