We define a process in which a species loses electrons an oxidation, and the corresponding gain of electrons is called a reduction (even though that seems somewhat counterintuitive). This transfer leads to the breakup of a Cl2 molecule into two Cl– ions. Here is the answer to where the electrons from the sodium atoms go, they are transferred to another reactant in the mixture, namely chlorine atoms. We have already looked at the structure of ionic compounds (in chapter 4) and have seen that they are best modeled (that is, represented and thought about) by considering NaCl as a three dimensional lattice of alternating positive (Na+) and negative (Cl–) ions. It turns out that this reaction is actually somewhat complicated (although we like it because it is explosive), so we will come back to it shortly.Īn easier reaction to analyze is that between sodium and chlorine to form sodium chloride. The overall reaction of sodium and water is: 2Na(s) + 2H wO(l) ↔ 2Na+(aq) + 2–OH(aq) + H 2(g) The “lost” electrons from sodium must go somewhere (since, in chemical reactions, we don’t need to consider matter-energy inter-conversion). In our example, sodium metal Na(s) reacts with water to form Na+(aq) – a completely different (and much less reactive) species. They lose electrons to another molecule and becomes positively charged. As the reaction proceeds (here we will use the sodium-water reaction as the focus of our discussion), the metal atoms becomes cations. Pure metals have no charge or permanent unequal distribution of charge (that makes them different, for example, from salts, like NaCl). Rusting is mechanistically similar to the reactions that occurs when copper turns green, silver tarnishes (turns black), and perhaps the favorite reaction of chemists everywhere, the explosive reaction that occurs when sodium metal is added to water.Īll of these reactions start off with a metal in its elemental form. The iron is transformed from a hard, non-polar metallic substance (Fe solid) into a powdery substance Fe 2O 3.nH 2O(s). You may have run into such reactions already (even if you did not know what they are called!) When iron is left in contact with oxygen (in air) and water, it rusts. In a redox reaction, polar products are generated from non-polar reactants. In contrast to acid-base reactions, there is distinct class of reaction, known as reduction-oxidation (or redox) reactions, that obey a different pattern.
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