careless vs carelessness

careless is not a noun while carelessness is a noun.

Word	Noun	Adjective	Verb	Adverb
careless	No	Yes	No	No
carelessness	Yes	No	No	No

careless (noun)	carelessness (noun)
	failure to act with the prudence that a reasonable person would exercise under the same circumstances
	the quality of not being careful or taking pains

careless (adjective)	carelessness (adjective)
marked by lack of attention or consideration or forethought or thoroughness; not careful
effortless and unstudied
(usually followed by `of') without due thought or consideration