Citizendia
Your Ad Here

In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny A chemical compound is a substance consisting of two or more different elements chemically bonded together in a fixed proportion by Mass. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. An ionic bond (or electrovalent bond) is a type of Chemical bond that can often form between Metal and Non-metal Ions (or Oxidation states are represented by Arabic numerals and can be positive, negative, or zero. The arabic numerals (often capitalized are the ten Digits (0 1 2 3 4 5 6 7 8 9 which—along with the system

The increase in oxidation state of an atom is known as an oxidation; a decrease in oxidation state is known as a reduction. Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state Such reactions involve the formal transfer of electrons, a net gain in electrons being a reduction and a net loss of electrons being an oxidation.

Here is the definition of the oxidation state listed by IUPAC:[1]

"Oxidation state :A measure of the degree of oxidation of an atom in a substance. The International Union of Pure and Applied Chemistry ( IUPAC) (aɪjuːpæk or ay-yoo-pec) is an international Non-governmental organization It is defined as the charge an atom might be imagined to have when electrons are counted according to an agreed-upon set of rules: (l) the oxidation state of a free element (uncombined element) is zero; (2) for a simple (monatomic) ion, the oxidation state is equal to the net charge on the ion; (3) hydrogen has an oxidation state of 1 and oxygen has an oxidation state of -2 when they are present in most compounds. (Exceptions to this are that hydrogen has an oxidation state of -1 in hydrides of active metals, e. g. LiH, and oxygen has an oxidation state of -1 in peroxides, e. g. H2O2; (4) 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. For example, the oxidation states of sulfur in H2S, S8 (elementary sulfur), SO2, SO3, and H2SO4 are, respectively: -2, 0, +4, +6 and +6. The higher the oxidation state of a given atom, the greater is its degree of oxidation; the lower the oxidation state, the greater is its degree of reduction. "

Contents

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. Lewis structures, also called Lewis-dot diagrams are diagrams that show the bonding between Atoms of a

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 ionization potential, ionization energy or EI of an Atom or Molecule is the Energy required to remove an Electron 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.

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 (that is smaller than the charge of the Electron)

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. Lewis structures, also called Lewis-dot diagrams are diagrams that show the bonding between Atoms of a In chemistry valence electrons are the Electrons contained in the outermost or valence, Electron shell of an Atom. 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. " Electronegativity " is the opposite of " Electropositivity," which describes an element's ability to donate electrons lone pair is a (valence electron pair without bonding or sharing with other Atoms They are found in the outermost Electron shell of an atom so lone pairs

For example, consider acetic acid:

The methyl group carbon atom has 6 valence electrons from its bonds to the hydrogen atoms because carbon is more electronegative than hydrogen. Acetic acid, also known as ethanoic acid, is an organic chemical compound, giving Vinegar its sour taste In Chemistry, a methyl group is a Hydrophobic Alkyl Functional group named after Methane (4 Also, 1 electron is gained from its bond with the other carbon atom because the electron pair in the C–C bond is split equally, giving a total of 7 electrons. A carbon-carbon bond is a Covalent bond between two Carbon Atoms. A neutral carbon atom would have 4 valence electrons, because carbon is in group 14 of the periodic table. History Carbon, Tin, and Lead, are a few of the elements well known in the ancient world - together with Sulfur, Iron, The difference, 4 – 7 = –3, is the oxidation state of that carbon atom. That is, if it is assumed that all the bonds were 100% ionic (which in fact they are not), the carbon would be described as C3-.

Following the same rules, the carboxylic acid carbon atom 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). Carboxylic acids are Organic acids characterized by the presence of a Carboxyl group, which has the formula -C(=OOH usually written -COOH or -CO2H 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.

