Rules
Stable nuclei of even Z more numerous than odd Z.
Stable nuclei of even N more numerous than odd N.
Stable nuclei of even A more numerous than odd A.
In general, stable nuclei of even A have even Z. Some exceptions exist, however, such as 2H, 6Li, 10B, and 14N
Only two stable structures are known for which Z is greater than N: 3He and 1H
Examining what happens to the N/Z ratio in a typical alpha decay: