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What Does Periodic Mean?
The properties of the elements are periodic
functions of their atomic numbers.
Huh?
As atomic number increases, certain properties
of atoms repeat periodically
PeriodicallyAt regular intervals
Unit 5: The
Periodic Table
Lesson 5.1:
The
Development
of the Periodic
Table.
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The History of the
Modern
Periodic Table
During the nineteenth century,
chemists began to categorize the
elements according to similarities in
their physical and chemical properties.
The end result of these studies was our
modern periodic table.
Antoine Lavoisier
Johann Dobereiner
• Early classification of elements
– First person to attempt to sort elements
into groups
– First periodic table, which contained 33
elements
– Periodic table based on chemical properties
– Some of these were later found to be
compounds
– The table did show a distinction between
metals and non-metals
In 1829, he classified some elements into groups of
three, which he called triads.
The elements in a triad had similar chemical
properties and orderly physical properties.
(ex. Cl, Br, I and
Ca, Sr, Ba)
Model of triads
1780 - 1849
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William Odling
John Newlands
• 1864 - Classification of elements into two
dimensions
– Found a horizontal connection between
the elements fluorine, oxygen, nitrogen
and carbon (first element in groups 1 – 4)
– Overcame problems that
mandeleev has on 1st attempt
– Did not get credit for all his work
In 1863, he suggested that elements be
arranged in “octaves” because he noticed (after
arranging the elements in order of increasing
atomic mass) that certain properties repeated
every 8th element. – Not true past Ca
Law of Octaves
1838 - 1898
(1829-1921)
Dmitri Mendeleev
Lothar Meyer
 A German chemist,
 Worked on classification of the
elements.
 His periodic law, stated that the
properties of the elements are
periodic functions of their
atomic weights.
 Was late to publish – did not get
1830 - 1895
credit
• In 1869 he published a table of the
elements organized by increasing
atomic mass.
• Received more credit than Mayer
He left spaces in his table for
as yet undiscovered
elements, and predicted
properties of those
elements.
1834 - 1907
Henry Moseley
– Though a good model, Mendeleev could
not explain inconsistencies, for instance, all
elements were not in order according to
atomic mass
– 1913 - Henry Moseley explained the
discrepancy
– Discovered correlation between number
of protons (atomic number) and
frequency of X rays generated
– Today, elements are arranged in order
of increasing ATOMIC NUMBER
The Modern Periodic Law
Henry Moseley
(1887 – 1915)
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• This is the basis for the modern
Periodic Table
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Periodic Table by Dates of Discovery
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