Electrode potential is concentration dependent as it is composed of two half-cells with same electrodes but different concentrations. One acting to dilute a more concentrated solution, while the other concentrates a more diluted solution — which then creates a voltage that is in equilibrium. This why we need both positive and negative sides of a battery as a power source and make something work.
Ionic compounds form when metals transfer valence electrons to nonmetals. Ionic compounds exist as crystals rather than molecules. A crystal consists of many alternating positive and negative ions bonded together in a matrix.