History of the Periodic
Table
Chapter 5
Chapter 5
History of the Periodic TableThe Periodic LawThe Periodic Law –
Physical and Chemical Properties
of Elements are Periodic Functions
of their Atomic Numbers
History of the Periodic TableThe Periodic LawThe Periodic Law –
Physical and Chemical Properties
of Elements are Periodic Functions
of their Atomic Numbers
The development of the periodic table begins with German chemist
Johann Dobereiner (1780-1849) who
grouped elements based on similarities.
Calcium (atomic mass 40), strontium (atomic mass 88),
and barium (atomic mass 137) possess similar chemical
properties. (Find them on the
Periodic Table)
Dobereiner noticed the atomic mass of strontium fell midway between the masses
of calcium and barium: Ca Sr Ba
40 ?? 137(40 + 137) ÷ 2 = ??
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
(Was this merely a coincidence or did some pattern to the arrangement of the
elements exist?)
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.
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.
(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.)
First International First International Congress of ChemistsCongress of Chemists
Karlsruhe, GermanyKarlsruhe, Germany 1860 1860-to discuss uniform ways to
measure Atomic Mass and to solve other communication
problems.-Only 60 Elements at this timeOnly 60 Elements at this time
First International First International Congress of ChemistsCongress of Chemists
Karlsruhe, GermanyKarlsruhe, Germany 18601860-to discuss uniform ways to
measure Atomic Mass and to solve other communication
problems.-Only 60 Elements at this timeOnly 60 Elements at this time
Mendeleev insisted on ordering elements by
atomic mass, and grouping them by their
PROPERTIES.PROPERTIES.
Demetri Mendeleev 1869 Demetri Mendeleev 1869 FATHER OF THE FATHER OF THE
MODERN PERIODIC TABLEMODERN PERIODIC TABLE
Mendeleev insisted on ordering elements by
atomic mass, and grouping them by their
PROPERTIES.PROPERTIES.
Demetri Mendeleev 1869 Demetri Mendeleev 1869 FATHER OF THE FATHER OF THE
MODERN PERIODIC TABLEMODERN PERIODIC TABLE
Mendeleev insisted on ordering elements by
atomic mass, and grouping them by their
PROPERTIES.PROPERTIES.
Demetri Mendeleev 1869 Demetri Mendeleev 1869 FATHER OF THE FATHER OF THE
MODERN PERIODIC TABLEMODERN PERIODIC TABLE
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)
Mendeleev concluded Mendeleev concluded therefore that there therefore that there must be two elements, must be two elements,
which he called which he called "eka-Aluminum" and "eka-Aluminum" and "eka-Silicon" which "eka-Silicon" which must fill these gaps must fill these gaps
Mendeleev made predictionspredictions on some of the vacant spaces
in the Periodic Table. Such as:
Eka-silicon, (Germainium) Eka-aluminium, (Gallium)
Gallium was discovered in 1875
by Paul Emile. Its general
chemistry matched Mendeleev's
predictions for Eka-aluminium.
72.32
5.5
13
Outer Shell Electrons (Dots)
Property Ekasilicon Germanium
Atomic Mass 72
Density (g/cc) 5.47
Atomic volume 13.22
44
Boiling point of GeCl4
/degrees Celsius86<100
Germanium (ekasilicon) was discovered in 1886 by Clemens Winkler.
The agreement with Mendeleev's predictions are shown in the table below
Henry Moseley 1913Assistant to Rutherford
(killed at Gallipoli at age 28) -discovered a mathematical
relationship between the frequency of X-rays and the
atomic number.
Henry Moseley 1913Assistant to Rutherford
(killed at Gallipoli at age 28) -discovered a mathematical
relationship between the frequency of X-rays and the
atomic number.
He noticed that when struck by the cathode rays, different metals gave off x-rays with
distinct wavelengths.
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
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.
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.
Noble GasesNoble Gases1864 HeHe discovered on the Sun1894 Englishman John Williams Strutt (Lord Rayleigh) and Scottish Sir William Ramsey discovered Argon1895 HeHe discovered on Earth1898 Krypton and Xenon-Ramsey1900 Radon discovered by German Friedrich Ernst Dorn