Which element has the ordinal number 4
The Periodic table of the elements (short Periodic table or PSE) represents all chemical elements with increasing nuclear charge (atomic number) and according to their chemical properties divided into periods as well as main and subgroups.
Today, the periodic table is primarily used to provide an overview. Historically, it was of particular importance in predicting the discovery of new elements and their properties.
The following is the periodic table in its most well-known form today as the long-period table:
- The elements are listed with their atomic number and their symbol.
- As Periods the horizontal lines or rows are designated,
- as groups the vertical columns.
- The Peel refer to Niels Bohr's atomic model.
(A periodic table extended by atomic number 118 can be found under Extended Periodic Table.)
Structure in detail
All matter around us is made up of atoms.
- Every atom consists of an atomic nucleus and an electron shell.
- Each atomic nucleus contains positively charged protons (at least one, at most a little more than 100), the number of protons is referred to as the "atomic number" and serves as the "atomic number" (OZ) for the type of atom in question.
- Each atomic nucleus is surrounded by an electron shell. If this shell contains exactly as many (negatively charged) electrons as there are protons in the associated nucleus, the atom is in the "electrically neutral" state, since the opposing electrical charges of protons and electrons are equal.
- The "periodic table" only refers to atoms in this electrically neutral state.
- Electrons can only be found in the atom on such orbits that are certain distances from the atomic nucleus; The term “shell” is also used for such paths belonging to a distance.
- Each of these shells only offers space for a very specific number of electrons:
- Only two electrons fit into the innermost shell, so there are only two chemical elements that only have this innermost electron shell, those are those with the first two atomic numbers: 1 (hydrogen) and 2 (helium). They therefore form the top row in the representation of the periodic table.
- In the next atom with three protons and consequently three electrons, the third electron is individually located in an electron shell further out (lithium with atomic number 3). This next shell has space for a maximum of eight electrons. According to this structure, these eight elements (with a total of three to ten electrons) are shown as the next row in the periodic table. At the atomic number 11 (sodium) another electron shell is started and occupied with an electron, here again there is space for a maximum of eight electrons; thus the elements up to atomic number 18 (argon) also form the next following row (line) in the representation in the periodic table.
- If one only considers the electrons of the respective outermost shell, one speaks of the outer electrons; There are one or two outer electrons in the innermost shell, and one to eight outer electrons in the next two. If you compare the material properties of elements with the same number of outer electrons (or their chemical compounds with any other element), you will find many matches that are based precisely on the fact that they are elements with the same number of outer electrons. So are z. B. the elements with only the first of eight outer electrons are alkali metals, the elements with seven outer electrons are halogens and those with fully filled electron shells are noble gases. The outer electrons essentially determine the chemical properties and they repeat themselves periodically, which has led to the representation of the elements in rows and their naming with the term "period". The elements that are similar to one another are listed in the periodic table and each form a "group"; this also applies to the other elements below; the columns discussed so far are the main groups.
- This structure of the structure is interrupted in the higher periods. In the next two periods, the first two electrons also form a new outer shell; However, before the third to eighth electrons are added, a new electron shell underneath is formed and filled with ten places (OZ 21 to 30 and 39 to 48); Elements here below one another are called subgroups.
- In the two following periods, an even deeper (third outermost) bowl with 14 places is created (OZ 57 to 71 and 89 to 103); the installation of the additional electrons in such deeply lying shells leads - as expected - to the fact that these elements are also very similar to one another.
- Every atomic nucleus - except for the hydrogen isotope 1H - contains electrically uncharged neutrons, which, however, play no role in the structure of the periodic table. They are shown in the “Isotope Table” (and details on each nuclide in the “List of Isotopes”).
- Since the electrons only have a negligibly small proportion of the total mass, only the mass of the protons and neutrons together is decisive for the atomic mass; the latter (formerly called “atomic weight”) is often given in periodic tables, but is also irrelevant for its structure.
Additional information in the PSE
In the periodic table you can see that some properties of the elements can be found or represented in certain positions and areas in the periodic table and in the periodic table:
- Mass - increases from top to bottom and from left to right (exceptions: Ar before K, Te before I, Co before Ni, Th before Pa)
- Atomic radius - increases from top to bottom, from left to right (for main group elements)
- Electronegativity - decreases from top to bottom, increases from left to right (exception: noble gases)
- Ionization energy - decreases from top to bottom, increases from left to right
- Metal character - increases from top to bottom, decreases from left to right
- Basicity of the oxides - increases from top to bottom, from left to right decreases
- Oblique relationships:
- Lanthanide contraction
The radioactive elements are marked as additional information that has nothing to do with the electron configuration and therefore with the position in the PSE:
Element 82 (lead) is the last element that is still stable - i.e. not radioactive. All of the following (atomic number 83 and higher) are without exception radioactive and therefore unstable. 83 (bismuth) is a special or borderline case with an extremely long half-life. Elements 1 to 82 also contain two substances that are radioactive, i.e. unstable: 43 (technetium) and 61 (promethium). This actually leaves only 80 stable elements that occur in nature - all others are radioactive elements. Of the radioactive elements, only bismuth, thorium and uranium are found in nature in large quantities, since these elements have half-lives in the order of magnitude of the age of the earth or longer. With the exception of one isotope of plutonium, all other radioactive elements are either intermediate decay products of the four radioactive decay series, such as radium, or arise from rare natural nuclear reactions or from spontaneous splitting of uranium and thorium. Elements with ordinal numbers above 94 can only be produced artificially; although they are also formed during element synthesis in a supernova, due to their short half-lives, no traces of them have yet been found in nature.
See also: Development of the Periodic Table of the Elements
The dating of the discovery of such chemical elements, which have been known since prehistoric times or antiquity, is only imprecise and, depending on the literature source, can vary by several centuries. More reliable dating is only possible from the 18th century. Until then, only 15 elements were known and described as such (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 and scientifically described in the 19th century. At the beginning of the 20th century only ten of the natural elements were unknown. Since then, mainly difficult to access, often radioactive elements have been shown. Many of these elements do not occur naturally and are the product of man-made nuclear fusion processes. It was not until December 1994 that the two artificial elements Darmstadtium (Eka-Platin) and Roentgenium (Eka-Gold) were produced.
At the beginning of the 19th century, Johann Wolfgang Döbereiner first established a connection between atomic mass and the chemical properties of individual elements. In 1863 Newlands set up a table of the elements in groups of eight (law of octaves) arranged according to atomic mass. The periodic table itself was drawn up in 1869 almost simultaneously and independently of one another by Dmitri Mendeleev (1834–1907) and Lothar Meyer (1830–1895). They also arranged the chemical elements according to increasing atomic mass, whereby they arranged elements with similar properties (number of valence electrons) one below the other. In the 20th century the structure of atoms was discovered, the periodicity was explained by the structure of the electron shell.
Help to memorize
A possible help in memorizing the main group elements are these sentences:
- „Liebe Berta, B.itte C.ome Nie Ohne F.rish Nolken! "
Sorted by period in the periodic table. Knowledge of the atomic symbols is assumed.
According to main groups:
- „Hallo Liebe N / Adine Kcould you R.abeC.hemischesFr.agen. "
The artificial elements 113-118 are not taken into account here.
Periodic Table of the Explorers
The periodic table gives an overview of the discoverers or producers of the individual elements, provided they are known.
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