Chemical Bonding: The Ionic Bond Model
Dec 22, 2015
Ionic BondsIonic Bonds
Attractive force holding oppositely charged ions together
Ions can be monoatomic or polyatomic
Involve “+” charged metal ion (or NH4+) 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)
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
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
Isoelectronic atoms
Atoms of different elements that have the same number of electrons
Examples:
N3- O2- F- Ne Na+ Mg2+
Predicting the formula of an ionic compound
Remember: it will always be an empirical formula
Criss-Cross Method
Na1+ Cl1- Ca2+ Br1- Mg2+ O2-
NaCl CaBr2 Mg2O2
MgO