1. Valence Electrons Electrons in the highest (outer) energy level
known as valence electrons
have most contact with other atoms
responsible for the chemical properties of atoms
Outer s and p shells of noble gases contain 8 valence electrons (except He = 2)
Example: Ne 2, 8
Ar 2, 8, 8

2. Keeping Track of Electrons
Atoms in the same column
Have the same outer electron configuration.
Have the same valence electrons.
valence electrons - easily found from the group number of the representative elements on the periodic table.
Group 2 - Be, Mg, Ca, etc.- have 2 valence electrons

3. X Electron Dot diagrams A way of keeping track of valence electrons.
How to write them
1. Write the symbol
2. Put one dot for each valence electron on each of the four sides of the symbol
3. Pair up only after all four sides of the symbol are occupied by one electron X

4. The Electron Dot diagram for Nitrogen
Nitrogen has 5 valence electrons.
First we write the symbol N
Then add 1 electron at a time to each side
Pair up the 5th electron with the
1st electron

5. Write the electron dot diagram forNa Mg C O F Ne He

6. Learning Check A. X would be the electron dot formula for
A. X would be the electron dot formula for
1) Na 2) K 3) Al
 
B  X  would be the electron dot formula
1) B 2) N 3) P

7. Electron Dot Structures
Symbols of atoms with dots to represent the valence-shell electrons
H He:
          
Li Be  B   C   N   O  : F  :Ne:
       
          
Na Mg  Al  Si  P S :Cl  :Ar :
       

8. Electron Dots For Cations
Metals will have few valence electrons (usually 3 or less) Ca

9. Electron Dots For Cations
Metals will have few valence electrons
These will come off Ca

10. Electron Dots For Cations
Metals will have few valence electrons
These will come off
Forming positive ions
Ca2+
Pseudo-noble gas configuration

11. Electron Dots For Anions
Nonmetals will have many valence electrons (usually 5 or more).
They will gain electrons to fill outer shell. P
P3-

12. Chemical Bonds Attraction between two or more atoms
Interaction between valence electrons
Ionic bonds
Covalent bonds

13. Ionic Bonding
Anions and cations are held together by opposite charges.
Simplest ratio of ions is called the formula unit.
The bond is formed through the transfer of electrons.
Electrons are transferred to achieve noble gas configuration.

14. Ionic Bonding Na Cl

15. Ionic Bonding
Na+
Cl-

16. Lewis Structures
Ionic – show transfer of e-

17. Ionic Bonding
All the electrons must be accounted for! Ca P

18. Ionic Bonding Ca P

19. Ionic Bonding
Ca2+ P

20. Ionic Bonding
Ca2+ P Ca

21. Ionic Bonding
Ca2+
P3- Ca

22. Ionic Bonding
Ca2+
P3- Ca P

23. Ionic Bonding
Ca+2
P3-
Ca2+ P

24. Ionic Bonding Ca
Ca2+
P3-
Ca2+ P

25. Ionic Bonding Ca
Ca2+
P3-
Ca2+ P

26. Ionic Bonding
Ca2+
Ca2+
P3-
Ca2+
P3-

27. Ionic Bonding
Ca3P2
Formula Unit – smallest whole number ratio of ions in an ionic compound