Electron flow and conventional current
Electrons travel through the wire from the negative terminal to the positive one. But by the convention of physics, the current is marked the other way.
Figure to be added
Electron flow
From the negative terminal (anode) to the positive terminal (cathode) through the wire.
What actually moves.
Conventional current
From the positive terminal (cathode) to the negative terminal (anode).
The direction agreed before electrons were discovered, still used in circuit diagrams.
Naming the electrodes of any cell
To tell the anode from the cathode in a given electrochemical cell, these three points help:
The activity series
The metal higher in the activity series acts as the anode; the lower one as the cathode.
The reactions
Oxidation happens at the anode; reduction at the cathode.
The terminals
The anode is the negative terminal of the cell; the cathode the positive.
Both flows are true at once
The two arrows in figure 12.1.5 are not two different currents. They describe the same flow: electrons one way is the same as positive current the other way. Questions usually ask about the conventional current.
Why the rules agree
The three points are one idea seen from three sides. The more active metal gives up electrons more readily (the activity series), so it is the one oxidised (the reaction), and the electrons it leaves behind make it negative (the terminal). Know any one of the three and you can work out the other two. In a zinc-copper cell, for example, zinc is higher in the series, so zinc is oxidised, is the anode and is the negative terminal, and electrons leave it through the wire.
Electrons out of the anode, current into it
Electrons flow through the wire from anode (−) to cathode (+); conventional current is marked from cathode (+) to anode (−).