Electron Theory of Chemistry to Solids, 751 



with a singly-charged sodium atom in one cell and a chlorine 

 atom with a positive charge of 7 in the adjacent ones, but 

 that the chlorine atom instead of losing all its seven electrons 

 •to form the outer walls of the cell only uses one, and the 

 other six electrons and the atom with seven charges form a 

 unit having unit positive charge ; so that the structure of 

 the cell for sodium chloride would be represented by a 

 sodium atom at the centre of one cell and a chlorine atom 

 •surrounded by six electrons arranged as a regular octahedron 

 considerably smaller than the cube at the centres of adjacent 

 •cells. This arrangement is in some respects more symme- 

 trical than the other, for in it we have what is equivalent to 

 a unit positive charge at the centre of each cell ; in the other 

 arrangement there is a unit positive charge in one cell and a 

 positive charge of seven in the adjacent cell. Thus an electron 

 tit the centre of a face would be pulled one way by a charge 

 of seven and in the opposite way by a charge of one. The 

 result would be that the electron would be displaced ; the 

 face-centred cubes would become cubes with pyramids on 

 their faces, the pyramids being convex for one set of tubes 

 and concave for the other. 



If we regard the chlorine cell as equivalent to a mono- 

 valent one, we can find the difference between the energy of 

 n gramme molecule of sodium chloride and the energy of the 

 sodium and chlorine before combination. 



By the equation (9) on p. 737 the energy of 23, grammes 

 of sodium is 



-2-07xl0 ] 



/A\ 1/3 

 \2S) ' 



where A = '971?is the density of metallic sodium. Thus the 

 energy of: the sodium before combination is 



-2*07 x -348 xlO 13 ; 



after combination the energy is 



2A 3 ~> w» 



2-07 x 10 13 



»r- 



23 + 35- 



where A! = 2'17 is the density of sodium chloride. The 

 •energy after combination is thus 



-2-07 x -4213 xlO 13 . 

 The energy of the chlorine before combination is 



/ A 2 V /3 



\35*5, 



where A 2 is the density of liquid chlorine, A 2 = 1*558 at 



