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58 PCB007 MAGAZINE I AUGUST 2018 The electromotive series is a list of metals whose order indicates the relative tendency to be oxidized, or to give up electrons. The elec- tromotive series begins with the metal most easily oxidized (i.e., the metal with the great- est electron-donating tendency) and ends with the metal least easily oxidized. The tendency to be oxidized is called the oxidation poten- tial and expressed in volts. The more negative the oxidation potential, the more readily oxida- tion takes place. The series is also called the re- placement series, since it indicates which met- als replace, or are replaced by, other metals. In general, a metal will replace any other metal lower in the series and will be replaced by any metal higher in the series. The tendency to be oxidized is not an ab- solute quantity; it can only be compared with the tendency of some other substance to be oxidized. In practice, it is measured relative to a standard hydrogen electrode, which is arbitrarily assigned an oxidation potential of zero. Table 1 shows select common metals and their oxidation potential, which is a mea - sure of their tendency to undergo the half re- action, in which some metal M loses n elec- trons e - , and acquires a positive charge of M +n , as in: M → M +n + n e - The driving force for the reaction is the dif- ference between the two half reactions (Equa- tion 1). The immersion gold reaction on nickel pro- ceeds at a much faster rate than on palladium. The immersion gold reaction on palladium proceeds at a lower rate and can only achieve limited gold thickness. Immersion gold thick- ness on palladium is in the order of 1.2–2.0 µin (0.03 – 0.05 µm). Table 1: Select metals and their oxidation potential. Equation 1.