Models of an atom and old quantum theory

• Thompson modeled an atom as a sphere of radius ∼ 1Å (typical atom radius) lled uniformly by a cloud of positive charge Ze. Inside this cloud there are Z point-like electrons which sit still at their equilibrium positions determined by Coulomb forces. Under various circumstances, for example at by raising temperature, electrons can be excited into vibrating or orbiting motion. Such accelerated motion of charge leads to emission of electromagnetic radiation according to Maxwell equations, which can qualitatively explain why atoms radiate. The model can also describe ejection of electrons from atoms.