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Encyclopedia > Oxidation state

In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are represented by Arabic numerals and can be positive, negative, or zero. Thus, H+ would have an oxidation state of 1+. For other uses, see Chemistry (disambiguation). ... The most fundamental reactions in chemistry are the redox processes. ... “Atomic” redirects here. ... A chemical compound is a chemical substance consisting of two or more different chemically bonded chemical elements, with a fixed ratio determining the composition. ... Electric charge is a fundamental property of some subatomic particles, which determines their electromagnetic interactions. ...


The increase in oxidation state of an atom is known as an oxidation: a decrease in oxidation state is known as a reduction. Such reactions involve the transfer of electrons, a net gain in electrons being a reduction and a net loss of electrons being an oxidation. Semi-accurate illustration of a redox reaction Redox reactions include all chemical processes in which atoms have their oxidation number (oxidation state) changed. ...

Contents

Formal vs. spectroscopic oxidation states

Although formal oxidation states can be helpful for classifying compounds, they are unmeasureable and their physical meaning can be ambiguous. Formal oxidation states require particular caution for molecules where the bonding is covalent, since the formal oxidation states require the heterolytic removal of ligands, which essentially denies covalency. Spectroscopic oxidation states, as defined by Jorgenson and reiterated by Wieghart, are measureables that are bench-marked using spectroscopic and crystallographic data.[1] Like many concepts in chemistry, spectroscopic oxidation states is powerful but requires collateral measurements. Formal oxidation states, on the other hand, result from arithmetic rules, not bonding. Skill in assigning formal oxidation states is considered essential, especially in inorganic chemistry. In chemistry, heterolysis (from Greek ἑτερος, heteros, different, and λυσις, lusis, loosening) is chemical bond cleavage of a neutral molecule generating a cation and an anion. ... Covalent bonding is a description of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. ...


Calculation of formal oxidation states

There are two common ways of computing the oxidation state of an atom in a compound. The first one is used for molecules when one has a Lewis structure, as is often the case for organic molecules, while the second one is used for simple compounds (molecular or not) and does not require a Lewis structure. G. N. Lewis Lewis structures, also called electron-dot structures or electron-dot diagrams, are diagrams that show the bonding between atoms of a molecule, and the lone pairs of electrons that may exist in the molecule. ...


It should be remembered that the oxidation state of an atom does not represent the "real" charge on that atom: this is particularly true of high oxidation states, where the ionization energy required to produce a multiply positive ion are far greater than the energies available in chemical reactions. The assignment of electrons between atoms in calculating an oxidation state is purely a formalism, albeit a useful one for the understanding of many chemical reactions. The ionization energy (IE) of an atom or of a molecule is the energy required to strip it of an electron. ...


For more about issues with calculating atomic charges, see partial charge. A partial charge is a charge with an absolute value of less than one elementary charge unit. ...


From a Lewis structure

When a Lewis structure of a molecule is available, the oxidation states may be assigned unambiguously by computing the difference between the number of valence electrons that a neutral atom of that element would have and the number of electrons that "belong" to it in the Lewis structure. For purposes of computing oxidation states, electrons in a bond between atoms of different elements belong to the most electronegative atom; electrons in a bond between atoms of the same element are split equally, and electrons in lone pair belong only to the atom with the lone pair. G. N. Lewis Lewis structures, also called electron-dot structures or electron-dot diagrams, are diagrams that show the bonding between atoms of a molecule, and the lone pairs of electrons that may exist in the molecule. ...


For example, consider acetic acid:


Image File history File links Acetic_acid_structures4. ...


The carbon atom on the left has 6 valence electrons from its bonds to the hydrogen atoms, because carbon is more electronegative than hydrogen, and 1 electron from its bond with the other carbon atom, because the electron pair in the C–C bond is split equally, for a total of 7 electrons. A neutral carbon atom would have 4 valence electrons, because carbon is in group 14 of the periodic table. The difference, 4 – 7 = –3, is the oxidation state of that carbon atom. That is, if all the bonds were 100% ionic (which they clearly are not!), the carbon would described as C3-.


Following the same rules, the carbon on the right has an oxidation state of +3 (it only gets one valence electron from the C–C bond; the oxygen atoms get all the other electrons because oxygen is more electronegative than carbon). The oxygen atoms both have an oxidation state of –2; they get 8 electrons each (4 from the lone pairs and 4 from the bonds), while a neutral oxygen atom would have 6. The hydrogen atoms all have oxidation state +1, because they surrender their electron to the more electronegative atoms to which they are bonded.


Without a Lewis structure

The algebraic sum of oxidation states of all atoms in a neutral molecule must be zero, while in ions the algebraic sum of the oxidation states of the constituent atoms must be equal to the charge on the ion. This fact, combined with the fact that some elements almost always have certain oxidation states, allows one to compute the oxidation states for atoms in simple compounds. In chemistry, a molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds [1] [2] [3] [4] [5]. Chemical substances are not infinitely divisible into smaller fractions of the same substance: a molecule is generally considered the smallest particle of a pure...


