Watch the Big Pile O' Sassy online guitar lesson by Fareed Haque from 30 Beginner Jazz Licks You MUST Know
The chromatic movement here is a big part of the slick sound of this lick. The chromatic notes surround the 6th (of Abmaj7) chromatic from above and then by step from below. Notice that the ending of these licks always has a rhythmic element as well as a melodic one. We add the Bb on the end because it swings to end off of the one: F to Bb played on beats "1 &". Sing it and you'll see why they call it "bebop" - the notes end off the beat just like the rhythm in the phrase bebop; "1 &” sounds like "bebop"!
See Fareed's Tip #1 in the PDF