Table 515. 40I 



ELECTRONS, PROTONS, ATOMIC STRUCTURE, MAGNETIC FIELD 



OF ATOMS. 



Free negative electron: (corpuscle, J. J. Thomson); mass = S.gg X 10— 28g= 1/1848 H atom, probably all of elec- 

 trical ori;<in due to inertia of self-induction. 



Theory shows that when speed of electron = i/io velocity of light its mass should be appreciably dependent upon 

 that speed. If OTq be mass for small velocity v, m be the transverse mass for v, v/ (velocity of light) = ^, then m =»»o 

 (i _ (32)4, Lorentz, Einstein; 



for P = o.oi o.io 0.2 0.3 0.4 o.s 0.6 0.7 0.8 0.9 



= i.oooos 1.00s I-02 1.048 1.091 i.iSS 1.250 1.400 1.667 2.294 



(Confirmed by Bucherer, Ann. d. Phys. 1909, Wolz, Ann. d. Phys. Radium ejects electrons with 3/10 to 98/100 velocity 

 of light.) m, due to charge = iE^/sa, E = charge, a = radius, whence radius of electron = 2 X 10-'' cm= 1/50,000 

 atomic radius. Cf. (radius of earth)/(radius of Neptune's orbit) = 1/360,000. 



Evidence from collisions of a-particles indicate that the diameter of the electron cannot be greater than 4 X io->'. 

 (Chadwick and Bieler, Phil. Mag. i92t.) 



Positive Electron or Proton : heavy, extraordinarily small, never found associated with mass less than that of the H 

 atom; mass 1.65 X io--^g. If mass all electrical, radius must be 1/2000 that of the electron. No experimental evidence 

 as with the latter since high enough speeds not available. Penetrability of atom by /3-particle (may penetrate 10,000 

 atomic systems before it happens to detach an electron) and a-particles (8,000 times more massive than — electron, pass 

 through 500,000 atoms without apparent deflection by nucleus more than 2 or 3 times) shows extreme minuteness. 

 Upper limit: not larger than 10-12 cm for Au (heavy atom) and lo-'^ for H (light atom) (Rutherford). Cf. (radius sun) 

 /(radius Neptune's orbit) = 1/3000, but sun is larger than planets. (Hg atoms by billions may pass through thin- 

 walled highly-evacuated glass tubes without impairing vacuum, therefore massive parts of atoms must be extremely 

 small compared to volume of atom.) 



Rutherford Atom : Atoms of all elements are somewhat similarly built. At the center a + charged nucleus of minute 

 dimensions, responsible for most of the mass of the atom ; this is surrounded by a distribution of electrons held in equilib- 

 rium by the force from the nucleus. Resultant nuclear charge = atomic or ordinal no., varies from i for H to 92 for U. 

 "These atomic nos. represent the number of planetary electrons which surround the nucleus. By the action of light, the 

 electric charge, bombardment by o-particles, one or more of the planetary electrons may be driven away from the nu- 

 cleus; by X-rays or the swift /3-rays some of the more strongly bound may be removed. New electrons are generally soon 

 captured to replace these. The nucleus is much more stable and when disrupted (radioactive changes, bombardment 

 with a-particles) shows no tendency to revert to original state. 



Moseley (Phil. Mag. 26, 191 2; 27, 1914) photographed and analyzed X-ray spectra, showing their exact similarity in 

 structure from element to element, differing only in frequencies, the square roots of these frequencies forming an arith- 

 metical progression from element to element. Moseley's series of increasing X-ray frequencies is with one or two excep- 

 tions that of increasing atomic weights, and these exceptions are less anomalous for the X-ray series than for the atomic- 

 weight series. It seems plausible then that there are 92 elements (from H to U) built up by the addition of some electri- 

 cal element. Moseley assigned successive integers to this series (see Table 531) known now as atomic numbers. 



