1. The Periodic Table
Chapter 19
Section 3

2. Organizing the Elements
In the late 1800s, Dmitri Mendeleev searched for a way to organize the elements
His first arrangement was done by increasing atomic masses
Found a pattern
Chemical properties in lighter elements were repeating in heavier elements
The pattern was Periodic
The arrangement is now known as the periodic table
Mendeleev’s table was so well constructed that he was able to predict the location of elements that had not yet been discovered.

3. Improving the Periodic Table
Mendeleev’s table was arranged by atomic mass
But there were some spots were atomic mass placement and atomic properties didn’t make sense
Cobalt and Nickel
In 1913, Henry Moseley proposed a table arranged by increasing atomic number
This change corrected the problems found in Mendeleev’s table
Moseley’s arrangement is the one used in the modern table of elements

4. The Atom and the Periodic Table
The vertical columns of the periodic table are known as groups
The atoms of elements found in the same family have similar properties
This is due to the number of electrons in the outer energy level

5. Electron Cloud Structure
Electrons in the electron cloud have different energies
The differences are modeled by placing them in energy levels.
Low energy Close to the nucleus
High energy Further away from the nucleus
Labeled from 1 to 7
Energy level 1 can hold up to two electrons
Energy level 2 can hold up to 8 electron
Energy level 3 can hold up to 18 electrons
A complete and stable outer energy level will have 8 electrons
Sooo…elements in the same column have the same number of electrons in the outer energy level

6. Rows on the Table
As you go across the table, an electron is added to the outer shell and one proton is added to the nucleus
The row tells you with energy level the outer most electrons are located in
The rows are called periods

7. Electron Dot Diagrams
Electron dot diagrams were introduced by G.N Lewis
They are a short hand way of showing how many electrons are in the outer energy level
They are also used to show how atoms combine to form compounds
Electron dot diagrams will be the same for all elements in a column

8. Regions on the Periodic Table