Its abundance is accounte
Its abundance is accounted for by a couple of reasons.  First, its phi and psi angles lie in the center of an allowed, minimum energy region of the Ramachandran map; and second, its radius allows for favorable Van der Waals interactions.  Theoretically it can be left-handed, but all of those found since their 1951 prediction by Pauling and Corey have been right-handed.  Each of its components occupies a vertical distance of 1.5 angstroms, with 3.6 of them per turn of its coils and a distance of .54 nanometers between those coils.  FTP, name this type of secondary structure in a protein, which bears a slight resemblance to the less common beta-pleated-sheet.
Its abundance is accounted for by a couple of reasons.  First, its phi and psi angles lie in the center of an allowed, minimum energy region of the Ramachandran map; and second, its radius allows for favorable Van der Waals interactions.  
alpha-helix