Oxidation numbers periodic trends

In general, the farther left an element is in the periodic table, the more likely it is that the atom will be "cationlike." Metals, therefore, usually have positive oxidation numbers. The farther right an element is in the periodic table, the more likely it is that the atom will be "anionlike." Nonmetals, such as O, N, and the halogens, usually have negative oxidation numbers. We ll see the reasons for this trend in Sections 63-6.5. 

The outermost electrons, often called the valence electrons, are primarily responsible for the chemical properties of the elements. It follows that the elements in a specific group will show similar characteristic oxidation numbers (charges, also called valences) and display a trend in characteristics. Even though electron configurations were not known when the earliest periodic tables were formulated, the elements were placed by similarity of characteristics. 

The immense number of chemical compounds formed by the halogens provides chemists with an extraordinary database from which numerous chemical and physical phenomena can be correlated with respect to various periodic trends. From databases like Inorganic Crystal Structure Data (ICSD, http //www.fiz-karlsruhe.de ) and International Centre for Diffraction Data (ICDD, http //www.icdd.com) with 67 000 and 25 000 entries, respectively, one can easily make out that halides are one of the dominant classes of compounds besides oxides. Even within the subset of inorganic solids, there is tremendous diversity of composition, stracture, and properties and to summarize this would create its own encyclopedia. Therefore, the discussion in this article is limited primarily to binary halides, their structures, and some of their properties, except halides of elements which are nonmetals. Binary actinide hahdes are discnssed elsewhere see Actinides Inorganic Coordination Chemistry). Complex hahdes (sohd phases containing two or more kinds of metal ions), ... 

Since so much can be predicted or at least rationalized on the basis of the periodicity of a few simple atomic properties, especially Pauling electronegativity, size, and charge (or oxidation number) see Oxidation Number) of the atoms or ions involved, we begin by looking at these trends in some detail (beyond that done in General Chemistry courses) and... 

The concept of an atom s oxidation state see Oxidation Number) can provide fundamental information about the stmcture and reactivity of the compound in which the atom is found. In fact, it can be argued that oxidation states provided the basis for Medeleev s initial organization of the periodic table. For the main group elements, the relative stability of lower oxidation states within a given group increases as the atomic number increases. This trend in the periodic table see Periodic Table Trends in the Properties of the Elements) is generally attributable to the presence of an inert s pair see Inert Pair Effect) caused by relativistic effects see Relativistic Effects). 

Oxidation numbers are assigned to elements to name inorganic compounds, to keep track of electrons in electron transfer (oxidation-reduction) reactions, and to explore trends in chemical reactivity across the periodic table. 

Which periodic trend is responsible for the observation that the maximum oxidation state of the transition-metal elements peaks near groups 7B and 8B (a) The number of valence electrons reaches a maximum at group 8B. (b) The effective nuclear charge increases on moving left across each period,... 

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