Ch. 6 Chemical Bonding A Chemical Bond occurs when valence electrons are lost, gained, transferred or shared between two or more atoms.

The Octet Rule Atoms tend to gain, lose, or share electrons until they have eight valence electrons. This is called a “Stable Octet.”

Why Do Atoms form a Bond? To form a state of lower potential energy. Bonded atoms require less energy To become more stable. A Stable Octet of 8 electrons resembles the Nobel Gases.

The Three types of Bonds Ionic Bond – Transfer of electrons from a cation to an anion.

The Three types of Bonds Covalent Bond Sharing of electrons so that all atoms involved maintain a Stable octet.

Three types of Bonds Metallic Bond Cations attracted to other Cations by a sea of electrons surrounding all of the positive ions. Sea of electrons

Identifying the Bond When Metals bond to Non-Metals they will form an Ionic Bond When Non-Metals bond to other Non-Metals they will form a Covalent Bond When Metals bond to other Metals they will form a Metallic Bond

Lewis Dot Diagrams Lewis symbols show the valence electrons as dots arranged around the atomic symbol. hydrogen: sodium: chlorine: H · Na · Cl · · ·

Using Lewis Dot Diagrams for Ionic compounds and Covalent molecules Formation of sodium chloride: Cl · · · ® Na+ [ ] Cl · · Na · + Formation of hydrogen chloride: Cl · · · ® Cl · · H H · + When filling up valence shells make sure all non-metals finish with a stable octet. If possible all elements should finish with an octet.

Ex. NaCl and MgO not “ClNa” or “OMG” Basic Formula Writing When writing a formula the most metallic element is written first.(leftmost on the P.table) Ex. NaCl and MgO not “ClNa” or “OMG” Subscripts are to be used to represent the number of elements or ions needed to make all species maintain a octet. Ex. H2O or AlBr3 (A subscript of 1 is understood and is not written.)

Bond Determination H + F Ca + Cl Al + O * Cu + N K + P N + Br As + S Using e-dot diagrams determine the formulas for the following. Metal to Non-Metal  Ionic Non-Metal to Non-Metal  Covalent H + F Ca + Cl Al + O * Cu + N K + P N + Br As + S Ionic Covalent HF CaCl2 Al2O3 Cu3N or Cu3N2 K3P NBr3 As2S3 When writing the formula of a compound or molecule the more metallic element is always written 1st ( furthest to the left)

Determining Formulas The Criss-Cross Method A short cut to formula writing can be accomplished using the oxidation or charge of ions to determine the chemical formulas of compounds. Examples Na+1 + O-2  Ca+2 + P-3  C+4 + O-2  Na2O Ca3P2 C2O4  reduced to CO2