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

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

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

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

Write the electron dot diagram for Na Mg C O F Ne He

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

Electron Dot Structures Symbols of atoms with dots to represent the valence-shell electrons 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 :        

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

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

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

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

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

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.

Ionic Bonding Na Cl

Ionic Bonding Na+ Cl-

Lewis Structures Ionic – show transfer of e-

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

Ionic Bonding Ca P

Ionic Bonding Ca2+ P

Ionic Bonding Ca2+ P Ca

Ionic Bonding Ca2+ P3- Ca

Ionic Bonding Ca2+ P3- Ca P

Ionic Bonding Ca+2 P3- Ca2+ P

Ionic Bonding Ca Ca2+ P3- Ca2+ P

Ionic Bonding Ca Ca2+ P3- Ca2+ P

Ionic Bonding Ca2+ Ca2+ P3- Ca2+ P3-

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