It is called the diction.
Angst, in writing, is like a dark story. One that has a sad, dark, etc. plot to it. On the other hand, tone is how a writer feel towards a topic.
The overlap lies in the fact that both essays present an opinion on an idea with the goal showing deep understanding and personal thoughts regarding an entity, with the difference lying in argumentative essays also showing the second side to something, whereas persuasive essays only show one.
