1. The Periodic Law History of the Periodic Table

2.  Objectives  Explain the roles of Mendeleev and Moseley in the development of the periodic table  Describe the modern periodic table  Explain how the periodic law can be used to predict the physical and chemical properties of elements  Describe how the elements belonging to a group of the periodic table are interrelated in terms of atomic number

3. History of the Periodic Table  Mendeleev and Chemical Periodicity  Mendeleev noticed that when the elements were arranged in order of increasing atomic mass, certain similarities in their chemical properties appeared at regular intervals  Repeating patterns are referred to as periodic  Mendeleev created a table in which elements with similar properties were grouped together—a periodic table of the elements

4. History of the Periodic Table  Mendeleev and Chemical Periodicity  After Mendeleev placed all the known elements in his periodic table, several empty spaces were left  In 1871 Mendeleev predicted the existence and properties of elements that would fill three of the spaces  By 1886, all three of these elements had been discovered

5. History of the Periodic Table  Three Elements Predicted By Mendeleev

6. History of the Periodic Table  Moseley and the Periodic Law  In 1911, the English scientist Henry Moseley discovered that the elements fit into patterns better when they were arranged according to atomic number, rather than atomic weight  The Periodic Law states that the physical and chemical properties of the elements are periodic functions of their atomic numbers

7. History of the Periodic Table  Periodicity of Atomic Numbers

8. History of the Periodic Table  The Modern Periodic Table  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

9. History of the Periodic Table  The Modern Periodic Table