  A thick neutron skin emerges from the first determination of root mean square
radii of the proton distributions for $^{17-22}$N from charge changing cross
section measurements around 900$A$ MeV at GSI. Neutron halo effects are
signaled for $^{22}$N from an increase in the proton and matter radii. The
radii suggest an unconventional shell gap at $N$ = 14 arising from the
attractive proton-neutron tensor interaction, in good agreement with shell
model calculations. $Ab$ $initio$, in-medium similarity re-normalization group,
calculations with a state-of-the-art chiral nucleon-nucleon and three-nucleon
interaction reproduce well the data approaching the neutron drip-line isotopes
but are challenged in explaining the complete isotopic trend of the radii.
