THE PERIODIC TABLEChapter 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