Chemical Bonding: The Ionic Bond Model

Chemical Bonds Forces that hold atoms to each other within a molecule or compound

Ionic Bonds Attractive force holding oppositely charged ions together Ions can be monoatomic or polyatomic Involve “+” charged metal ion (or NH 4 + ) and “–” charged non-metal ion Results in formation of an ionic compound

Covalent Bonds Attractive force between a non-metal and a non-metal Involves sharing of electrons Results in formation of a covalent compound (a true molecule) Covered in Chapter 5

Formation of an ionic bond (and therefore an ionic compound) Transfer of an electron from metal to non-metal (metal loses an electron that the non-metal gains) This creates oppositely charged ions (a metal cation and a non-metal anion) The oppositely charged ions attract (ionic bond) forming an ionic compound (not a discreet molecule)

Ionic compounds exist in a 3D array called a crystal lattice

Since ionic compounds are in a crystal lattice array, they are not discreet molecules Ionic compound formula is always an empirical formula (ie NaCl)

Chemical bonding involves: Losing and gaining of electrons (ionic bonding) Sharing of electrons (covalent bonding) Which shell would have electrons most available to be lost, gained or shared??

Valence shell electrons The outer shell electrons (This is where the action is!!) Valence shell electrons are lost, gained or shared How many are lost, gained or shared? Enough to make the atom stable (like a Noble gas) In other words, enough to have a full outer shell

Lewis structures: representing valence shell electrons

Octet rule To become chemically stable, atoms gain, lose or share however many electrons they need to in order to have a full valence shell Since most outer shells have 8 representative electrons, the term “octet” is used The first shell is an exception because it holds only 2 electrons when full

Prediction ionic charge for Groups IA, IIA, IIIA, VA, VIA, and VIIA Ion Charge

Isoelectronic atoms Atoms of different elements that have the same number of electrons Examples: N 3- O 2- F - Ne Na + Mg 2+

Predicting the formula of an ionic compound Remember: it will always be an empirical formula Criss-Cross Method Na 1+ Cl 1- Ca 2+ Br 1- Mg 2+ O 2- NaCl CaBr 2 Mg 2 O 2 MgO

Naming ionic compounds