Equipment such as mass spectrometers can measure the mass of atomic particles, while the elementary charge is typically known through calculations rather than direct measurement. The elementary charge is associated with protons and electrons, with atoms generally being neutral overall. When atoms gain or lose electrons, they can become positively or negatively charged. The discussion references Millikan's Oil Drop Experiment as a historical method for determining the charge of an electron. Understanding these concepts is essential for grasping atomic structure and behavior.