The Collaborative International Dictionary of English v.0.48:

Unexpected \Un`ex*pect"ed\, a.
   Not expected; coming without warning; sudden. --
   Un`ex*pect"ed*ly, adv. -- Un`ex*pect"ed*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unexpectedness
    n 1: extraordinariness by virtue of being unexpected; "the
         unexpectedness of the warm welcome" [syn: unexpectedness,
         surprisingness] [ant: expectedness]

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "unexpectedness":
   abruptness, improbability, inexpectance, inexpectancy,
   inexpectation, no expectation, nonexpectation, precipitance,
   precipitancy, precipitateness, precipitatousness, suddenness,
   the unforeseen, the unlooked-for, unanticipation,
   unforeseeableness, unpredictability, unpredictableness,
   unpreparedness, unreadiness