﻿of 
  Atoms 
  and 
  Molecules. 
  497 
  

  

  for 
  the 
  electrons 
  will 
  involve 
  a 
  variation 
  in 
  the 
  dimensions 
  

   of 
  the 
  outer 
  ring- 
  similar 
  to 
  the 
  variation 
  in 
  the 
  atomic 
  

   volumes 
  of 
  the 
  corresponding 
  elements. 
  It 
  must, 
  however, 
  

   be 
  borne 
  in 
  mind 
  that 
  the 
  experimental 
  determinations 
  of 
  

   atomic 
  volumes 
  in 
  most 
  cases 
  are 
  deduced 
  from 
  consideration 
  

   of 
  molecules 
  rather 
  than 
  atoms. 
  

  

  From 
  the 
  above 
  we 
  are 
  led 
  to 
  the 
  following 
  possible 
  scheme 
  

   for 
  the 
  arrangement 
  of 
  the 
  electrons 
  in 
  light 
  atoms: 
  — 
  

  

  1(1) 
  

  

  9 
  (4, 
  4, 
  1) 
  

  

  17(8,4,4,1) 
  

  

  2(2) 
  

  

  10(8,2) 
  

  

  18(8,8,2) 
  

  

  3(2,1) 
  

  

  11(8,2,1) 
  

  

  19(8,8,2,1) 
  

  

  4(2,2) 
  

  

  12(8,2,2) 
  

  

  20(8,8,2,2} 
  

  

  5(2,3) 
  

  

  13(8,2,3) 
  

  

  21(8,8,2,3) 
  

  

  6(2,4) 
  

  

  14(8,2,4) 
  

  

  22(8,8,2,4) 
  

  

  7(4,3) 
  

  

  15(8,4,3) 
  

  

  23(8,8,4,3) 
  

  

  8(4,2,2) 
  

  

  16(8,4,2,2) 
  

  

  24 
  (8, 
  8, 
  4, 
  2, 
  2) 
  

  

  Without 
  any 
  fuller 
  discussion 
  it 
  seems 
  not 
  unlikely 
  that 
  

   this 
  constitution 
  of 
  the 
  atoms 
  will 
  correspond 
  to 
  properties 
  of 
  

   the 
  elements 
  similar 
  with 
  those 
  observed. 
  

  

  In 
  the 
  first 
  place 
  there 
  will 
  be 
  a 
  marked 
  periodicity 
  with 
  

   a 
  period 
  of 
  8. 
  Further, 
  the 
  binding 
  of 
  the 
  outer 
  electrons 
  

   in 
  every 
  horizontal 
  series 
  of 
  the 
  above 
  scheme 
  will 
  become 
  

   weaker 
  with 
  increasing 
  number 
  of 
  electrons 
  per 
  atom, 
  corre- 
  

   sponding 
  to 
  the 
  observed 
  increase 
  of 
  the 
  electropositive 
  

   character 
  for 
  an 
  increase 
  of 
  atomic 
  weight 
  of 
  the 
  elements 
  

   in 
  every 
  single 
  group 
  of 
  the- 
  periodic 
  system. 
  A 
  corre- 
  

   sponding 
  agreement 
  holds 
  for 
  the 
  variation 
  of 
  the 
  atomic 
  

   volumes. 
  

  

  In 
  the 
  case 
  of 
  atoms 
  of 
  higher 
  atomic 
  weight 
  the 
  simple 
  

   assumptions 
  used 
  do 
  not 
  apply. 
  A 
  few 
  indications, 
  however, 
  

   are 
  suggested 
  from 
  consideration 
  of 
  the 
  variations 
  in 
  the 
  

   chemical 
  properties 
  of 
  the 
  elements. 
  At 
  the 
  end 
  of 
  the 
  3rd 
  

   period 
  of 
  8 
  elements 
  we 
  meet 
  with 
  the 
  iron-group. 
  This 
  

   group 
  takes 
  a 
  particular 
  position 
  in 
  the 
  system 
  of 
  the 
  

   elements, 
  since 
  it 
  is 
  the 
  first 
  time 
  that 
  elements 
  of 
  neigh- 
  

   bouring 
  atomic 
  weights 
  show 
  similar 
  chemical 
  properties. 
  

   This 
  circumstance 
  indicates 
  that 
  the 
  configurations 
  of 
  the 
  

   electrons 
  in 
  the 
  elements 
  of 
  this 
  group 
  differ 
  only 
  in 
  

   the 
  arrangement 
  of 
  the 
  inner 
  electrons. 
  The 
  fact 
  that 
  the 
  

   period 
  in 
  the 
  chemical 
  properties 
  of 
  the 
  elements 
  after 
  

   the 
  iron-group 
  is 
  no 
  longer 
  8, 
  but 
  18, 
  suggests 
  that 
  elements 
  

   of 
  higher 
  atomic 
  weight 
  contain 
  a 
  recurrent 
  configuration 
  

   of 
  18 
  electrons 
  in 
  the 
  innermost 
  rings. 
  The 
  deviation 
  from 
  

  

  