Periodic table

The Periodic Table (Long Version Periodic Table of Elements, abbreviated as PSE ) provides all the chemical elements with increasing nuclear charge (atomic number ) and according to their chemical properties divided into periods, as well as major and minor selcetion It was established in 1869 independently and almost identical to that of two chemists, first of Dmitri Mendeleev, the Russians (1834-1907) and a few months later by the German Lothar Meyer (1830-1895) erected. Historically, the periodic system for the prediction of the discovery of new elements and their properties are of particular importance. Today it serves mainly the overview.

Representation

Below the periodic table is reproduced in its form today known as long-period system:

• The elements are listed with their order numbers and their symbols.
• As periods, the horizontal lines or rows are referred to,
• Groups as the vertical columns.

• One of the atomic number 118 extended periodic table is located under Advanced Periodic Table.
• An image panel is located under Image panel of the chemical elements.

Building in detail

Basics

• Each atom consists of a nucleus and an electron shell.
• Each nucleus contains positively charged protons (at least one, and currently known to 118 ), the number of protons is referred to as atomic number and is used as an order number (OZ ) for the respective atom type.
• Each nucleus is surrounded by an electron cloud. If this envelope contains the same number of (negatively charged ) electrons, such as protons are present in the associated core, the atom is in the electrically neutral state, since the opposite electric charge of the proton and electron are equal.
• The periodic table relates only to the atoms in this electrically neutral - elementary - state.
• Electrons can be in the atom only on those paths which have certain distances from the nucleus; for such a distance corresponding to tracks, the term shell is used. Each of these shells can accommodate only a certain number of electrons.

In the innermost shell only fit two electrons, so there are only two chemical elements that only have this innermost electron shell, that is those with the first two atomic numbers: 1 ( hydrogen) and 2 ( helium). They are therefore in the interpretation of the table, the top row.

In the next atom with three protons and consequently three electrons, the third single electron is in a more outer -shell (lithium with the atomic number 3). This next shell has room for a maximum of eight electrons. These eight elements ( with a total of three to ten electrons ) are shown in the periodic table as the next row corresponding to this structure. When the atomic number 11 (sodium) another electron shell is started and occupied by one electron, here again is for a maximum of eight electrons space; thus form the elements to the atomic number 18 (argon) and the next following row (line ) in the representation of the periodic table.

Considering only the electrons of the outermost shell, then one speaks of the outer electrons; in the innermost shell there are one or two in the next two one to eight outer electrons. When comparing the material properties of elements with the same number of outer electrons (or their chemical compounds, each with any other element ), so there are many similarities that are based precisely that there are elements with the same number of outer electrons. Thus, for example the elements with only the first of eight outer electrons alkali metals, the elements of seven external electron halogens and with a fully filled electron shells noble gases. Thus, the outer electrons largely determine the chemical properties and are repeated periodically, which has led to the appearance of the elements in rows and their designation by the term period. The elements are thus similar to one another in the periodic table with each other and each form a group; This also applies to the other elements in each case below it; in columns discussed so far is the main groups.

This system of construction is interrupted in the higher periods. In the next two periods, although the first two electrons initially form a new outer shell; However, before there comes the third to eighth electron added, an underlying new electron shell is first formed with ten squares and filled (OZ 21 to 30 and 39 to 48); hereunder by side elements are called transition groups.

In the then following two periods even initially results in an even deeper ( third outermost ) shell with 14 seats (OZ 58 to 71 and 90 to 103); the installation of each additional electrons in so deep bowls leads - as expected - to the fact that these elements are also all very similar.

The arrangement of the atoms in the periodic table is thus completely explained by the electron configuration. Notes: Each atomic nucleus, except for the hydrogen isotope 1H, contains electrically uncharged neutrons, but play no role in the development of the periodic table. They are shown in the chart of nuclides as well as the details of each nuclide in the list of isotopes.

Since the mass of the electrons have only a vanishingly small fraction of the total mass, only the mass of the protons and neutrons together is crucial for the atomic mass; latter (formerly called atomic weight ) is often specified in the periodic systems, but plays for the construction of which also does not matter.

