Ranking the atoms of period 3 by size

The radii of the period 3 atoms are stored in a dictionary. You will find the largest atom, list the elements from the smallest to the largest, and work out how much the radius falls across the period.

The idea. Across a period the radius falls, so the order by size is the reverse of the order in the period.

Your tasks.

1. Set largest to the element with the largest radius.
2. Set order to the list of elements from the smallest atom to the largest.
3. Set fall to the fall in radius, in pm, from sodium to chlorine.