.

 Valence Electrons ◦ Electrons in highest energy level ◦ Largely responsible for chemical behavior (properties, bonding)  Noble gases have eight valence electrons. They are unreactive…meaning they don’t form bonds or compounds.  Eight valence electrons is important in the stability of atoms.

 Octet Rule: atoms tend to gain, lose, or share electrons in order to acquire a full set of 8 valence electrons.  All atoms want to have eight valence electrons…to be stable.

 How does a positive ion form?  Positive ions are formed by losing electrons. Atoms lose as few electrons as possible in order to achieve noble gas configuration or the octet rule.  Remember, low ionization energy is best for losing electrons. Where are the elements that are most likely to lose electrons?  On the left side…metals! Metals form + ions.

 A positive ion is called a cation.  Consider stability. Which is more stable: a neutral Na atom or a Na + ion? Hint: Which has an electron configuration or a number of valence electrons closer to the noble gases?  The sodium ion is more stable.

 Remember, electronegativity involves attracting electrons, and a negative ion is formed by gaining electrons.  A high electronegativity is helpful in forming a negative ion. Where are elements found that are most likely to gain an electron forming a negative ion?  On the right side of the table…nonmetals! Nonmetals form –ions.

 What is more stable a neutral chlorine atom or a Cl - ?  The chlorine ion has an electron configuration similar to a noble gas.  SIMPLE: All atoms want an electron configuration like a noble gas. They will gain or lose as few electrons as possible to do so.

 Name of parent element + “ion”  Indicate charge of transition metals in parentheses Mg 2+ magnesium ion Na + sodium ion Cu 2+ copper (II) ion Al 3+ aluminum ion

 Root of parent atom + suffix “-ide” Clchlorine atom Cl - chloride ion Ffluorine atom F - fluoride ion Ooxygen atom O 2- oxide ion

 Chemical bond: force that holds 2 atoms together (holds compounds together)  Valence electrons are involved in the formation of chemical bonds between atoms.

 Opposites _____________________.  Let’s look at a reaction between sodium and chlorine.  Sodium likes to lose electrons to become a cation. Chlorine likes to gain electrons to become an anion.  A bond forms between the ions called an ionic bond.

 Ionic bond: the electrostatic force that holds oppositely charged particles together in an ionic compound  Compounds that contain ionic bonds are called ionic compounds.  Ionic compounds form between metals and nonmetals. Ex.: Na + and Cl - form NaCl

 Formula units give the proportions and identities of atoms that come together to form unit cells of ionic compounds.  Unit cells are order arrangements of ions that minimize repulsive forces.  Coordination number: ion is the number of ions of opposite charge that surround the ion in a crystal.

Unit cells form beautiful crystals… Ionic compounds are crystals!