The periodic table is a fascinating system of order that nature has given the elements. The Russian chemist Dimitri Mendelejew and the German chemist Lothar Meyer recognized this almost simultaneously, independently of one another, in the 1860s. Both published their findings in a scientific journal in 1869.
At that time, not all elements were known by a long way, but due to the existing "gaps" in the periodic table, the existence of other as yet undiscovered elements could be predicted. For example, an element "eka-silicon" was postulated, which should be listed under the element silicon in the periodic table. It was a great confirmation of the periodic table when "eka-silicon", which is now called germanium, was later discovered and its chemical and physical properties matched the predictions amazingly well.
Here you can find two explanatory videos on the YouTube channel Knowledgeable Chemistry, in which the periodic table of the elements is clearly illustrated
This video shows the history of the discovery of the periodic table, from antiquity to the artificial elements discovered by the Society for Heavy Ion Research in Darmstadt.
In the periodic table of the elements, all chemical elements are sorted according to increasing atomic number: from hydrogen with the atomic number 1 to the heaviest element known today, the Organesson (atomic number 118). The atomic number, also known as the atomic number, defines the number of protons, the positively charged particles in an atom. So hydrogen has one proton, Organissum has 118 protons. This series of 118 elements is represented in several lines called periods. The elements that are listed below each other in the periodic table, i.e. in one column, form a group. The periodic table has 18 groups, eight of which are called main groups.
According to Bohr's atomic model, an atom consists of a nucleus that contains the positively charged protons and uncharged neutrons and a shell that contains the negatively charged electrons. In the case of an electrically uncharged atom, the number of protons and electrons must always be the same. Since the atomic number and thus the number of protons in the periodic table increase from left to right and from row to row, the number of electrons also increases. According to a very simple, but very helpful idea for understanding the periodic table, the shell of an atom consists of different orbits, also called ?shells?, which can hold different numbers of electrons. These shells lie around the atomic nucleus like the shells of an onion.
In the first period are the lightest two elements hydrogen and helium with one or two protons and electrons. The electrons are located in the innermost shell, which is called the K shell. It cannot accept more than two electrons. In the second period are the elements in which, in addition to the K-shell, the so-called L-shell is also filled with a total of eight electrons, so that the heaviest element of the second period contains a total of ten protons and electrons. In the 3rd period beginning with the element sodium, another shell, the M shell, is filled with eight electrons. The heaviest element of the 3rd period, argon, has 18 protons and electrons and thus the atomic number 18.
From the fourth period a block of 10 subgroup elements with the ordinal numbers 21 to 30 is inserted between the 2nd main group (calcium, ordinal number 20) and the 3rd main group (gallium, ordinal number 31). In this not the outermost shell, as before, but the second outermost shell, which can hold 10 electrons each, is filled. When this shell is completely filled, the outermost shell is filled again from the element gallium onwards. From the sixth period onwards, the block of subgroup elements is subdivided again by inserting 14 elements at a time. In these elements, which are called lanthanoids and actinides, the third outermost shell is filled with 14 electrons each, before the second outermost shell of the subgroups and then the outermost shell of the main group are filled.
The periodic table is now divided in such a way that elements with the same number of electrons in the outermost shell are one below the other and form a group. Since the number of electrons in the outermost shell, the so-called valence electrons, significantly influence the properties of the elements, the elements of a group also have similar properties. This enabled Mendeleev, Meyer and other scientists to predict the existence of as yet unknown elements.
This periodic table, developed by the European Chemical Society, shows the periodic table in a different way. The availability of the element is shown in different colors. The smartphone symbol indicates elements that are built into a standard smartphone and the gray color indicates elements that are obtained under questionable conditions, i.e. in countries where war is raging and / or child labor is common.
last modified: 10.05.2021 16:19 H from