1. Periodic Table History
From Dobereiner to the Present

2. J.W. Dobereiner Early 1800s, German
Elements classified into groups of 3: triads
Elements in triad have similar properties
Properties of middle element are average of the first and third elements in triad

3. J.A.R. Newlands
1800s, British
Elements arranged in order of increasing atomic mass – pattern repeats every 8 elements
Law of octaves

4. Dmitri Mendeleev Russian, 1800s; Lothar Meyer developed concurrently
Organized elements by increasing atomic mass
Elements with similar properties grouped together
Had some discrepancies, but predicted properties of undiscovered elements

5. Henry Moseley Early 20th century, British
Organized elements by atomic number
This solved discrepancies in Mendeleev’s periodic table

6. Groups Vertical columns in table
Elements in a group have similar chemical properties

7. Periods Horizontal rows in table are called periods
Represent energy level or principal quantum number, n

8. Organization of Elements in Modern Periodic Table
Metallic Character
Metals
Nonmetals
Metalloids

9. Organization (Continued)
Blocks
Main Group Elements
Transition Metals
Inner Transition Metals

10. Numbering
IUPAC and American Numbering Systems