History of the Periodic Table of the Elements

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History of the Periodic Table of the
Elements (CHEM 1360) Part 3
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Lavoisiers Elements
Elements in the body
Nonmetallic elements
Metallic elements
Earths
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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
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These are models of atoms constructed by
Dalton, now on display in a Manchester museum.
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Determined Atomic Weights Accurately
Jöns Jacob Berzelius Stockholm, Sweden 1826
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Atomic Weights (Berzelius)
H 1 Li 7 Be 9.4 B
11 C 12 N 14 O 16
F 19 Na 23 Mg 24
Al 27.3 Si 28 P 31
S 32 Cl 35.5 K 39
Ca 40 Ti 48 V 51 Cr
52 Mn 55 Fe 56 Co 59
Ni 59 Cu 63 Zn 65
As 75 Se 78 Br 80
Rb 85 Sr 87 Y 88 Zr
90 Nb 94 Mo 96 Ru 104
Rh 104 Pd 106 Ag 108
Cd 112 In 113 Sn 118
Sb 122 Te 125 I 127
Cs 133 Ba 137 Di 138 Ce 140
Er 178 La 180 Ta 182 W
184 Os 195 Ir 197 Pt 198
Au 199 Hg 200 Tl 204 Pb 207
Bi 208 Th 231 U 240
Recalculated using Cannizzaros principle
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Triads suggest an underlying pattern
Ca 40 Sr 87 Ba 137 (40137)/2
88.5
Cl 35.5 Br 80 I 127 (35.5127)/2
81.2
K 39 Rb 85 Cs 133 (39133)/2 86
S 32 Se 78 Te 125 (32125)/2 78.5
Johann Döbereiner Jena, Germany 1829
P 31 As 75 Sb 122 (31122)/2 76.5
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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.
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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!
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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 Avogadros hypothesis.
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Avogadros hypothesis is rediscovered
Cannizzaro rediscovered Avogadros 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 Avogadros
hypothesis produced a self-consistent set of
atomic weights.
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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.
Am
Am

N
H
H
H
Avogadro interpreted this reaction as expressing
what happens on an atomic (and molecular)
scale, by borrowing from Daltons atomic
theory
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And a final word about water. . .
Avogadro in 1811 actually hypothesized
the correct interpretation in the reaction
of hydrogen with oxygen to produce water.

Wa
O
H
H
Wa
Again, Avogadro explained this reaction as
expressing what happens on an atomic (and
molecular) scale, using Daltons atomic
theory
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Another kind of information which
helped Cannizzaro was Dulong-Petits 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.
(O1) Te 0.0912 4.03
0.3675 Cu 0.0949 3.957
0.3755 Ni 0.1035 3.69 0.3819 Fe
0.1100 3.392 0.3731 Co 0.1498
2.46 0.3685 S 0.1880 2.011
0.3780
sp. heat at. wt. sp. ht. x at. wt.
(O1) Bi 0.0288 13.30
0.3830 Pb 0.0293 12.95
0.3794 Au 0.0298 12.43 0.3704 Pt
0.0314 11.16 0.3740 Sn 0.0514
7.35 0.3779 Ag 0.0557 6.75
0.3759 Zn 0.0927 4.03
0.3736
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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 O2
2H2O
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The two future discoverers of the Periodic Table,
after reading Cannizzaros 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
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The Discovery of the Modern Periodic Table
Dimitri Mendeleev
Lothar Meyer
Two scientists independently discovered the
modern Periodic Table in 1869.
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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.
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Mendeleevs First Table March, 1869

