The directors of any corporation organized under this chapter may, by the articles of incorporation or any amendment thereto, or by a vote of the stockholders, be divided into two or three classes: the term of office of those of the first class to expire at the annual meeting next ensuing; of the second class one year thereafter; of the third class two years thereafter, and at each annual election held after such classification and election, directors shall be chosen for a full term, as the case may be, to succeed those whose terms expire.