An argumentative follows when two groups disagree about something. An argumentative essay is also one that attempts/tries to change the readers mind, to convince the reader to agree with the point of the view of the writer. Argumentative essays attempt to be highly persuasive and logical.
An informative essay, however, is a form of writing that teaches/informs/instructs the reader about a topic. It should inform the reader of something new about a topic. Informative's are about facts, supporting details, or evidence.