Oxidation occurs when the oxidation number of an atom becomes larger.
The argument (going on inside your head) would go like this if you wanted to know, for example, what an oxidising agent did in terms of electrons: An oxidising agent oxidises something else.MnO, for example, is ionic enough to be considered a salt that contains Mn2 and O2- ions.Metathesis reactions include acid-base reactions that involve the transfer of an H ion from a Brnsted acid to a Brnsted base.Jim Clark 2002 (updated January 2013).Understanding is a lot safer than thoughtless learning!An update on oxidising and reducing agents.Questions on redox definitions answers, where would you like to go now?That means that an oxidising agent takes electrons from that other substance.There is no change in the oxidation number of any atom in either of the metathesis reactions, for example.The metals in Group IA form compounds (such as Li3N and Na2S) in which the metal atom is in the 1 oxidation state.The fact that an active metal such as sodium is a strong reducing agent should tell us something about the relative strength of the Na ion as an oxidizing agent.
2 Fe( s ) O2( g ) 2 FeO( s ) 2 Fe( s ) 3 O2( g ) 2 Fe2O3( s ) Molten iron even reacts with water to form an aqueous solution of Fe2 ions and H2 gas.
What changes in this reaction is the oxidation state of these atoms.
Reduction is gain of electrons (OIL RIG).
Personally, I would recommend that you work it out if you need.
This problem becomes even more severe when we turn to the chemistry of the transition metals.
In other words, if aluminum reduces Fe2O3 to form Al2O3 and iron metal, aluminum must be a stronger reducing agent than iron.This is easily the most important use of the terms oxidation and reduction at A' level.Consider the relative strength of iron and aluminum, for example.There is some covalent character in even the most ionic compounds and vice versa.Chemists therefore developed a model for these reactions that focused on the transfer of electrons.(a) Hg22( aq ) 2 OH-( aq ) Hg2O( s ) H2O( l ) (b) Hg22( aq ) Sn2( aq ) 2 Hg( l ) Sn4( aq ) (c) Hg22( aq ) H2S( aq ) Hg( l ) HgS( s ) 2 H( aq ).An important feature of oxidation-reduction reactions can be recognized by examining what happens to the copper in this pair of reactions.The concept of oxidation number is nothing more than a bookkeeping system used to keep track of electrons in chemical reactions.Magnesium metal, for example, was thought to lose electrons to form Mg2 ions when it reacted with oxygen.
Oxidation Numbers Versus the True Charge on Ions The terms ionic and covalent describe the extremes of a continuum of bonding.
Questions to keep in mind while assigning oxidation numbers include the following: Are there any recognizable ions hidden in the molecule?
If you rewrite this as an ionic equation, it turns out that the oxide ions are spectator ions and you are left with: A last comment on oxidising and reducing agents.