Other rules and guidelines

This article is about the chemistry of hydrogen. ... The most fundamental reactions in chemistry are the redox processes. ... General Name, Symbol, Number sodium, Na, 11 Chemical series alkali metals Group, Period, Block 1, 3, s Appearance silvery white Atomic mass 22. ... General Name, Symbol, Number aluminium, Al, 13 Chemical series poor metals Group, Period, Block 13, 3, p Appearance silvery Atomic mass 26. ... General Name, Symbol, Number boron, B, 5 Chemical series metalloids Group, Period, Block 13, 2, p Appearance black/brown Atomic mass 10. ... Sodium hydride is a highly flammable, and corrosive chemical compound with formula NaH and CAS number 7646-69-7. ... Sodium borohydride, also known as sodium tetrahydroborate, has the chemical formula NaBH4. ... Lithium aluminium hydride (LiAlH4), commonly abbreviated to LAH, is a powerful reducing agent used in organic chemistry. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ... Peroxide has three distinct meanings: // Main article: hydrogen peroxide In common usage, peroxide is an aqueous solution of hydrogen peroxide (HOOH or H2O2) sold for use as a disinfectant or mild bleach. ... Lewis electron configuration of superoxide. ... Oxygen difluoride is a chemical compound whose formula is OF2. ... The alkali metals are the series of elements in Group 1 (IUPAC style) of the periodic table (excluding hydrogen in all but one rare circumstance): lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). ... Alkalides are chemical compounds in which alkali metals are anions (that is, they bear a negative charge). ... The alkaline earth metals are the series of elements in Group 2 (IUPAC style) of the periodic table: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra) (not always considered due to its radioactivity and very short half-life). ... The halogens are a chemical series of nonmetals. ...

Example

With the example, Cr(OH)3, oxygen has an oxidation state of −2 (no fluorine, O-O bonds present), and hydrogen has a state of +1 (bonded to oxygen). So, the triple hydroxide group has a charge of 3 × (−2 + 1) = −3. As the compound is neutral, Cr has an oxidation state of +3. Hydroxide is a polyatomic ion consisting of oxygen and hydrogen: OH− It has a charge of −1. ...


Elements with multiple oxidation states

Most elements have more than one possible oxidation state — with carbon having nine, as follows below:

  1. –4: CH4
  2. –3: C2H6
  3. –2: CH3F
  4. –1: C2H2
  5.  0: CH2F2
  6. +1: C2H2F4
  7. +2: CHF3
  8. +3: C2F6
  9. +4: CF4

For an exhaustive list of the possible oxidation states of each element, see the Standard Periodic Table. The periodic table of the chemical elements is a tabular method of displaying the chemical elements, first devised in 1869 by the Russian chemist Dmitri Mendeleev. ...


References

  1. ^ Bill, E.; Bothe, E.; Chaudhuri, P.; Chlopek, K.; Herebian, D.; Kokatam, S.; Ray, K.; Weyhermueller, T.; Neese, F.; Wieghardt, K., "Molecular and electronic structure of four- and five-coordinate cobalt complexes containing two o-phenylenediamine- or two o-aminophenol-type ligands at various oxidation levels: An experimental, density functional, and correlated ab initio study", Chemistry--A European Journal, 2005, 11, 204-224.

See also

English chemists John Daniell (left) and Michael Faraday (right), both credited to be founders of electrochemistry as known today. ... The oxidation number of an element in a molecule or complex is the charge that it would have if all the ligands were removed along with the electron pairs that were shared with the central atom[1]. It is used in the inorganic nomenclature of inorganic compounds. ... In chemistry, valence, also known as valency or valency number, is a measure of the number of chemical bonds formed by the atoms of a given element. ...

External links

  • "Oxidation state"PDF from the IUPAC Gold Book
  • "High Oxidation States of 5d Transition Metals"

  Results from FactBites:
 
Oxidation state - Wikipedia, the free encyclopedia (530 words)
In chemistry, the oxidation state is a measure of the degree of oxidation of an atom in a chemical compound.
The increase in oxidation state of an atom is known as an oxidation: a decrease in oxidation state is known as a reduction.
It should be remembered that the oxidation state of an atom does not necessarily represent the real charge on that atom: this is particularly true of high oxidation states, where the ionization energy required to produce a multiply positive ion are far greater than the energies available in chemical reactions.
Redox - Wikipedia, the free encyclopedia (937 words)
This can be a simple redox process, such as the oxidation of carbon to yield carbon dioxide, it could be the reduction of carbon by hydrogen to yield methane, or it could be the oxidation of sugar in the human body, through a series of very complex electron transfer processes.
Formerly, oxidation simply meant the addition of oxygen or the removing of hydrogen (hence the name oxidation), and reduction was removal of oxygen or the addition of hydrogen.
The redox state is reflected in the balance of several sets of metabolites (e.g., lactate and pyruvate, beta-hydroxybutyrate and acetoacetate) whose interconversion is dependent on these ratios.
  More results at FactBites »

 
 

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