2 MendeleevDmitri Mendeleev first organized elements according to atomic mass.He noticed similarities in their chemical properties appeared at regular intervalsSuch a pattern is called periodicThing to remember: its just a general trend
4 Periodic Law Mendeleev’s table has gaps! Two questions he posed: 1. Why could most elements be arranged in order of increasing atomic mass, but some couldn’t?2. What is the reason for chemical periodicity?
5 Periodic LawMoseley, who worked with Rutherford, discovered that atomic number, not atomic mass, is the basis of organization. This led to…Periodic Law: The physical and chemical properties of the elements are periodic functions of their atomic numbers.
6 Periodic Table Organization Vertical columns in the periodic table are known as groups or families
7 Periodic Table Organization Horizontal Rows in the periodic table are known as Periods