26 nov Periodic Law Elements Definition
Britannica.com: Encyclopedia article on periodic law Although all elements have been discovered up to Oganesson (element 118), the chemistry of elements beyond hassium (element 108) is not well understood. Of these, only copernicium (element 112), nihonium (element 113) and flerovium (element 114) have been the subject of experimental studies; These studies have not yet yielded conclusive results.  Metallic Huge covalent Molecular covalent Simple atoms Unknown Background color shows binding of simple substances in periodic table The last named elements – nihonium (113), moscovium (115), tennessine (117) and oganesson (118) – completed the seventh series of the periodic table.  Future elements are expected to begin an eighth round. These elements can be designated either by their atomic number (e.g. “element 119”) or by the systematic names of IUPAC elements, which refer directly to atomic numbers (e.g. “ununennium” for element 119, derived from the Latin unus “one”, from the Greek ennea “nine” and the traditional suffix -ium for metallic elements).  All attempts to synthesize such elements have so far failed. Since 2018, attempts have been made at the Riken Research Institute in Japan to produce element 119. The Joint Nuclear Research Institute in Russia is also planning its own attempts to synthesize elements from the first period 8.    The early years of the 19th century saw a rapid development of analytical chemistry – the art of distinguishing different chemical substances – and the development of extensive knowledge about the chemical and physical properties of elements and compounds.
This rapid expansion of chemical knowledge soon necessitated classification, as the classification of chemical knowledge is based not only on the systematized literature of chemistry, but also on the art of laboratory, through which chemistry as a living science is transmitted from one generation of chemists to the next. Relationships were more readily recognized between linkages than between elements; As a result, the classification of elements lagged behind that of compounds for many years. In fact, for nearly half a century, no general agreement had been reached among chemists on the classification of elements after compound classification systems had been established in common usage. For example, the valence of an element can be defined either as the number of hydrogen atoms that can combine with it to form a single binary hydride, or as twice the number of oxygen atoms that can combine with it to form a simple binary oxide (i.e. no peroxide or superoxide). The valences of the elements of the main group are directly related to the group number: The hydrides of the main groups 1–2 and 13–17 follow the formulas MH, MH2, MH3, MH4, MH3, MH2 and finally MH. The highest oxides increase in value, according to the formulas M2O, MO, M2O3, MO2, M2O5, MO3, M2O7. [f] The electronic configuration suggests a ready-made explanation of the number of electrons available for bonding, although a full explanation requires taking into account the energy that would be released during the formation of compounds with different valences, rather than simply looking at electron configurations.  Today, the concept of valence has been expanded to include that of the oxidation state, which is the formal charge that remains on an element when all elements of a compound other than their ions have been removed.  Danish physicist Niels Bohr applied Max Planck`s idea of quantification to the atom.
He concluded that the energy levels of the electrons were quantized: only a discrete set of stable energy states was allowed. Bohr then tried to understand periodicity through electron configurations, and in 1913 suggested that internal electrons should be responsible for the chemical properties of the element.   In 1913, he produced the first electronic periodic table based on a quantum atom.  When atomic nuclei are highly charged, a special theory of relativity is needed to estimate the effect of the nucleus on the electron cloud. These relativistic effects cause heavy elements to exhibit increasingly different properties than their lighter counterparts in the periodic table. For example, relativistic effects explain why gold is gold and mercury is a liquid.   These effects are expected to become very strong by the end of the seventh period, which could lead to a collapse in periodicity.  Electronic configurations and chemical properties are only clearly known up to element 108 (hassium), so the chemical characterization of the heaviest elements remains a current research topic.  Helium is a noble gas that is not reactive under standard conditions and has a complete outer shell: these properties are similar to noble gases of group 18, but not at all to the reactive alkaline earth metals of group 2. Therefore, helium is almost universally classified in group 18, which is most consistent with its properties.
 Helium, however, has only two outer electrons in its outer shell, while other noble gases have eight; And it is an element of the S-block, while all other noble gases are elements of the p-block. In addition, solid helium crystallizes in a densely compacted hexagonal structure compatible with beryllium and magnesium of group 2, but not with other noble gases of group 18.  In this way, helium adapts better to alkaline earth metals.   Therefore, tables in which hydrogen and helium float outside all groups are rarely encountered.   Some chemists have advocated the adoption of electronic classification in Group 2 for helium.      Arguments in favor of this are often based on the anomaly trend in the first row, since helium as the first element s2 stands out as anomalous in front of alkaline earth metals in a way that helium as the first noble gas does not.  Many terms have been used in the literature to describe groups of elements that behave similarly. He considered the issue “of considerable importance” to chemists, physicists and students, noting that the variation in the periodic tables published on this point generally confused students and teachers.  This resulted in a preliminary report in 2021 approving lutetium as the first 5d element.
The reasons given were to display all elements in ascending order of atomic number, to avoid fission of the d blocks and to let the blocks follow the widths required by quantum mechanics (2, 6, 10 and 14).  The project ended that year.  Currently, the IUPAC periodic table website still shows the 1988 compromise, but mentions the Group 3 problem and the plan to solve it, writing “Stay tuned.”  For reasons of space, the periodic table is usually represented with the F-block elements cut and positioned as an independent part under the main body.    This reduces the number of element columns from 32 to 18.  Atomic radii (the size of atoms) usually decrease along the main group elements from left to right, as the nuclear charge increases, but the outer electrons are always in the same shell.