1. Chapter 5
History of
the
Periodic

2. Chapter 5

3. History of the Periodic
Table
The Periodic Law –
Physical and
Chemical
Properties of
Elements are
Periodic Functions

4. History of the Periodic
Table
The Periodic Law –
Physical and
Chemical
Properties of
Elements are
Periodic Functions

5. The development of the
periodic table begins
with German chemist
Johann Dobereiner
(1780-1849) who
grouped elements based
on similarities.

6. Calcium (atomic mass 40),
strontium (atomic mass 88),
and barium (atomic mass 137)
possess similar chemical
properties.
(Find them on the
Periodic Table)

7. Dobereiner noticed the
atomic mass of strontium fell
midway between the masses
of calcium and barium:
Ca Sr
Ba
40
?? 137
(40 + 137) ÷ 2 = ??

8. Dobereiner noticed the
same pattern for the alkali
metal triad (Li/Na/K) and
the halogen triad (Cl/Br/I).
Li Na K
Cl Br I
7 ?? 39
35 ?? 127

9. (Was this merely a
coincidence or did
some pattern to the
arrangement of the
elements exist?)

10. 1829 Dobereiner proposed
the
Law of Triads:
The middle element in the
triad had atomic mass that
was the average of the other
two members.

11. 1829 Dobereiner proposed
the
Law of Triads:
The middle element in the
triad had atomic mass that
was the average of the other
two members.

12. (Soon other scientists found
chemical relationships extended
beyond triads. Fluorine was added
to Cl/Br/I group; sulfur, oxygen,
selenium and tellurium were
grouped into a family; nitrogen,
phosphorus, arsenic, antimony,
and bismuth were classified as
another group.)

13. First International
Congress of Chemists
Karlsruhe, Germany 1860
-to discuss uniform ways to
measure Atomic Mass and to
solve other communication
problems.
-Only 60 Elements at this time

14. First International
Congress of Chemists
Karlsruhe, Germany 1860
-to discuss uniform ways to
measure Atomic Mass and to
solve other communication
problems.
-Only 60 Elements at this time

15. Demetri Mendeleev 1869
FATHER OF THE
MODERN PERIODIC TABLE
Mendeleev insisted on
ordering elements by
atomic mass, and
grouping them by their
PROPERTIES.

16. Demetri Mendeleev 1869
FATHER OF THE
MODERN PERIODIC TABLE
Mendeleev insisted on
ordering elements by
atomic mass, and
grouping them by their
PROPERTIES.

17. Demetri Mendeleev 1869
FATHER OF THE
MODERN PERIODIC TABLE
Mendeleev insisted on
ordering elements by
atomic mass, and
grouping them by their
PROPERTIES.

18. This resulted in several
"gaps" in the Periodic
Table. Both Gallium (Ga)
and Germanium (Ge)
were unknown at the time
Thus there was a gap under
Aluminum (Al) and a gap
under Silicon (Si)

19. Mendeleev concluded
therefore that there
must be two elements,
which he called
"eka-Aluminum" and
"eka-Silicon" which
must fill these gaps

20. Mendeleev made
predictions on
some of the vacant
spaces in the
Periodic Table.
Such as:
Eka-silicon, (Germainium)
Eka-aluminium, (Gallium)

22. Gallium was
discovered in 1875
by Paul Emile.
Its general
chemistry
matched
Mendeleev's
predictions for

23. Germanium (ekasilicon) was discovered in
1886 by Clemens Winkler.
The agreement with Mendeleev's
predictions are shown in the table below
Property
Ekasilicon
Germanium
72
72.32
Density (g/cc)
5.5
5.47
Atomic volume
13
13.22
Atomic Mass
Outer Shell Electrons (Dots)
Boiling point of GeCl4
/degrees Celsius
4
4
<100
86

24. Henry Moseley 1913
Assistant to Rutherford
(killed at Gallipoli at age 28)
-discovered a mathematical
relationship between the
frequency of X-rays and the
atomic number.

25. Henry Moseley 1913
Assistant to Rutherford
(killed at Gallipoli at age 28)
-discovered a mathematical
relationship between the
frequency of X-rays and the
atomic number.

26. He noticed that when
struck by the cathode
rays, different metals
gave off x-rays with
distinct wavelengths.

27. Moseley realized that the
atomic numbers were not just a
convenient numbering scheme
for the elements, but had a real
physical meaning - ultimately
realized as being the
number of protons
(and electrons) in an (neutral) element

28. Law of Octaves (1837-1898),
English chemist John Newlands
having arranged the 62 known
elements in order of increasing atomic
masses, noted that at
in intervals of eight, elements had
similar physical/chemical properties.

29. Newlands was the first to
formulate the concept of
periodicity in the properties of the
chemical elements.
In 1863 he wrote a paper
proposing The Law of Octaves:
Elements exhibit similar behavior
to the eighth element following it
in the table.

30. Noble Gases
1864 He discovered on the Sun
1894 Englishman John Williams Strutt
(Lord Rayleigh) and Scottish Sir
William Ramsey discovered Argon
1895 He discovered on Earth
1898 Krypton and Xenon-Ramsey
1900 Radon discovered by
German Friedrich Ernst Dorn