Use of sharps and flats when writing altered notes to chords in key

1. Why are sharps and flats used?
2. Can you use sharps in a flat key?
3. What are sharp and flat chords?

Why are sharps and flats used?

Sharps indicate a raised note and the direction it wants to resolve. Flats indicate a lowered note and the direction it wants to resolve. Accidentals when written correctly, make lines easier to read.

Can you use sharps in a flat key?

There is also the Whole Tone scale that can have sharps and flats. There is no rule that excludes them from being in the same scale.

What are sharp and flat chords?

What are sharps and flats? ... They appear as suffixes to natural notes: A sharp is one semitone higher in pitch, while a flat is one semitone lower. So, for instance, a C♯ is one semitone higher (or one fret up) than a C, and a D♭ is one semitone lower (or one fret down) than a D.