1. Unit 4 - The Periodic Table
Currently there are over 110 elements. They must be organized in order to study them easily
Originally organized by chemical and physical properties.
Chemical Property
Describes how a substance behaves in a chemical reaction
Usually ends up with a different substance
How substance interacts with others

2. I. History of the Periodic Table
A. Johann Dobereiner
1829
Noticed that some elements have similar properties
Created sets of elements called “Triads”
Lightest element was on top, heaviest on bottom Br Cl Li Na I K Br Na I K
While most people assumed this was coincidence, Dobereiner’s work laid the groundwork for future scientists

3. Organized elements by increasing mass
B. John Newlands
1864
Organized elements by increasing mass
Noticed that every 8th element had similar properties
Li Be B C N O F Na Mg
“Law of Octaves”
As new elements were discovered, this theory broke down. But Newlands determined that elements properties were related to their mass
C. Dimitri Mendeleev
1869
Created the first Periodic Table of Elements
Organized elements by increasing mass
Aka Santa Claus!
Similar elements were put in the same column
Left blank spaces in his table for undiscovered elements
Li Be B C N O F
Na Mg Si ?
Accurately predicted the chemical and physical properties of these unknown elements

4. Hmm… I think I can improve this!
D. Henry Moseley
1914
Used x-ray crystallography to improve on
Mendeleev’s table
Organized elements by increasing ATOMIC
NUMBER
Hmm… I think I can improve this!
Basically, the same table as Mendeleev
Created the Modern Periodic Law
“Properties of Elements are periodic functions of their atomic numbers”
When the elements are lined up by atomic number, their properties begin to repeat.

5. II. Organization of the Periodic Table
A. Periods
Period is a horizontal row
1st period =
H, He
2nd period =
Li, Be, … Ne
The Period number tells you how
many principal energy levels are used
Ex. K is in the 4th period, so it has 4 principal energy levels
Lanthanide and Actinide series
F sublevel is being filled
Actually belong in the normal table, but it is cut out to make it shorter

6. C. Groups
Vertical Columns
aka “Family”
Now numbered 1-18
All members of a family
have similar chemical reactivity.