Use the drop-down menus to complete the statements. are pure substances that cannot be broken down into a simpler form. are units of two or more atoms. are the smallest possible particles of an element. are pure substances made of two or more atoms of different elements.

The nuclear potential that binds protons and neutrons in the nucleus of an atom is often approximated by a square well. imagine a proton conned in an innite square well of length 105 nm, a typical nuclear diameter. calculate the wavelength and energy associated with the photon that is emitted when the proton undergoes a transition from the rst excited state (n 2) to the ground state (n 1). in what region of the electromagnetic spectrum does this wavelength belong?