Additional information on the PSE

Some properties of the elements can be in certain positions and areas of the periodic table find or predict with him:

• Mass - increases from top to bottom and from left to right (except Ar before K, Te ago I, Co before Ni Th before Pa)
• Atomic radius - increases from top to bottom, from left to right (by main group elements )
• Electronegativity - increases from top to bottom, from left to right (except noble gases )
• Ionization energy - decreases from top to bottom, from left to right to
• Metal character - increases from top to bottom, from left to right
• Basicity of the oxides - increases from top to bottom, from left to right
• Angular relations: Similarities between: Lithium - Magnesium and beryllium - aluminum, boron - silicon
• Grimm shear Hydridverschiebungssatz

As additional information, but have nothing to do with the electron configuration and therefore with the position in the periodic table, the radioactive elements are identified:

The element 82 ( Lead) is the last element that exist from the stable, ie non-radioactive isotopes. All of the following (atomic number 83 and higher) are all radioactive and thus unstable. It is 83 ( bismuth) is a special case or borderline case with an extremely long half-life. Within the elements 1-82 two substances are present, which are radioactive, that is unstable: 43 ( technetium ) and 61 ( promethium ).

So actually remain only 80 stable elements that occur in nature - all others are radioactive elements. Of the radioactive elements only bismuth, thorium and uranium are present in large quantities in nature, since these elements have half-lives on the order of the age of the Earth or longer. All other radioactive elements up to an isotope of plutonium either as radium intermediate decay products of the three natural radioactive decay series or arise in rare natural nuclear reactions or by spontaneous fission of uranium and thorium. Elements with atomic numbers above 94 can only be produced artificially; although they also occur in the synthesis of elements in a supernova, were found due to their short half-lives, up to now no traces of them in nature.

History

The dating of the discovery of such chemical elements that have been known since the early days or antique is only imprecise and may vary depending on the literature source to several centuries. Safer dating is possible only from the 18th century. Hitherto had only 15 elements known as such and described ( metals, such as iron, copper, lead, bismuth, arsenic, zinc, tin, antimony, platinum, silver, mercury and gold or non-metals such as carbon, sulfur and phosphorus).

Most of the elements were discovered in the 19th century and described scientifically. At the beginning of the 20th century, only ten of the natural elements were unknown. Since then, especially difficult to access, often represented radioactive elements. Many of these elements do not occur in nature and are the product of artificial nuclear fusion processes. Only in December 1994, the two artificial elements were Darmstadium ( eka- platinum) and Roentgenium made ​​( eka- gold).

Beginning of the 19th century, Johann Wolfgang Dobereiner introduced for the first time established a link between the atomic mass and the chemical properties of individual elements. Alexandre -Emile de Béguyer Chancourtois developed in 1862 a three-dimensional representation, where he helically arranged the elements according to increasing atomic weights on a cylinder. 1863 presented John Alexander Reina Newlands an ordered according to atomic mass table of the elements in groups of eight ( law of octaves) on. The periodic table itself was erected in 1869 almost simultaneously and independently by Dmitri Ivanovich Mendeleev ( 1834-1907 ) and Lothar Meyer ( 1830-1895 ). In this case also, the chemical elements arranged according to increasing atomic masses, being ruled elements with similar properties (number of valence ) with one another. In addition, attempts were made by Heinrich Adolph tree Hauer and Julius Quaglio, spiral represent the system. In the 20th century the structure of atoms was discovered, the periodicity was explained by the structure of the electron shell.

Periodic Table of the discoverers

This periodic table is an overview of the explorers and producers of each item by clicking on the elements ID. For the elements for which no explorer / producer is known, the current historical knowledge among the general plan is summarized here.

• C: Already known since prehistoric times.
• S: Since prehistoric times, known to be an element of character was probably first recognized by Lavoisier.
• Zn: since about 1300 BC processed in China.
• Sb: Recent discoveries prove the use of antimony by the peoples of Mesopotamia 4,000 years ago.
• Hg: Approximately been known for 3000 years.
• Np - UUO: The persons specified as the discoverer of transuranic elements here are each representative of the participating research groups at the Joint Institute for Nuclear Research in Dubna, at the Lawrence Berkeley National Laboratory in Berkeley, at CERN in Geneva and at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt.

Alternative periodic tables

The shape of the periodic table of Dmitri Mendeleev has prevailed. Nevertheless, were (and are ) there any other suggestions for alternative orders of the elements according to their properties.

Flowers periodic table.

Spatial periodic table.

Periodic Table of Zmaczynski and Bayley.

A pyramid- shaped manner ordnets periodic table.