One difference in Antigone's tone is that it is suddenly full of self-pity whereas before her tone was full of pure righteousness.
In this speech, she is begging the chorus to empathize with her due to all that she has suffered. She certainly has suffered a great deal in that she has lost both her incestuous father and mother to death and now both of her brothers as well. Not only that, she feels she is being punished for the incestuous sins of her father and mother.
Prior to this speech, she compares her death to the death of the goddess Niobe, daughter of Tantalus, who died "on top of mountain" as "she slowly turned to stone" (830-833, Translated by David Feldshuh). But the chorus points out that Niobe was a goddess while Antigone is a mortal and should therefore not be comparing herself to a goddess. It is at this point that Antigone believes she is being laughed at by the chorus, as we see in her line, "Oh! I am mocked!" (845). After this, a debate begins between Antigone and the chorus about whether or not Antigone has acted rashly. This finally leads to Antigone's speech about the incest of her parents and how Antigone is being punished for their sins. Since she sees that the chorus is mocking her, she now sees that she is dying without pity, as we see in the final lines of her speech:
My brother, also cursed,
His death destroyed my life.
No pity for my pain.
I join the house of Oedipus in the dark. (874-876, Translated by David Feldshuh)
Therefore, we see through Antigone's lines that her tone has changed because she is full of self-pity since now she sees that the chorus believes she was wrong.