Ti 50 Zr 90 ?100

V 51 Nb 94 Ta 182

Cr 52 Mo 96 W 186
Mn 55
Rh 104.4 Pt 197.4
Fe 56
Ru 104.4 Ir 198
NiCo 59 Pd
106.6 Os 199 H 1
Cu 63.4 Ag 108
Hg 200 Be 9.4 Mg 24
Zn 65.2 Cd 112 B
11 Al 27.4 ? 68 U
116 Au 197? C 12
Si 28 ? 70 Sn 118
N 14 P 31
As 75 Sb 122 Bi 210?
O 16 S 32 Se 79.4
Te 128? F 19
Cl 35.5 Br 80 I 127 Li 7
Na 23 K 39 Rb 85.4
Cs 133 Tl 204
Ca 40 Sr 87.6 Ba 137
Pb 207
? 45 Ce 92
Er? 56 La 94
Yt? 60 Di 95
In 75.6?
Th 118?
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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.
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Lothar Meyers Table December, 1869
I II III IV
V VI VII VIII IX
B 11 Al 27.3
? In 113.4
Tl 202.7 C 11.97 Si 28
Sn 117.8
Pb 206.4
Ti 48 Zr
89.7 N 14.01 P 30.9
As 74.9 Sb 122.1
Bi 207.5
V 51.2 Nb 93.7
Ta 182.2 O 15.96
S 31.98 Se 78.0
Te 128?
Cr 52.4 Mo 95.6
W 183.5 F 19.1 Cl
35.38 Br 79.75 I
126.5
Mn 54.8 Ru 103.5
Os 198.6?
Fe 55.9 Rh 104.1
Ir 196.7
CoNi 58.6 Pd 106.2
Pt 196.7 Li 7.01 Na 22.99 K
39.04 Rb 85.2 Cs
132.7
Cu 63.3 Ag 107.66
Au 196.2 ?Be 9.7 Mg 23.9 Ca39.9
Sr 87.0 Ba 136.8
Zn 64.9
Cd 111.6 Hg 199.8
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Lothar Meyers plot
Atomic volume
Atomic weight
Lothar Meyers 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.
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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 Meyers 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.
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eka-boron eka-aluminum eka-silicon
Predicted!
Correct value?
?
?
?
?
?
Misfits?
?
?
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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 didnt get much
attention until. . . .
Eka-Si 72
Eka-Al 68
Eka-B 44
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Boisbaudran discovers eka-aluminum
Predicted Found at. wt. 68
at. wt. 69.9 sp. gr. 5.9
sp. gr. 5.94 low m.p. m.p.
30º Oxide Ea2O3 Oxide Ga2O3 soluble in
acids soluble in acids and bases
and bases
Lecoq de Boisbaudran, Cognac, France
Gallium - discovered 1875
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Nilson discovers eka-boron
Predicted Found at. wt. 44
at. wt. 44 Oxide Eb2O3 Oxide
Sc2O3 with sp. gr. with sp.gr. 3.5,
not soluble 3.86, not soluble in alkalies
in alkalies
Lars Fredrik Nilson, Uppsala, Sweden
Scandium - discovered 1879
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Winkler discovers eka-silicon
Predicted Found at. wt. 72
at. wt. 72.3 Oxide EsO2
Oxide GeO2 with sp. gr. with sp. gr.
4.7
4.70 Volatile chloride GeCl4 with EsCl4
b.p. 86 º
Clemens Winkler, Freiberg, Germany
Germanium - discovered 1886
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A new family of elements?!
New gas isolated from the atmosphere!
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A new column is needed for the new element!
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Another gas discovered! (was originally seen in
the sun)
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Two more gases discovered!
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Another gas discovered ! (Table needs to be
restacked)
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Brauner attempted to find order in the higher
elements
Bohuslav Brauner Prague, Bohemia
Predicted?!
Bauner predicted 98 elements through uranium
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A further complication Rutherford discovers the
transmutation of elements
In 1902-1905 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
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A glut of new elements?!
Rutherfords finding led to the discoveries by
other invesigators of a plethora of new elements
in other decay schemes during the first decade of
1900. 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.
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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).
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This was the best guess by 1907 but it was
still not known how many elements actually
existed. . . . until. . . . .
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Moseley 1912
Henry Moseley Oxford, England
Where N atomic number of element v 1/?
wavenumber of Ka X-ray
line v0 Rydberg constant
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From Moseleys 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. .
. .
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Niels Bohr Copenhagen, Denmark
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Glenn Seaborg Berkeley, California
1937
Only one left to be discovered!
1940
1939
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Promethium was discovered in an atomic pile in
Oak Ridge, Tennessee (1945)
And the transuranium elements were discovered by
Seaborg and others. . . .
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Today. . . .
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Thats All Folks!