THE PERIODIC TABLE
Chapter 19
Section 3
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.
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
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
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
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
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
Regions on the Periodic Table