1. History of the Periodic Table of the Elements
(CHEM 1360)
Part 3

3. Lavoisier’s Elements “Elements in the body” “Nonmetallic elements”
“Earths”

4. “Atoms are featureless
spheres. The only
difference between
different elements
is their weight.
For example:
Hydrogen 1
Carbon 5
Oxygen 7
Phosphorus 9
Sulphur 13
Magnesia 20
Lime 24
Potash 42
Iron 50
Lead 90
Mercury 167
Gold 190”
John Dalton
Manchester, England
1810

5. These are models of atoms constructed by Dalton,
now on display in a Manchester museum.

6. Determined
Atomic
Weights Accurately
Jöns Jacob Berzelius
Stockholm, Sweden
1826

7. Atomic Weights (Berzelius*)
H Li Be B C N O F Na Mg Al Si P S Cl K Ca Ti V Cr Mn Fe Co Ni Cu Zn As Se Br Rb Sr Y Zr Nb Mo Ru Rh Pd Ag Cd In Sn Sb 122
Te I Cs Ba 137
Di Ce Er La 180
Ta W Os Ir 197
Pt Au Hg Tl 204
Pb Bi Th U 240
*Recalculated using Cannizzaro’s principle

8. “Triads” suggest an underlying pattern
Ca = Sr = Ba = 137
(40+137)/2 = 88.5
Cl = Br = I = 127
( )/2 = 81.2
K = Rb = Cs = 133
(39+133)/2 = 86
S = Se = Te = 125
(32+125)/2 = 78.5
Johann Döbereiner
Jena, Germany
1829
P = As = Sb = 122
(31+122)/2 = 76.5

9. The Chemical Congress of 1860
Ständehaus, Karlsruhe, Germany
The time had come for chemists to resolve several questions and
to come to agreement on several conventions.
While Lincoln was debating key issues during the
Presidential campaign in the fall of 1860, chemists
from all over the world congregated in Karlsruhe.

10. The Chemical Congress debated several key issues. Foremost were
(1) the question of whether to use
chemical equivalents (the amount
of an element that reacts with a
standard weight of oxygen) or
atomic weights to describe
chemical reactions, and (2) what
symbolism to use for chemical
formulas.
Chemical formula symbols were particularly confusing; various
conventions were in use, utilizing bars, dots, sometimes
equivalents and sometimes weights. H2O2 could represent either
water or hydrogen peroxide, C2H4 either ethylene or methane!

11. Cannizzaro provides the solution
Stanislao Cannizzaro wrote a famous pamphlet which was
distributed at the Chemical Congress which clearly distinguished
between atoms and molecules and allowed an unequivocal
working definition of atomic weight. Almost immediately
everyone was converted to his system, which we use today.
Cannizzaro based his suggestions on Avogadro’s hypothesis.

12. Avogadro’s hypothesis is “rediscovered”
Cannizzaro “rediscovered”
Avogadro’s work on gas
volumes which had been
ignored for half a century.
Amedeo Avogadro was far ahead of his time when he published
in 1811 his hypothesis that equal volumes of all gases contain equal
numbers of molecules (at the same temperature and pressure).
Cannizzaro showed that application of Avogadro’s hypothesis
produced a self-consistent set of atomic weights.

13. A word more about volumes of gases. . .
Gay-Lussac had found in 1808 that when gases
chemically react, the volumes of both the reactants
and the products are in simple ratios. For example,
1 volume nitrogen + 3 volumes hydrogen
react to give 2 volumes of ammonia. N + Am Am H H H
Avogadro interpreted this reaction as expressing
what happens on an atomic (and molecular) scale,
by borrowing from Dalton’s atomic theory:

14. And a final word about water. . .
Avogadro in 1811 actually hypothesized the
correct interpretation in the reaction of
hydrogen with oxygen to produce water. O + H H Wa Wa
Again, Avogadro explained this reaction as expressing what happens on an atomic (and molecular) scale, using Dalton’s atomic theory:

15. Another kind of information which helped
Cannizzaro was Dulong-Petit’s law, which was
useful for solids. It stated that the gram atomic heat capacity is constant. That is, the specific
heat (heat required to warm a substance by one degree) is inversely to the atomic weight.
sp. heat at. wt. sp. ht. x at. wt.
(O=1) Bi Pb Au Pt Sn Ag Zn
sp. heat at. wt. sp. ht. x at. wt.
(O=1) Te Cu Ni Fe Co S

