The standard model accounts for forces. Nuclei have structures beyond the particle level. Several models describe the collection of protons and neutrons that form a nucleus. The liquid drop model [local] is one. {Liquid drop illustration. [local]} The nuclear shell model [local] (starting with an intermediate slide) is another. Alternative source for nuclear shell model [local]

Nuclei are not always spherical. See figures [local] about nuclear shapes.

Access table of contents of a very thorough Web discussion.