In the 5th century BCE Empedocles conceptualized Nature as comprising atomic elements. A century later Aristotle elaborated that these elements comprised a physical substrate which emerged from ethereal “forms” – an idea originally espoused by Plato, Aristotle’s teacher. Forms comprised the essences which begat Nature: the exhibition of existence. Forms took form as elements.
Atoms were considered the most minuscule particle of matter until 1897, when English physicist J.J. Thomson found something smaller, which he called corpuscles. What Thomson discovered was the subatomic particle now called the electron.
Experimenting with cathode ray emissions, Thomson concluded that atoms were divisible into constituent corpuscles. From this he concocted a plum-pudding model for atoms. To explain the overall neutral charge of an atom, as contrasted to the corpuscle (electron) negative charge, Thomson proposed that corpuscles floated in a sea of positive charges, with electrons embedded like plums in a pudding; though Thomson’s model posited rapidly moving corpuscles instead of plopped plums.
One of Thomson’s pupils, English physicist and chemist Ernest Rutherford, disproved Thomas’ atomic plum pudding in 1909. In its place, Rutherford imagined in 1911 a planetary atomic model: a cloud of negatively charged electrons swirling in orbits over a compact positively charged nucleus.
Rutherford was working with Danish physicist Niels Bohr, who conjectured in 1913 that electrons moved in specific orbits, which were regulated by Planck’s quantum of action. By 1921, Rutherford and Bohr had come up with an atomic model comprising protons, neutrons, and electrons. This model was validated in the 1950s, when atomic nuclei were manually disassembled by newly developed subatomic particle accelerators and detectors.