Atomic radius across periods

The radii of periods 2 and 3 are listed in picometres. You will find the change at each step, test that a period really shrinks, and measure the jump from fluorine to sodium. Then the program draws the radii.

The idea. Across a period the radius falls at every step. At the start of a new period it jumps up, because a shell is added.

Your tasks.

1. In steps, return the list of changes from each radius to the next.
2. In shrinks, return True if every step is negative.
3. Find jump, the rise in radius from fluorine to sodium, in pm.