The chromatic scale is a sequence of semitones and includes every possible note within one octave. Here is the C chromatic scale:
The same scale could be written using flats. However, it is more common to do this when descending:
Because each chromatic scale contains every possible note within one octave, once you have learned one you have basically learned them all. As an example, the A chromatic scale contains exactly the same notes as the C chromatic scale, the only difference being the note upon which they start. This starting note, in all scales, is referred to as the root or key note.
A Chromatic scale: