Its all about Physics.

  Atomic Physics : Introduction: The branch of physics known as "atomic physics" focuses on the study of atoms as separate systems made up of electrons and atomic nuclei. Usually, the term "atomic physics" refers to the study of atomic structure and interatomic interactions.  The arrangement of electrons surrounding the nucleus and the mechanisms by which this arrangement changes are its main topics of interest. It is presumed that the term "atom" includes ions unless specifically specified that this consists of ions and neutral atoms.   Atomic Physics Due to the synonymy between the terms "atomic" and "nuclear" in common English, the word "atomic physics" can be linked to both nuclear energy and nuclear weapons. Atomic physics, which examines the atom as a system made up of a nucleus and electrons, is distinguished from nuclear physics, which examines nuclear reactions and unique characteristics of atomic nuclei.   In atomic ...