chance vs happen

chance is a noun but happen is not a noun.

Word	Noun	Adjective	Verb	Adverb
chance	Yes	Yes	Yes	No
happen	No	No	Yes	No

As verbs, chance and happen are synonyms defined as:

Other synonyms of chance include bump, encounter, find.

As verbs, happen is a hypernym of chance; that is, happen is a word with a broader meaning than chance:

Other hypernyms of chance include come about, fall out, go on, hap, occur, pass, pass off, take place.

As verbs, happen is a hyponym of chance; that is, happen is a word with a more specific, narrower meaning than chance:

chance (noun)	happen (noun)
a risk involving danger
a measure of how likely it is that some event will occur; a number expressing the ratio of favorable cases to the whole number of cases possible
an unknown and unpredictable phenomenon that causes an event to result one way rather than another
a possibility due to a favorable combination of circumstances
the possibility of future success

chance (adjective)	happen (adjective)
occurring or appearing or singled out by chance

chance (verb)	happen (verb)
come upon, as if by accident; meet with	come to pass
take a risk in the hope of a favorable outcome	come into being; become reality
be the case by chance	happen, occur, or be the case in the course of events or by chance
	come upon, as if by accident; meet with
	chance to be or do something, without intention or causation