16. 2H2 + O2 2H2O The Cannizzaro Principle
The atomic weight of an element is the least weight of it
contained in a (volatile) molecule.
Hydrogen, the lightest gas, is chosen as the standard,
and the atomic weight of hydrogen is set at 1.
Since the molecule of hydrogen weighs twice as much as the
least amount in various compounds (e.g., HCl), then the
molecule of hydrogen contains two atoms, and its chemical
formula may be set as H2. Since two volumes of hydrogen
react with one volume of oxygen to give two volumes of
water, then it may be unequivocally concluded that
2H2 + O H2O

17. The two future discoverers of the Periodic Table, after reading
Cannizzaro’s Pamphlet at the Chemical Congress, stated:
“I well remember how great was the difference
of opinion, and how a compromise was advocated
with great acumen by many scientific men
In the spirit of freedom. . . A compromise was
not arrived at, nor ought it to have been,
but instead the truth. . . [which] soon afterwards
convinced all minds.” — Dmitri Mendeleev
“. . . The scales fell from my eyes, doubts
vanished, and a feeling of calm certainty
came in their place.” — Lothar Meyer

18. The Discovery of the Modern Periodic Table
Dimitri Mendeleev
Lothar Meyer
Two scientists independently discovered
the “modern” Periodic Table in 1869.

19. Mendeleév on his desk played and arranged pieces of paper,
Dimitri Mendeleév
St. Petersburg,
Russia
Mendeleév on his desk played and arranged pieces of paper,
listing elements with their respective atomic weights,
trying to find some order.

20. Mendeleev’s First Table — March, 1869
Ti Zr ?100
V Nb Ta 182
Cr Mo W 186
Mn Rh Pt 197.4
Fe Ru Ir 198
Ni=Co Pd Os 199
H Cu Ag Hg 200
Be Mg Zn Cd 112
B Al ? U Au 197?
C Si ? Sn 118
N P As Sb Bi 210?
O S Se Te 128?
F Cl Br I 127
Li Na K Rb Cs Tl 204
Ca Sr Ba Pb 207
? Ce 92
Er? La 94
Yt? Di 95
In 75.6? Th 118?

21. Mendeleev made 8 statements about his Table in his first publication
1. When arranged by atomic weight, the elements show a
periodicity of properties.
2. Similar elements have atomic weights which are either very
similar (platinum, iridium, osmium) or which increase regularly
(potassium, rubidium, cesium).
3. The arrangement of the elements correspond to their valences.
4. Elements which are most common have small atomic weights.
5. The atomic weight can determine the character of an element.
6. More elements will be discovered.
7. The atomic weight of an element may be corrected by
comparison with adjacent elements.
8. Some properties of unknown elements can be predicted from
their atomic weights.

22. Lothar Meyer’s Table — December, 1869
I II III IV V VI VII VIII IX
B Al — — ? In Tl 202.7
C Si — Sn — Pb 206.4
Ti Zr 89.7
N P As Sb Bi 207.5
V Nb Ta 182.2
O S Se Te 128?
Cr Mo W 183.5
F Cl Br I 126.5
Mn Ru Os 198.6?
Fe Rh Ir 196.7
Co&Ni Pd Pt 196.7
Li Na K Rb Cs 132.7
Cu Ag Au 196.2
?Be Mg Ca Sr Ba 136.8
Zn Cd Hg 199.8

23. Lothar Meyer’s plot Atomic volume Atomic weight
Lothar Meyer’s plot shows definite spikes in an ascending cyclic
pattern that suggests an internal structure. The intriguing
question of atomic structure had to wait for another half century,
until spectroscopists and theoreticians could attack the problem.

24. Differences between Mendeleev and Meyer
1. Mendeleev did not concern himself with why the table worked.
He just boldly proclaimed that the trends were real, and that
in fact the properties of unknown elements could be predicted!
2. Meyer was not so daring about the predictive power of the
table. He was very curious, however, with the reasons for the
trends, which he thought reflected some internal structure.
3. Mendeleev thought the elements were primordial matter.
4. Meyer thought there must be yet smaller particles.
5. Mendeleev continued to work on his table, which very
quickly was successful in predicting specific elements —
and he became famous.
6. It took scientists many decades understand exactly how
Meyer’s plot described an inner structure of the atom, and
his work was eclipsed by these scientists who discovered this
structure of protons, electrons, and neutrons.

