wakefulness vs wakeful

wakefulness is a noun but wakeful is not a noun.

Word	Noun	Adjective	Verb	Adverb
wakefulness	Yes	No	No	No
wakeful	No	Yes	No	No

wakefulness (noun)	wakeful (noun)
a periodic state during which you are conscious and aware of the world
the process of paying close and continuous attention
a temporary state in which you are unable (or unwilling) to sleep

wakefulness (adjective)	wakeful (adjective)
	carefully observant or attentive; on the lookout for possible danger
	marked by full consciousness or alertness
	(of sleep) easily disturbed