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This table lists only the occurrences in compounds and complexes, not pure elements in their standard state or allotropes. Noble gas +1 Bold values are main oxidation states
Oxidation states are unitless and are also scaled in positive and negative integers. Most often, the Frost diagram displays oxidation state in increasing order, but in some cases it is displayed in decreasing order. The neutral species of the pure element with a free energy of zero (nE° = 0) also has an oxidation state equal to zero. [2]
The number indicates the degree of oxidation of each element caused by molecular bonding. In ionic compounds, the oxidation numbers are the same as the element's ionic charge. Thus for KCl, potassium is assigned +1 and chlorine is assigned -1. [4] The complete set of rules for assigning oxidation numbers are discussed in the following sections.
An atom (or ion) whose oxidation number increases in a redox reaction is said to be oxidized (and is called a reducing agent). It is accomplished by loss of one or more electrons. The atom whose oxidation number decreases gains (receives) one or more electrons and is said to be reduced. This relation can be remembered by the following mnemonics.
When the metal has more than one possible ionic charge or oxidation number the name becomes ambiguous. In these cases the oxidation number (the same as the charge) of the metal ion is represented by a Roman numeral in parentheses immediately following the metal ion name. For example, in uranium(VI) fluoride the oxidation number of uranium is 6 ...
Group 10 elements are observed in oxidation states of +1 to +4. [2] The +2 oxidation state is common for nickel and palladium, while +2 and +4 are common for platinum. Oxidation states of -2 and -1 have also been observed for nickel [3] [4] and platinum, [5] and an oxidation state of +5 has been observed for palladium [6] and platinum. [7]
The maximum oxidation state in the first row transition metals is equal to the number of valence electrons from titanium (+4) up to manganese (+7), but decreases in the later elements. In the second row, the maximum occurs with ruthenium (+8), and in the third row, the maximum occurs with iridium (+9).
When an oxidizer (Ox) accepts a number z of electrons ( e −) to be converted in its reduced form (Red), the half-reaction is expressed as: Ox + z e − → Red The reaction quotient ( Q r ) is the ratio of the chemical activity ( a i ) of the reduced form (the reductant, a Red ) to the activity of the oxidized form (the oxidant, a ox ).