1. And Electron Structure
The Periodic Table
And
Electron Structure

2. Electrons & the Periodic Table
Mendeleev developed his Periodic Table without even knowing that electrons existed.
However, as time went on and scientists came to a better understanding of the structure of atoms, they made a startling discovery.
In organizing the elements into a table based on their properties, they had unwittingly organized the elements according to their electron structures.

3. The Periodic Table is organized according to electron structure.
A web page that shows the order of filling

4. The Periodic Table and Valence Electrons
Even more important, a careful study of the Periodic Table shows the relationship between valence electron structure and location in the Periodic Table.
***valence electrons - the electrons in the outermost energy level of an atom.

5. Electron Dot Diagrams
To help us understand how the Periodic Table organizes the elements according to their valence electrons, we need to learn a new way of representing the electron structure of an atom. This method is called an electron dot diagram (or Lewis diagram).
Electron dot diagrams use dots to represent valence electrons.
The nucleus and the inner electrons (sometimes called the kernel of the atom) are represented by the element’s symbol.

6. Valence electrons for Carbon
The valence electrons are the electrons located in the outermost energy level of an atom. They are the last number in the electron configuration found in the Periodic Table. Carbon has 4 valence electrons.

7. Electron Dot Diagram for Carbon
The symbol for Carbon (C) is used to represent the nucleus of the carbon atom and the two inner electrons.
The electron dot diagram for a Carbon atom
Four dots representing the four valence electrons in a carbon atom are then arranged around the four sides of the symbol
The first two dots are paired.
Remaining dots are not paired.

8. Electron Dot Diagram for Br
The symbol for Bromine (Br) is used to represent the nucleus of the bromine atom and the inner electrons.
The electron dot diagram for a Bromine atom
According to the Periodic table, Bromine has 7 valence electrons. Therefore we will need to place 7 dots around the symbol.
The first two dots are paired.
Remaining dots are arranged around the other 3 sides.

9. Practice and Discovery
Use what you have learned to complete a chart of the first 18 elements containing their electron dot diagrams in your notebooks. 1 2 13 14 15 16 17 18 H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar
Is there a relationship between the Periodic Table and valence electron structure? What is it?

10. Your completed chart
Elements in the same families of the Periodic Table (except for He) have the same number of valence electrons.
Today we know that the valence electrons are responsible for determining the chemical properties of the elements.

11. Self-check
Use the fact that elements in a group or family have the same number of valence electrons to determine the electron dot diagram for the following elements (use X to represent the symbol):
A halogen
An alkali earth metal
A noble gas
An alkali metal

12. Location of Valence electrons
More information
The Periodic Table provides even more information about the electron structure of an atom by indicating in which energy level the valence electrons are located in.
Period #
Location of Valence electrons 1
1st Energy Level 2
2nd Energy Level 3
3rd Energy Level 4
4th Energy Level 5
5th Energy Level 6
6th Energy Level 7
7th Energy Level

13. A quick glance tells a lot
For this reason, by just glancing at the Periodic Table we can tell what the valence shell is and how many electrons it contains.
Try it for:
Sulfur
Iodine
Barium
Lead
Xenon
S 3rd (6 e-)
I 5th (7 e-)
Ba 6th (2 e-)
Pb 6th (4 e-)
Xe 5th (8 e-)

14. Let’s review!
The arrangement of elements in the Periodic Table is related to the electron structure of the element.
Valence electrons are the electrons in the outermost energy level.
Electron dot diagrams use the symbol of the element to represent the kernel of the atom and dots to represent valence electrons.
In general, all elements in the same group have the same number of valence electrons.
Elements of the same Period have their valence electrons in the same energy level.