Copper is more reactive than silver. Metal reactivity is defined by an atom’s tendency to lose electrons (oxidation) and form a positive ion. Copper atoms have a greater drive to lose electrons and become copper ions ($ \text{Cu}^{2+}\() compared to silver atoms becoming silver ions (\) \text{Ag}^{+}\(). This difference places copper higher on the scale of metal reactivity.
Defining Metal Reactivity
Chemists use the Activity Series (or Reactivity Series) to organize and predict the behavior of metallic elements. This ordered list ranks metals according to their tendency to undergo oxidation. Metals higher on the list are more reactive because they lose electrons more easily than those below them. The Activity Series allows prediction of spontaneous reactions, such as a more reactive metal displacing the ions of a less reactive metal from a solution. Copper is located above silver, indicating that copper metal is more readily oxidized.
Quantifying the Difference
The precise, quantitative measure of a metal’s reactivity is the Standard Reduction Potential (\)E^\circ$), measured in volts. This value indicates the tendency of an ion to gain electrons, which is the opposite of reactivity. A less positive \(E^\circ\) value signifies a greater tendency for the neutral metal atom to lose electrons, indicating higher reactivity. The half-reaction for silver ions (\(\text{Ag}^+ + e^- \rightarrow \text{Ag}\)) has an \(E^\circ\) of approximately \(+0.80\) Volts. In contrast, the half-reaction for copper ions (\(\text{Cu}^{2+} + 2e^- \rightarrow \text{Cu}\)) has a less positive \(E^\circ\) value of about \(+0.34\) Volts. Since copper’s \(E^\circ\) is significantly less positive than silver’s, it confirms that copper metal has a greater tendency to be oxidized.
Real-World Manifestations of Reactivity
The difference in reactivity is demonstrated through displacement reactions. If solid copper metal is placed into a solution containing silver ions, the copper spontaneously reacts, dissolving to form copper ions while depositing solid silver metal. This displacement confirms copper’s greater tendency to lose electrons. Silver’s lower reactivity makes it suitable for applications like electrical contacts and fine jewelry, as it resists oxidation and corrosion better than copper. Copper, being more reactive, readily reacts with atmospheric oxygen, water, and carbon dioxide to form a protective greenish-blue layer of copper carbonate, known as patina.