I chained 220 with a 7mm hook (I always, always use a hook two sizes up for a foundation chain when I'm making a scarf - it stops that annoying curve) and then, using a 6mm hook, simply worked half trebles (half doubles US) in the back loops.
Dans Minimalist Scarf-by HookedUp A perfect scarf for the minimalist man or woman in your life! Subtle vertical lines add understated interest to this easy and super-quick pattern. Instructions are included for customizing the length and the width. free pdf