106 BELL SYSTEM TECLINICAL JOURNAL 



atom; but they did not. This result is commonly regarded as the 

 strongest evidence for the belief that the Quantum Conditions valid 

 for an atom with one electron are not valid for an atom with two. 



The atom-model faxored I)\- Kramers, and hence presumptively by 

 Bohr, to represent a helium atom in its normal state, involves two 

 electrons moving in orbits which are not coplanar nor even plane. 

 Planes tangent to the two surfaces upon which the orbits are traced 

 intersect each other at 120' along a line passing through the nucleus, 

 and the electrons pass simultaneously across this line at opposite 

 crossing-points. These orbits conform to the Quantum Conditions; 

 and the resultant of the angular momenta of the two electrons, which 

 is the angular momentum of the entire atom, is equal to h/2Tv. This 

 atom-model likewise fails to have the right energy-value for the 

 normal state. 



P. Interpretation of the Optical Spectra of 

 Alkali-Metal Atoms 



The alkali metals (lithium, sodium, potassium, rubidium and 

 caesium) are elements of which the atoms are easily deprived of a 

 single electron apiece; one electron of each atom is, as the phrase 

 goes, exceptionally "loosely bound." Many facts combine to indi- 

 cate this; for instance, each of these elements enters with violence 

 into chemical combinations, and the compounds which each forms are 

 such as to suggest that its atom yields up one electron to the atom or 

 atoms which join with it. Again, when a salt of one of these metals 

 is dissolved, the molecules split up and the atoms of the metal are left 

 wandering around in the solvent minus one electron apiece, while 

 the atoms of the other element each hold on to one captured electron. 

 More definite yet is the direct evidence that the ionizing potentials 

 of the alkali metals are lower than those of any other elements in the 

 same rows of the Periodic Table, those of rubidium and caesium being 

 altogether the smallest known. These alkali metals follow, in the 

 Periodic Table, immediately after the five noble gases helium, neon, 

 argon, xenon and krypton respectively. These gases are chemically 

 all but absolutely inert, almost never entering into combinations. 

 Their ionizing-potentials are higher than those of any other elements 

 in their respective rows of the periodic table, and those of helium 

 and neon are the greatest known. The atoms of each of the alkali 

 metals are much larger than those of the preceding inert gas. 



From all these facts the inference is drawn, that the atom of each 

 inert gas consists of a nucleus and electrons, at least the outermost 



