Arnold Sommerfeld (1868-1951) was a German physicist who significantly contributed to the development of quantum theory and atomic physics.

An atomic number is a unique identifier for each chemical element.

Carbon-12 (12C) is the most abundant of the two stable isotopes of carbon (carbon-13 being the other), amounting to 98.

A chemical element is a pure substance that is composed of atoms with the same number of protons in their atomic nuclei.

A chemist (from Greek chēm(ía) alchemy; replacing chymist from Medieval Latin alchemist) is a graduated scientist trained in the study of chemistry, or an officially enrolled student in the relevant field.

The Dirac Equation is a fundamental equation in quantum mechanics that describes the behavior of fermions, particles with half-integer spin, such as electrons.

The Wikipedia page for "Electron" provides a comprehensive summary of the subatomic particle known as an electron.

Emilio Gino Segrè (1 February 1905 - 22 April 1989) was an Italian and naturalized-American physicist and Nobel laureate, who discovered the elements technetium and astatine, and the antiproton, a subatomic antiparticle, for which he was awarded the Nobel Prize in Physics in 1959 along with Owen Chamberlain.