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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.
Dmitri Mendeleev
In 1869 he published a table of
the elements organized by
increasing atomic mass.
1834 - 1907
• stated that if the atomic mass 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.
Henry Moseley
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.”
1887 - 1915
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 this loss, the
British government later restricted its
scientists to noncombatant duties during
Periodic Table
The horizontal rows of the periodic table
are called PERIODS.
The elements in any group
of the periodic table have
similar physical and chemical
The vertical columns of the periodic table
are called GROUPS, or FAMILIES.
Periodic Law
When elements are arranged in order of
increasing atomic number, there is a
periodic pattern in their physical and
chemical properties.
Alkali Metals
Alkaline Earth Metals
Transition Metals
These elements are also
called the rare-earth
InnerTransition Metals
Noble Gases
The s and p block elements
are called
The periodic table is the most important
tool in the chemist’s toolbox!
Atomic radii
• Atomic size gradually decreases from left to
right across a period of elements
• Going down a group, it can be seen that
atomic radius increases
left to
right radius
across a
a group,decreases
it can be from
seen that
of elements
Periodic Trends for
• Electronegativity measures an atom's strength
to attract and form bonds with electrons.
As you
you move
move down
to thearight
across a period of
elements, electronegativity
decreases. increases.