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]The periodic table is one of the most relevant successes of the chemistry, because allows to understand the development of chemical atomic properties of an element according to a logic line. All the elements are ordererd by their atomic number ( number of protons) in ascending order. A table so constituted is called Periodic Table of Elements.

The need to classify the knowledges about elements had been already felt in 1789, when Lavoiser suggested a example of rudimental element table. The modern periodic table had been realized before the subatomic particles discover and the quantum physic formulation. In 1829 the German chemist Johann Wolfgang Dobereiner noticed that,if the elements are arranged in order of increasing atomic number, by inserting after other properties, you can see a ripple or a periodicity of these properties as a functio]n of atomic number of the element. In this way, Dobereiner noticed a certain amount of triads, groups of three elements with these similarities.

It was at this time that Meyer and Mendeleev (independently) assumed the atomic weight as a parameter to the periodic classification of the elements, which was a decisive step towards the more refined concept of atomic number. Meyer published his results a few months after Mendeleev, and this is that very often it refers to the periodic table of elements with only the name of the latter. He also suggested that there were other factors not currently known, occupying the empty cells of the table, he found confirmation of theory with the discovery of the electronic structure of the elements in the late nineteenth and early twentieth century.

The periodic table is divided into four different blocks: s, p, d and f, whose name results from the type of occuped atomic orbital with Aufbau principle.  A group is a vertical column in the periodic table. Groups are considered the most important method of classifying the elements. In some groups, the elements have very similar properties and exhibit a clear trend in properties down the group, such as, the firts one which is made up very reactive elements (alkalis), or the last one (the 18th), constituted by non-reactive gases (noble gases). A period is a horizontal line in the periodic table: periods are equal the first quantic number ( first quantic number describes the energy level of the electron) of the atom valence strate.

In a table so done, it's easy to forsee a chemical feature of an element: in fact, you can well see that atomic radius ( half distance between two atom centre in a molecule) increase along the groups and decrease along the periods.

Instead, ionization energy ( minimum energy needed to expulse an electron from foundamental state of a atom in gas state), electronegativity (Atomic attitude to attract bond electron) and electron affinity ( energy released when an electron is added to an atom or ion in gas phase) increase along the periods but decrease along groups.

Now, you can watch feature of elements in the table thanks a new album in Save the Earth! The work is now in programming, but you can always view the last tabels! Good fun!

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