understanding mos is like the task of knowing where each employee is in a large home improvement store (without looking inside the store). an analyst knows the number of employees working at the store and each employee's department. he also knows that employees do not step on each other toes and employees stand in the aisle rather than on the merchandise shelves. employees leave their own department to help customers locate merchandise in other departments or to check inventory. an analyst giving the location of all employees in the store at a selected moment without looking inside is like a chemist calculating the mos of a molecule. just as mos cannot tell the exact location of each electron, the exact location of each employee is not known. an mo having a nodal plane is like the conclusion that employees walk down aisles and not through shelves. although electrons are contributed from a specific atom, the electron fills an mo without regard to its source atom. this is like an employee leaving his department to walk elsewhere in the store during the day. so, an mo is an incomplete description of an electron just as the analyst's calculations about the unseen store is an incomplete guess about employee locations.