﻿NEW 
  CHEMICAL 
  ELEMENTS 
  BLIGH 
  247 
  

  

  chemically. 
  Moseley's 
  relation 
  revealed 
  gaps 
  in 
  the 
  sequence 
  of 
  

   atomic 
  numbers 
  as 
  determined 
  by 
  spectroscopic 
  data, 
  and 
  these 
  gaps 
  

   indicated 
  undiscovered 
  elements, 
  agreeing 
  in 
  every 
  case 
  with 
  those 
  

   predicted 
  by 
  the 
  periodic 
  table, 
  but 
  with 
  the 
  addition 
  of 
  a 
  gap 
  No. 
  61 
  

   among 
  the 
  rare 
  earths. 
  Moreover 
  the 
  relation 
  actually 
  made 
  it 
  

   possible 
  to 
  calculate 
  in 
  advance 
  the 
  line 
  frequency 
  for 
  the 
  undis- 
  

   covered 
  elements, 
  and 
  thus 
  provided 
  a 
  most 
  definite 
  means 
  of 
  testing 
  

   the 
  claim 
  of 
  any 
  newly 
  discovered 
  substance 
  to 
  be 
  regarded 
  as 
  a 
  miss- 
  

   ing 
  element, 
  and 
  of 
  identifying 
  its 
  nature 
  and 
  position. 
  The 
  definite 
  

   utility 
  of 
  this 
  principle 
  will 
  be 
  noted 
  in 
  a 
  subsequent 
  section 
  of 
  this 
  

   survey. 
  At 
  this 
  time 
  (1913-14) 
  gaps 
  in 
  the 
  table 
  indicated 
  missing 
  

   elements 
  as 
  follows 
  : 
  43 
  and 
  75, 
  analogues 
  of 
  manganese 
  ; 
  61 
  , 
  a 
  rare 
  earth 
  

   element; 
  85, 
  a 
  halogen; 
  87, 
  an 
  alkali 
  metal, 
  and 
  an 
  element 
  91 
  . 
  Mose- 
  

   ley 
  assumed 
  that 
  72 
  was 
  filled 
  by 
  celtium, 
  which 
  as 
  will 
  subsequently 
  

   be 
  seen 
  was 
  not 
  the 
  case. 
  According 
  to 
  the 
  work 
  of 
  Soddy, 
  Hahn, 
  and 
  

   Meitner 
  (1918), 
  91 
  is 
  considered 
  to 
  be 
  filled 
  by 
  a 
  radioactive 
  product, 
  

   protoactinium, 
  in 
  the 
  actinium 
  series. 
  Moseley's 
  principle 
  served 
  to 
  

   settle 
  the 
  tota,l 
  number 
  of 
  possible 
  elements 
  with 
  a 
  finahty 
  which 
  

   would 
  never 
  have 
  been 
  possible 
  from 
  a 
  classification 
  built 
  only 
  on 
  

   analogies 
  and 
  chemical 
  properties; 
  the 
  fact 
  that 
  the 
  latter 
  more 
  

   indefinite 
  method 
  had 
  overlooked 
  only 
  one 
  element 
  was 
  therefore 
  

   quite 
  fortuitous. 
  The 
  rare 
  earth 
  group 
  of 
  metals, 
  besides 
  being 
  

   difficult 
  of 
  separation, 
  contained 
  in 
  itself 
  no 
  conclusive 
  indication 
  of 
  

   the 
  number 
  of 
  elements 
  which 
  it 
  contained 
  so 
  that 
  Moseley's 
  work 
  

   settled, 
  in 
  this 
  respect, 
  a 
  troublesome 
  difficulty. 
  It 
  has 
  to 
  be 
  recorded 
  

   with 
  regret 
  that 
  Moseley 
  met 
  his 
  death 
  at 
  Gallipoli 
  in 
  1915 
  at 
  the 
  

   early 
  age 
  of 
  28 
  years. 
  His 
  name 
  has, 
  however, 
  an 
  assured 
  place 
  for 
  

   all 
  time 
  among 
  the 
  pioneers 
  of 
  scientific 
  progress. 
  

  

  A 
  further 
  stage 
  in 
  the 
  advance 
  of 
  chemical 
  theory 
  has 
  now 
  been 
  

   surveyed; 
  the 
  disputed 
  difficulties 
  of 
  the 
  periodic 
  scheme 
  have 
  been 
  

   adjusted 
  in 
  keeping 
  with 
  general 
  developments; 
  an 
  advance 
  has 
  been 
  

   made, 
  but 
  the 
  work 
  of 
  past 
  decades 
  has 
  not 
  been 
  pulled 
  down 
  to 
  be 
  

   reconstructed 
  on 
  other 
  lines, 
  rather 
  have 
  the 
  discordant 
  features 
  of 
  

   this 
  work 
  been 
  gently 
  adjusted 
  to 
  the 
  scheme 
  of 
  nature 
  now 
  more 
  

   clearly 
  revealed. 
  The 
  next 
  stage 
  shows 
  a 
  further 
  striking 
  develop- 
  

   ment 
  in 
  this 
  direction, 
  and 
  is 
  supplied 
  by 
  Bohr's 
  application 
  of 
  the 
  

   quantum 
  theory 
  to 
  atomic 
  structure. 
  As 
  yet 
  there 
  was 
  no 
  indication 
  

   as 
  to 
  whether 
  elements 
  of 
  higher 
  atomic 
  number 
  than 
  uranium 
  (92) 
  

   might 
  possibly 
  exist, 
  nor 
  was 
  there 
  any 
  developed 
  and 
  supported 
  

   scheme 
  for 
  the 
  arrangement 
  of 
  electrons 
  in 
  their 
  orbits, 
  nor 
  any 
  

   fundamental 
  explanation 
  of 
  the 
  well 
  defined 
  periodic 
  groups 
  of 
  

   elements, 
  or 
  of 
  the 
  existence 
  of 
  the 
  rare 
  earth 
  group. 
  Bohr 
  defined 
  

   according 
  to 
  quantum 
  principles 
  the 
  orbits 
  in 
  which 
  electrons 
  should 
  

   be 
  free 
  to 
  move, 
  and 
  evolved 
  a 
  scheme 
  of 
  electron 
  grouping 
  in 
  accord- 
  

   ance 
  with 
  the 
  recurrence 
  of 
  periodic 
  properties, 
  in 
  which 
  the 
  rare 
  

  

  