word looked up :

Oxidation number : Oxidation state

The oxidation state or oxidation number is defined as the sum of negative and positive charges in an atom, which indirectly indicates the number of electrons it has accepted or donated. The oxidation number is a convenient conceptual approximation when working with complex electrochemical reactions that eases the tracking of electrons and helps verify that they have been conserved. This is especially useful whilst expressing complex half-reaction equations involved in oxidation/reduction reactions.

Atoms are defined as having an oxidation number of zero, meaning that they are electrically neutral. The positive protons in the nucleus balance the negative electron cloud surrounding it, there being equal numbers of both. If an atom donates an electron it has more protons than electrons and becomes positive. This ion is said to have an oxidation number of +1. Conversely if an atom accepts an electron it becomes negatively charged, gaining an oxidation number of -1. In summary, if an atom or ion donates an electron in a reaction its oxidation state is increased by one, if an element accepts an electron its oxidation state is decreased by one.

Oxidation numbers are denoted in chemical names by bracketed roman numerals placed immediately after the relevant element. For example, an iron ion, with an oxidation state of +3 is expressed as iron (III). Manganese with an oxidation state of +7 present in manganese oxide is given the name manganese (VII) oxide. The motive for placing oxidation numbers in names is only to distinguish between different compounds of the same elements. The actual charge (positive/negative) of the ion isn't expressed because it isn't necessary for this purpose.

In chemical formulae, the oxidation number of ions is placed in superscript after the element's symbol. For example, oxygen (II) is written as O^2-. Oxidation numbers of neutral numbers are not expressed. The following formula describes the element I₂ accepting two electrons to gain an oxidation number of -1.

 I₂ + 2e^- -> 2I^-

When dealing with reactions, the following rules define oxidation number:

The atom with the greater Electronegativity of disimiliar atoms sharing an electron is counted as receiving the electron.
Identical atoms sharing an electron are each credited with one/half of the electron.

Sometimes it isn't immediately obvious what the oxidation number of ions in a molecule are from its molecular formula. For example, given Cr(OH)₃, no oxidation numbers are present yet it is clear that ionic bonding is occurring.

There are a number of rules that can be used in determining an ions atomic number:

The oxidation number of (neutral) atoms equal zero.
In neutral molecules, the sum of the oxidation numbers adds up to zero.
Fluorine always has a -1 oxidation number within compounds.
Oxygen has an oxidation number of -2 in compounds, except (i) in the presence of fluorine, in which fluorine's oxidation number takes precedence; (ii) in oxygen-oxygen bonds, where one oxygen must neutralize the other's charge; (iii) in peroxide compounds, in which it takes an oxidation number of -1.
Group I ions have an oxidation number equal to +1 within compounds.
Group II ions have an oxidation number of +2 within compounds.
Halogens, besides fluorine, generally have -1 oxidation numbers in compounds. This rule can be broken in the presence of oxygen or other halogens, where the oxidation numbers can be positive.
Hydrogen always has an oxidation number of +1 oxidation number in compounds, except in metal hydrides.

With the example, Cr(OH)₃, oxygen has an oxidation number of -2 (no fluorine, O-O bonds or peroxide present), and hydrogen has a state of +1 (not a metal hydride). So, the triple hydroxide group has a charge of 3*(-2 + 1) = -3. As the compound is neutral, Cr has to have a charge of +3.

See also: Electrochemistry, valency

Anthony, in the Mississippi citizens of Niagara Falls resolved to satisfy this requirement by Falls. They perceived that a better site could nowhere be found on scenery, Niagara is a kind of half-way house between the East and Tonawanda it commands the great waterway of the Lakes and the St. States and Canada are focussed there, and cross the river.html">river.html">river by the Central and Hudson River, the Lehigh Valley, the Buffalo, Trunk of Canada, are some of these lines. Draining as it does the square.html">square miles, with an aggregate basin of 290,000 square miles, the every second is something like 300,000 cubic feet; and this, with whirlpool rapids below, is equivalent to about nine million, or, power. Moreover, the great lakes discharging--into each other form little affected by flood.html">flood or drought, the supply of pure water.html">water is that a rainfall of three.html">three inches in twenty-four hours over the Huron, which, with Lake Michigan, would take as long to overflow full effect of the flood was expended at the Falls. The first outcome of the movement was the Niagara River Hydraulic the Niagara Falls Power Company. The old plan of utilising the and the company adopted that of the late Mr. Thomas Evershed, it consists in tapping the river above the Falls, and using the restoring the water to the river below the Falls; but instead of a conduit. To this end some fifteen hundred acres of spare land, at the low price of three hundred dollars an acre.html">acre; and we believe a yearly rental of two hundred dollars an acre can even now be.

On wordlookup.net

All is still licensed under the GNU FDL.
It uses material from the wikipedia.

navig stuff