The document discusses the development of the periodic table. It describes how Mendeleev arranged elements in order of increasing atomic mass and noticed periodic trends in their properties. Later, Moseley arranged elements by atomic number, establishing it as the fundamental property for ordering elements. The periodic table is now organized into rows and columns, with columns of elements having similar properties called groups.

1. The Modern Periodic Table
Chapter 5
The
History

2. Chapter 5 – The Periodic Law
 60
By 1860, over ____ elements had been
discovered.
 atomic
Scientists were using different _______
masses
________ for the elements.
 They got together and decided on the
average atomic masses
________ ________ _________.

3. Dmitri Mendeleev and Periodicity
 Noticed that when elements were arranged in
order of ___________ ________ _______,
increasing atomic mass
properties
certain similarities in ___________ occurred
at regular intervals.
 Such a repeating pattern is referred to as
periodicity
___________.
 He created the first periodic table based on
atomic masses
________ __________.

4. The first published periodic table by
Mendeleev

5. Henry Mosely and the Periodic Law
 In 1911, he was working with ____________.
Rutherford
 He noticed a pattern when elements were
arranged in increasing nuclear _________
charge
(# of ________).
protons
 This work lead to the modern definition of
atomic number
________ _________.
 The periodic table is now arranged according
atomic number
to ________ _________.

6. Periods of the Periodic Table
 ________ across the periodic table
Rows
 7
There are ____ periods.

7. Groups of the periodic table
 families
also called ___________
 the _________ (up & down) of the periodic
columns
table.
 elements of the same group have similar
_________.
properties
 18
There are ___ groups
 Groups 1, 2, 13, 14, 15, 16, 17, 18 also
1A, 2A, 3A, 4A, 5A, 6A, 7A, 8A
called: ______________________________