Does scientific notation become negative when going forward or backward?

The scientific notation is negative if the number itself is negative and not otherwise.

Thus the scientific notation for -2500 is -2.5*103.

Perhaps what you were thinking was when the exponent, or power of 10, is negative. This is negative when the magnitude of the "ordinary" number is smaller than 1.

Thus 0.25 = 2.5*10-1

So, if the number itself is less than 0 and its magnitude is less than 1 (ie -1 < x < 0), then both are negative.

For example, -0.0025 = -2.5*10-3