Oxidation states can be useful for balancing chemical equations for redox reactions, because the changes in the oxidized atoms have to be balanced by the changes in the reduced atoms. For example, in the reaction of acetaldehyde with the Tollens' reagent to acetic acid (shown below), the carbonyl carbon atoms changes its oxidation state from +1 to +3 (oxidation). Acetaldehyde, sometimes known as ethanal, is an organic chemical compound with the formula C[[Hydrogen H]]3CH O or MeCHO Tollens' reagent is usually ammoniacal silver nitrate but can also be other compounds as long as there is an aqueous diamminesilver(I complex. This oxidation is balanced by reducing two equivalents of silver from Ag+ to Ago. Silver (ˈsɪlvɚ is a Chemical element with the symbol " Ag " (argentum from the Ancient Greek: ἀργήντος - argēntos gen

Change in oxidation state in Tollens reaction

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. In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by 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. Some typical rules that are used for assigning oxidation states of simple compounds follow:

Example: In 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. In Chemistry, hydroxide is the most common name for the diatomic Anion OH− consisting of Oxygen and Hydrogen As the compound is neutral, Cr has an oxidation state of +3.

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

Oxygen has 8 different oxidation states:

  1. -2 in most oxides. e. g. ZnO, CO2, H2O
  2. -1 in all peroxides.
  3. -1/2 as in superoxides. e. g. KO2
  4. -1/3 as in ozonides. e. g. RbO3
  5. 0 as in O2
  6. +1/2 as in dioxygenyl. e. g. O2+[AsF6]-
  7. +1 in O2F2
  8. +2 in OF2

Fractional oxidation states

The formal oxidation state of an atom in a Lewis structure is always an integer. However, fractional oxidation states are often used to represent the average oxidation states of several atoms in a structure. For example, in KO2, oxygen has an average oxidation state of −½, which results from having one oxygen atom with oxidation state 0 and one with oxidation state −1. In some cases, the atoms may indeed be equivalent due to resonance; in those cases, the structure cannot be represented by a single Lewis structure—several structures are required. Resonance in Chemistry is a theory used to represent and model certain types of non-classical Molecular structures Resonance is a key component

Oxidation number

Main article: Oxidation number

The terms oxidation state and oxidation number are often used interchangeably. The oxidation number of a central atom in a coordination compound is the charge that it would have if all the Ligands were removed along with the Electron pairs Rigorously, however, oxidation number is used in coordination chemistry with a slightly different meaning. The oxidation number of a central atom in a coordination compound is the charge that it would have if all the Ligands were removed along with the Electron pairs The term complex in Chemistry is usually used to describe molecules or ensembles formed by the combination of Ligands and metal Ions. In coordination chemistry, the rules used for counting electrons are different: every electron belongs to the ligand, regardless of electronegativity. Also, oxidation numbers are conventionally represented with Roman numerals while oxidation states use Arabic numerals.

History

The concept of oxidation state in its current meaning was introduced by W. M. Latimer in 1938. Wendell Mitchell Latimer (Born April 22, 1893 Died July 6, 1955) was a prominent Chemist notable Oxidation itself was first studied by Antoine Lavoisier who then held the belief that oxidation was literally the results of reactions of the elements with oxygen and that the common bond in any salt was based on oxygen. [2]

References

  1. ^ IUPAC Gold Book
  2. ^ The Origin of the Oxidation-State Concept William B. Jensen J. Chem. Educ. 2007, 84, 1418

See also

External links

A kibibyte (a contraction of ki lo bi nary byte) is a unit of Information or Computer storage, established by the International The International Union of Pure and Applied Chemistry ( IUPAC) (aɪjuːpæk or ay-yoo-pec) is an international Non-governmental organization Compendium of Chemical Terminology (ISBN 0-86542-684-8 is a book published by IUPAC containing internationally accepted definitions for terms in Chemistry.

Dictionary

oxidation state

-noun

  1. (chemistry) the state of an atom having a particular oxidation number
© 2009 citizendia.org; parts available under the terms of GNU Free Documentation License, from http://en.wikipedia.org
 Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic