By referring to specific examples from Act One of Hamlet, describe the atmosphere, mood, and tone of the play. I know Act One sets a dark,...

The most obvious part of Act I to refer to, when citing
examples that set atmosphere and mood, is scene i.  The scene begins on a bitterly cold
night, just after the clock has struck midnight (Barnardo:  "Tis now struck twelve.") --
a recognizable sort of  beginning for any ghost or horror story.  So, before a word is
spoken, there is, potentially, an established atmosphere of tension and
suspense.

We know that it is dark, because the characters
have trouble seeing each other.  This trouble seeing could also indicate that there is
fog or some other spooky condition.  When the first line of a play is, "Who's there?",
then it really sends a signal of tension and suspense to the audience.  These soldiers
are jumpy.  The question "Have you had quiet guard?" also indicates that there is some
underlying reason that these men are on edge.  This tense, suspenseful atmosphere
continues through scene i, culminating in the actual ghost story started by Barnardo
(lines 38 - 42) and the appearance of the ghost.

I would
have to say, however, that though scenes iv and v continue in the same spooky,
suspenseful, ghost story-esque vein of scene i, scenes ii and iii of this Act set
entirely different tones.

The court of scene ii is one of
regal calm, one in which the tones of pomp and circumstance, of order and control, are
contrasted against Hamlet's un-courtly behaviour.  The domestic tension established in
this scene, however, is very different in mood and tone from the ghostly atmosphere of
scene i.  And scene iii continues this domestic mood, lightening the atmosphere to the
jovial exchange of banter between Ophelia and Laertes.  This scene ends on a bit of a
tense note (when Polonius commands Ophelia to cut off contact with Hamlet), but the
overriding atmosphere and mood of the scene iii is light and
domestic.

Scenes iv and v concern Hamlet's confrontation
with the Ghost and hearken back to the mood created in scene
i.

This act begins with a very clear, very strong setting
of a particular mood and tone, but scenes ii and iii contrast this mood of suspense with
one of domestic and courtly order.  It is interesting to note that Hamlet, even before
he learns of the ghost's visitations, carries much more of the tone of darkness and
foreboding in his soliloquy of scene ii.  It's as if he is already connected internally
to the "rotten"-ness of Denmark, even though, on the surface, the court seems stable and
calm.