chromatic is like the guitar (A, A#, B, C, C#, D, D#, E, F, F#, G, G#).....
modal is like a mountain dulcimer (D, E, F#, G, A, B, C#, D) some notes are missing, and on a fretted instrument the frets will be missing too
guitar neck = I I I I I II
mountain dulcimer neck = I I I I I I I
bad examples lol
http://www.dulcimers-plus.com/images...s/100_1171.jpg
http://www.kozmix.org/music/toys/pix/applecreek.jpg
those are mountain dulcimers, notice the goofy fret scale, that is modal