isolated system (plural isolated systems) (physics) A system that does not interact with its surroundings. Depending on context this may mean that its total energy and/or momentum stay constant.
Explanation:
An isolated system is a thermodynamic system that cannot exchange either energy or matter outside the boundaries of the system. ... The system may be enclosed such that neither energy nor mass may enter or exit.
The location of the electrons in the Thomson's plum pudding model of the atom are contained in orbitals. These orbitals are what make the element stable or unstable