JOURNAL #43
Who
is Niels Bohr?
What was his contribution to
chemistry?
What do you already know
about the periodic table of
elements?
THE PERIODIC LAW
MENDELEEV
 Russian
Chemist
 He observed that when elements are
arranged in order of increasing atomic
mass, certain similarities in their
chemical properties appeared at regular
intervals.
 Such repeating pattern is referred to as
periodic.
 Mendeleev’s principle was not widely
accepted (as there were only 60 known
elements, leaving gaps in the table)
MOSELEY
 The
elements in the periodic table fit into
patterns better when arranged in
increasing order according to nuclear
charge, or number of protons in the
nucleus.
 Now, Mendeleev’s principle is correctly
stated in what is known as the periodic
law:

The physical and chemical properties of the
elements are periodic functions of their
atomic numbers.
THE MODERN PERIODIC TABLE
 The
periodic table has undergone
extensive changes since Mendeleev’s time.
 Chemists have discovered new elements,
and synthesized new ones in the lab.
 The periodic table is an arrangement of
the elements in order of their atomic
numbers so that elements with similar
properties fall in the same column or
group.
THE MODERN PERIODIC TABLE
 The
noble gases, also known as group 18
elements, are all rather unreactive.
 The lanthanides- are the 14 elements with
atomic numbers from 58 Ce to 71 Lu.
 The actinides- are the 14 elements with
atomic numbers from 90 Th to 103 Lr
LET’S REVIEW:
 Who
discovered the Periodic Law?
Answer: Mendeleev
 Who
established atomic numbers as the
basis for organizing the periodic table?
Answer: Moseley
DESIGN YOUR OWN PERIODIC TABLE
Can you design your own periodic table using
information similar to that available to
Mendeleev?
 Organize the cards for the elements in a logical
pattern as you think Mendeleev might have done.
 Answer the following:






Why are atomic masses given instead of atomic
numbers?
Can you identify each element by name?
How many groups are in your periodic table?
How many periods are in your table?
Predict the characteristics of missing elements.