﻿Frequency 
  cuul 
  Molecular 
  Number. 
  455 
  

  

  Lead 
  Compounds 
  (N 
  = 
  82). 
  

  

  Name. 
  Formula. 
  N. 
  vXlO"" 
  12 
  . 
  NvXlO 
  -12 
  . 
  

   Lead 
  

  

  bromide 
  PbBr 
  152 
  1067 
  8 
  x203 
  

  

  chloride 
  PbCl^ 
  116 
  1-414 
  8 
  x20-5 
  

  

  iodide 
  PbL, 
  188 
  0-863 
  8 
  x203 
  

  

  oxide 
  PbO 
  90 
  2-443 
  10^x210 
  

  

  selenide 
  PbSe 
  116 
  2'029 
  11 
  X21'4 
  

  

  sulphate 
  PbS0 
  4 
  130 
  1-795 
  11 
  X21-2 
  

  

  sulphide 
  PbS 
  98 
  2*274 
  10JX2P2 
  

  

  Thorium 
  Compound 
  (N 
  = 
  90). 
  

   Thorium 
  

  

  chloride 
  ThCl 
  4 
  158 
  P214 
  9x2P3 
  

  

  Gkoup 
  V. 
  

  

  Almost 
  all 
  the 
  compounds 
  so 
  far 
  considered 
  have 
  been 
  

   metallic 
  salts. 
  In 
  the 
  fifth 
  group 
  a 
  number 
  of 
  non-metallic 
  

   compounds 
  are 
  met 
  with 
  ; 
  and 
  although 
  many 
  of 
  these 
  

   conform 
  to 
  the 
  proposed 
  relation 
  with 
  frequency 
  numbers 
  n 
  

   or 
  n 
  + 
  ^, 
  several 
  require 
  the 
  use 
  of 
  values 
  n 
  + 
  \ 
  or 
  n+ 
  f. 
  It 
  

   is 
  at 
  present 
  impossible 
  to 
  decide 
  whether 
  ihis 
  means 
  that 
  the 
  

   relation 
  fails 
  to 
  hold 
  in 
  these 
  two 
  cases, 
  or 
  whether 
  the 
  

   apparent 
  failure 
  is 
  to 
  be 
  attributed 
  to 
  our 
  ignorance 
  of 
  

   the 
  degree 
  of 
  molecular 
  association 
  in 
  such 
  compounds. 
  It 
  

   may 
  be 
  pointed 
  out 
  that 
  the 
  compounds 
  in 
  question 
  belong 
  

   to 
  the 
  " 
  non-polar 
  " 
  type 
  *. 
  According 
  to 
  Langmuir 
  solid 
  

   polar 
  compounds 
  are 
  built 
  up 
  of 
  atoms 
  bound 
  together 
  by 
  

   secondary 
  valencies, 
  whilst 
  solid 
  non-polar 
  compounds 
  consist 
  

   of 
  " 
  group 
  molecules 
  " 
  in 
  which 
  the 
  atoms 
  ate 
  usually 
  held 
  

   together 
  by 
  primary 
  valencies; 
  these 
  group 
  molecules 
  in 
  turn 
  

   are 
  bound 
  together 
  by 
  secondary 
  valencies 
  to 
  form 
  a 
  large 
  

   " 
  crystal 
  molecule." 
  As 
  data 
  for 
  determining 
  the 
  molecular 
  

   frequency 
  are 
  available 
  for 
  only 
  a 
  small 
  number 
  of 
  inorganic 
  

   non-polar 
  compounds, 
  further 
  discussion 
  may 
  be 
  deferred 
  till 
  

   organic 
  compounds 
  are 
  considered. 
  

  

  Group 
  V. 
  

  

  Nitrogen 
  Compounds 
  (N 
  — 
  7). 
  

  

  Name. 
  Formula. 
  N. 
  vxlO 
  -12 
  . 
  NvXlO 
  -12 
  . 
  

   Nitrogen 
  

  

  cblorophosphide 
  ... 
  N 
  3 
  P 
  3 
  C1 
  168 
  0580 
  4|x21'6 
  

  

  pentoxide 
  N 
  2 
  5 
  54 
  1*278 
  3±x2P2 
  

  

  sulphide 
  N 
  4 
  S 
  4 
  92 
  1-117 
  5x20-5 
  

  

  * 
  See 
  Lang-muir, 
  Amer. 
  Chem. 
  Soc. 
  Journ. 
  vol. 
  xxxviii. 
  p. 
  2221 
  (1916). 
  

  

  