At the same time, metal atoms of the electrode
have a tendency to go into the solution as ions and leave behind the
electrons at the electrode trying to make it negatively charged At
equilibrium, there is a separation of charges and depending on the
tendencies of the two opposing reactions, the electrode may be positively
or negatively charged with  respect to the solution A potential difference
develops between the electrode and the electrolyte which is called
electrode potential When the concentrations of all the species involved
in a half-cell is unity then the electrode potential is known as standard
electrode potential