The document summarizes the development of the modern periodic table by key scientists from the 19th and 20th centuries. Johann Dobereiner first classified elements into triads in 1817 based on similarities in properties. John Newlands proposed the Law of Octaves in 1869, arranging elements by atomic mass. Dmitri Mendeleev published the first recognizable periodic table in 1869, arranging elements by atomic mass and leaving spaces for undiscovered elements. His predictions based on the table were later verified. Moseley determined atomic number to be the fundamental property in 1913. Seaborg moved elements below the lanthanides in 1944 to form the actinide series. The modern periodic table arranges elements by increasing atomic number and

1. The History
of the
Modern
Periodic
Table and its

2. How did the Periodic Table
develop?
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.

3. Who were the persons
involved in the
development of periodic
table?

4. Johann Dobereiner
1780 - 1849
Model of triads
In 1817, 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)

5. John Newlands
1838 - 1898
Law of Octaves
In 1869, 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.

6. John Newlands
1838 - 1898 Law of Octaves
Newlands' claim to see a repeating pattern
was met with savage ridicule on its
announcement. His classification of the
elements, he was told, was as arbitrary as
putting them in alphabetical order and his
paper was rejected for publication by the
Chemical Society.

7. Dmitri Mendeleev
1834 - 1907
In 1869 he published a
table of the elements
organized by increasing
atomic mass.

8. Mendeleev’s Periodic Table

9. Lothar Meyer
1830 - 1895
At the same time, he published his
own table of the elements
organized by increasing atomic
mass.

10. • Both Mendeleev and Meyer
arranged the elements in order of
increasing atomic mass.
• Both left vacant spaces where
unknown elements should fit.
So why is Mendeleev called the
“father of the modern periodic
table” and not Meyer, or both?

11. • stated that if the atomic weight of
an element caused it to be placed
in the wrong group, then the
weight must be wrong. (He
corrected the atomic masses of
Be, In, and U)
• was so confident in his table that
he used it to predict the physical
properties of three elements that
were yet unknown.
Mendeleev...

12. After the discovery of these
unknown elements between 1874
and 1885, and the fact that
Mendeleev’s predictions for Sc, Ga,
and Ge were amazingly close to the
actual values, his table was
generally accepted.

13. Henry Moseley
1887 - 1915
In 1913, through his work with X-
rays, he determined the actual
nuclear charge (atomic number) of
the elements*. He rearranged the
elements in order of increasing
atomic number.*“There is in the atom a
fundamental quantity which
increases by regular steps as we
pass from each element to the
next. This quantity can only be
the charge on the central positive
nucleus.”

14. Henry Moseley
His research was halted when the
British government sent him to serve as a
foot soldier in WWI. He was killed in the
fighting in Gallipoli by a sniper’s bullet, at
the age of 28. Because of his loss, the
British government later restricted its
scientists to noncombatant duties during
WWII.

15. Glenn T. SeaborgAfter co-discovering 10 new
elements, in 1944 he moved 14
elements out of the main body of
the periodic table to their current
location below the Lanthanide
series. These became known
as the Actinide series.
1912 - 1999

16. Glenn T. Seaborg
He is the only person to have an
element named after him while still
alive.
1912 - 1999
"This is the greatest honor ever
bestowed upon me - even better, I
think, than
winning the Nobel Prize."

19. Periodic Table
were arranged according to
increasing atomic number

20. Arrangement of Elements
in the Periodic Table
The P.T. organizes
elements in such a way
that chemical and physical
information about the
elements and their
compounds are easily
revealed.

21. What is atomic number?
• the no. of protons in the nucleus of
an atom, which determines the
chemical properties of an element
and its place in the periodic table.

22. Family or Group-
GROUP 1-18
vertical column of the periodic table.

23. The vertical columns of the periodic table
are called GROUPS, or FAMILIES.
The elements in any group
of the periodic table have
similar physical and chemical
properties!

24. Period or Series-
PERIOD 1-7
horizontal row and numbered from
the top to down.

25. The horizontal rows of the periodic table
are called PERIODS OR SERIES.

26. Alkali Metals

27. Alkaline Earth Metals

28. Transition Metals

29. InnerTransition Metals
These elements are also
called the rare-earth
elements.

30. Halogens

31. Noble Gases

32. The periodic table is the most
important tool in the chemist’s
toolbox!

33. SHORT QUIZ:Complete the table
ELEMENT SYMBOL ATOMIC
NO.
GROUP PERIOD
Magnesium
Arsenic
Cobalt
Argon
Germanium
Gold
Boron
Phosphorous
Francium

34. ..thanks for
Listening…