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Unit 11: The Metallic World—Electrochemistry and Coordination Compounds

Section 1: Introduction

We're out running an errand when the phone rings. One of our friends has an extra ticket to this weekend's game, and would love to take us. After we get off the phone, we realize that the battery is running low, so we make sure to plug it into the charger when we return home. The weather is nice, so we take a laptop outside to work on the paper due on Monday.

Batteries, especially rechargeable ones, have made communication much more efficient and computing more portable in the past two decades. Improvement in battery technology has allowed for a scaling down of sizes, with more power and longer life in progressively smaller packaging. Every portable electronic device, whether we realize it or not, is fueled by chemistry—specifically, the chemistry of oxidation and reduction, or redox. (Figure 11-1)

Rechargeable Batteries

Figure 11-1. Rechargeable Batteries

© Wikimedia Commons, Public Domain. Author: Mmckinley, 21 January 2009.

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Rechargeable Batteries

Figure 11-1. Rechargeable Batteries

Many personal electronics use a rechargeable battery system for power. The batteries run on oxidation-reduction, or redox, chemistry.

In Unit 4, we learned about oxidation states, and in Unit 10 we saw simple examples of reactions in which those oxidation states change. When the oxidation states or reactants change, one species loses electrons (referred to as "oxidation" of the species) and another gains the electrons (referred to as "reduction"). When a redox reaction can be set up so that the electrons are forced to move through a wire, it is producing electricity, or electrical current. This makes electrochemistry (the name given to various applications of redox reactions) an incredibly useful branch of chemistry.

We may also recall from Unit 9 that not all reactions proceed without outside intervention. Application of an electric current can force redox reactions to run "backwards," that is, in the nonspontaneous direction. This, too, can be used to great advantage. For example, recharging a phone forces a redox reaction backwards, so that it can go right back to running in the forward direction and allow us to take that call from our friend. In this unit, we will take a closer look at how redox processes work, in both directions.

We also will examine transition metal chemistry. Many redox reactions involve transition metals, and the presence of these metals is often the reason for special disposal instructions for electronic equipment. Metals can do plenty of interesting things besides redox though. Many of them can produce intensely colored compounds, a phenomenon which is significantly less common in compounds made entirely of nonmetals. Several metals also play critical roles in physiological processes, even when they are present only in trace amounts. We will see a few of these examples in the final sections of this unit.

Glossary

Oxidation

Loss of electrons by one species over the course of a chemical reaction.

Redox

The shorthand term for a "reduction-oxidation" reaction.

Reduction

A reaction in which an atom, molecule, or ion gains electrons. Reduction is always accompanied by a separate oxidation process, a reaction in which another reactant loses the electrons.

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