25. ? ? ? ? ? ? ? eka-boron eka-aluminum eka-silicon Predicted!
Correct value? ? ? ? ? ?
Misfits? ? ?

26. How Mendeleev predicted unknown elements
Mendeleev simply followed the trends of the table to interpolate
the properties of three new elements, which he called eka-boron,
eka-aluminum, and eka-silicon. He predicted the atomic
weights would be 44, 68, and 72, respectively, and he predicted
the chemical properties and physical properties of each of these
elements.
His paper didn’t get much attention until
Eka-B 44
Eka-Al 68
Eka-Si 72

27. Boisbaudran discovers eka-aluminum
Predicted Found
at. wt. = at. wt. = 69.9
sp. gr. = sp. gr. = 5.94
low m.p m.p. = 30º
Oxide Ea2O Oxide Ga2O3
soluble in acids soluble in acids
and bases and bases
Lecoq
de Boisbaudran,
Cognac, France
Gallium - discovered 1875

28. Nilson discovers eka-boron
Predicted Found
at. wt. = at. wt. = 44
Oxide Eb2O Oxide Sc2O3
with sp. gr. = with sp.gr. =
3.5, not soluble , not soluble
in alkalies in alkalies
Lars Fredrik Nilson,
Uppsala, Sweden
Scandium - discovered 1879

29. Winkler discovers eka-silicon
Predicted Found
at. wt. = at. wt. = 72.3
Oxide EsO Oxide GeO2
with sp. gr. = with sp. gr. =
Volatile chloride GeCl4 with
EsCl b.p. = 86 º
Clemens Winkler,
Freiberg, Germany
Germanium - discovered 1886

31. Sir William Ramsey University College (London)
A new family of elements?!
Sir William Ramsey University College (London)
New gas
isolated from
the atmosphere!

32. A new column is needed for the new element!

33. Another gas discovered! (was originally seen in the sun)

34. Two more gases discovered!

35. Another gas discovered ! (Table needs to be restacked)

37. Brauner attempted to find order in the higher elements
Bohuslav Brauner
Prague, Bohemia
Predicted?!
Bauner predicted 98 elements through uranium

38. A further complication — Rutherford
discovers the “transmutation” of elements
In Ernest Rutherford discovered that radium decays through a series of steps, leading apparently to a new group of elements: Ra Rn Ra-A Ra-B Ra-C Ra-E Ra-F Ra-G

39. A glut of new elements?!
Rutherford’s finding led to the discoveries by other invesigators of a plethora of new elements in other decay schemes during the first decade of These elements included: “ionium,” “brevium,” “actinouranium,” “radiothorium,” “niton,” “actinon,” “thorium-X,” “uranium-X,” and dozens more.
The confusing feature of all these newly discovered elements was that in many instances some of them had very similar, and perhaps identical, chemical properties — even though they had different half-lives.

40. Soddy solves the problem
In 1913 Soddy conceived the idea of an “isotope.” Isotopes (from Greek “isos” meaning “same,” and “topos” meaning “place”) are “in the same place” in the Periodic Table and yet have different nuclear properties. Thus, for example, the “brevium” of Fajans, the “ekatantalum” of Soddy, and the “protactinium” of Hahn and Meitner all belong in the same slot in the Periodic Table — they are isotopes of the same element (protactinium).

41. This was the best guess by 1907 — but it was still not known how many elements actually existed until

42. Moseley — 1912 Henry Moseley Oxford, England
Where N = atomic number of element
v = 1/λ = wavenumber of Kα X-ray line
v0 = Rydberg constant

43. Moseley predicted the following elements were yet to be discovered:
From Moseley’s work, scientists now knew that there were exactly 92 elements ranging from hydrogen to uranium.
Moseley predicted the following elements were yet to be discovered:
43, 61, 75, 85, 87
And using quantum theory, Bohr was ready to propose the modern form of the Periodic Table

44. Niels Bohr
Copenhagen, Denmark

45. Glenn Seaborg Berkeley, California
1937
Only one left to be discovered!
1940
1939

46. Promethium was discovered in an atomic pile in Oak Ridge, Tennessee (1945)
And the transuranium elements were discovered by Seaborg and others

47. Today

48. That’s All Folks!