Moseley's discovery may be expressed in the form 



5l = ^1 or -' = ^ 



W2 ^2 ^1 ^2^ 



where E is the nuclear charge and A the wave-length. Substituting for the highest frequency line of W, K2 = 0.167 

 X io~'cm (Hull), £2 = 74 = Nw, and £1 = 1, then \j= highest possible frequency by element which has one + elec- 

 tron; X, = 91.4 nifi. Now the H ultra-violet series highest frequency line = 91.2 m/n (Lyman); i.e., this ultra-violet line 

 of H is nothing but its K X-ray line. Similarly, it seems equally certain that the ordinary Balmer series of H (head at 

 36s mil) is its L X-ray series and Paschen's infra-red series its M X-ray series. 



The application of Newton's law to Moseley's law leads to EJEi = fl'./a,, where the a's are the radii of the inmost — 

 electronic orbits, i.e., the radii of these orbits are inversely proportional to the central charges or atomic numbers. 



There are other negative electrons on the nucleus with corresponding -f charges to make the atom neutral electrically. 

 The negative nuclear charges may serve to hold the positive ones together.^ He, atomic no. = 2, has two free + charges, 

 on nucleus; thev ' us has 4 -)- protons held together by 2 — electrons with 2 — electrons outside nucleus. H has one 

 4- proton and one — electron. 



If the — electron is designated as e (charge — i, mass negligible) and the -f- proton as p (charge ■\- 1, mass i except in 

 H) then the formula for the nucleus of any element from He to U may be written as (p2e)N(pe)D where N is the atomic 

 number and n has values from o to 54. If n be taken as — i, then H may be included. " (Masson, Phil. Mag. 41, 1921.) 

 If brackets are used to designate the nucleus, then the complete element becomes [(p2e)N(pe)iiJ e». In the formation of 

 ions only the part exterior to the brackets is affected. For the a-transformation (emission of -\- charged He nucleus) 

 2(p2e) = (P2e)2/, the sub-chemical equation may be written l(P2e)»(pe)nl e» = l(p2e)i.-2(pe)nleN -f- (p..e)2/ (He nu- 

 cleus); the new elements upon discharge of its - charge becomes |(p2e)N-2(pe)n] eB_2 showing the characteristic a-ray 

 change with the atomic weight lowered by 2 and the mass by 4. The |3-ray 2(pe)= (pjcj-i-e/ gives the equation 

 l(P2e)i<(pe)nleii = [(p2e)ii+i(pe)ii-2)eK-|-e/, mass uncharged and forms the singly — charged ion of an isobar. 



(This Table supplements Table 514.) 



3 Li 3.00 13 Al 2.70 25 Mn 2.9st 36 Kr 2.35* 54 Xe 2.70* 



4 Gl 2.30 14 Si 2.35 26 Fe 2.80 37 Rb 4.50 55 Cs 4.75 



6 C 1. 54 16 S 2.0s 27 Co 2.7s 38 Sr 3.90 56 Ba 4.20 



7 N 1.30 17 CI 2.10 28 Ni 2.70 47 Ag 3.5s 81 Tl 4.50 



8 O 1.30 18 A 2.0S* 29 Cu 2. 75 48 Cd 3.20 82 Pb 3.80 



9 F 1.35 19 K 4.15 30 Zn 2.6s 50 Sn 2.80 83 Bi 2.96 



10 Ne 1.30* 20 Ca 3.40 33 As 2.52 51 Sb 2.80 



11 Na 3.5s 22 Ti 2.80 34 Se 2.35 52 Te 2.65 



12 Mg 2.8s 24 Cr 2.8ot 3S Br 2.38 S3 1 2.80 



• Outer electron shell. t Cr, "electronegative," 2.3s; Mn., ditto, 2.35. 



Broughall (Phil. Mag. 41, p. 872, 1921) computes in the same units from Van der Waal's constant "b" the diameters 

 01 He, N, A, Kr, and X as 2.3, 2.6, 2.9, 3.1, and 3.4. These inert elements correspond to Langmuir's completelv filled 

 successive electron shells. The corresponding atomic numbers are 2, 10, 18, 36 and 54. For Langmuir s theory see J. 

 Am. Ch. Soc, p. 868, 1919, Science 54, p. 59, 1921. 



Smithsonian Tables. 



