I've been listening songs and anime dialogues that end sentences with ～もの or even cuter version ～もん for so long that I am able to see how the word denotes reasons or excuses like:
おなか空いたもん (when the character was asked why she finished the cake all by herself)
I have no problem with the grammatical structure of the sentences that end with ～もの when the words before もの are verbs or adjectives, but I am confused when the words that precede the もの are nouns, they need to put the copula だ or です before the もの, for example:
Shouldn't it be の or な particles between the nouns and もの? How does that work, in term of grammar? Or is this usage of もの simply colloquial or slangy that does not have to follow any grammar rule?