text: The values of the neutron drip line are only known for the first ten elements, hydrogen to neon. For oxygen (Z = 8), the maximal number of bound neutrons is 16, rendering O the heaviest particle-bound oxygen isotope. For neon (Z = 10), the maximal number of bound neutrons increases to 24 in the heaviest particle-stable isotope Ne. The location of the neutron drip line for fluorine and neon was determined in 2017 by the non-observation of isotopes immediately beyond the drip line. The same experiment found that the heaviest bound isotope of the next element, sodium, is at least Na. These were the first new discoveries along the neutron drip line in over twenty years.
  The neutron drip line is expected to diverge from the line of beta stability after calcium with an average neutron-to-proton ratio of 2.4. Hence, is predicted that the neutron drip line will fall out of reach for elements beyond zinc (where the drip line is estimated around N = 60) or possibly zirconium (estimated N = 88), as no known experimental techniques are theoretically capable of creating the necessary imbalance of protons and neutrons in drip line isotopes of heavier elements. Indeed, neutron-rich isotopes such as S, Cl, and Ar that were calculated to lie beyond the drip line have been reported as bound in 2017–2019, indicating that the neutron drip line may lie even farther away from the beta-stability line than predicted.
  The table below lists the heaviest particle-bound isotope of the first ten elements.
  Not all lighter isotopes are bound. For example, Na is bound, but Na is unbound. As another example, although He and He are bound, He and He are not.