The chromatic scale ascends and descends entirely by semitone steps from a root to its octave. As a general rule and the diagram below shows, sharps are used when ascending and flats are used when descending. When a chromatic statement (full or part scale) is introduced to a key with sharps or flats, the natural sign is used to sharpen a flat note and flatten a sharp note. Enharmonic tones such as C# & Dflat are notes of the same pitch that are specific to the keys they so relate eg. The Bflat is proper to the key of F (Dm) where the A# is not. The chromatic scale contains the tones of all scales that can be constructed from the chromatic note range of all 12 tones in the universally accepted system of Equal Temperament.
Chromatic Scale - C C# D D# E F F# G G# A A# B C
C D- D E- E F G- G A- A B- B C