Neutron number

Nuclides that have the same mass number are called isobars.

[1] Chemical properties are primarily determined by proton number, which determines which chemical element the nuclide is a member of; neutron number has only a slight influence.

Neutron number is primarily of interest for nuclear properties.

Most odd neutron numbers have at most one stable nuclide (exceptions are 1 (2H and 3He), 5 (9Be and 10B), 7 (13C and 14N), 55 (97Mo and 99Ru) and 107 (179Hf and 180mTa)).

However, some even neutron numbers also have only one stable nuclide; these numbers are 0 (1H), 2 (4He), 4 (7Li), 84 (142Ce), 86 (146Nd) and 126 (208Pb), the case of 84 is special, since 142Ce is theoretically unstable to double beta decay, and the nuclides with 84 neutrons which are theoretically stable to both beta decay and double beta decay are 144Nd and 146Sm, but both nuclides are observed to alpha decay.