Download Ionic Bonding

Ionic Bonding
Ionic Bond
 Chemical
bond resulting from
electrostatic attraction between
positive and negative ions.
– Goal: achieve stable octet of electrons
(noble gas configuration)
 Illustrate
by
– Orbital notation
– Lewis Dot diagrams
Show transfer of VALENCE electrons to achieve octet
But WHICH electrons (i.e. what orbitals) are involved?
Formation of
The Octets
A quantum mechanical representation of the electron transfer
Three Types of Bonding
 Ionic
– electrons are transferred.
 Covalent
–
electrons are shared.
 Metallic
–
“sea of mobile electrons.”
Identify Bond Type from Formula
 Ionic
Compounds
– metal + nonmetal
 Covalent
Compounds
– nonmetal + nonmetal
 Metallic
– metal symbol
Na metal 
Metals lose e-
Nonmetals gain e-
Cl2 (g) 
Ionic Compounds



Composed of positive and negative ions
combined so that compound is NEUTRAL.
Most ionic compounds are …
crystalline solids.
Expressed as Formula Units, not
molecules (which are covalent)!
– Simplest ratio of atoms (empirical formula)
Structure of Ionic Compounds


Ions are attracted to each other by strong
electrostatic interactions.
Form a crystal lattice
– a regular 3-D pattern or array.
– Ions are held in fixed positions in the solid state.

Unit Cell = smallest repetitive unit in lattice
Strength of Ionic Bond

Lattice Energy
– Energy released
when one mole of
an ionic crystalline
compound is
formed from
gaseous ions.
Na+(g) + Cl−(g) → NaCl
The experimental lattice energy of NaCl is −787 kJ/mol.
Shown as negative value  Exothermic
Electron is transferred from Na to Cl
Tiger Graphic
Oxidation Number
Determines how many atoms are needed to form the ionic compound.
Properties of Ionic Compounds
 High
melting points
 Low vapor pressures
 Solids do not conduct electricity
 Melts (liquids) do conduct electricity
 Solutions (aq) conduct electricity
– electrolytes:
 Tend
substances whose water solution
conducts an electric current.
to be hard and brittle
 High solubility in water.
Aside: What Conducts Electricity?
***MOBILE CHARGED PARTICLES***


If something conducts a current, it has
some kind of mobile charged particles:
either electrons (solids) or ions (solutions).
If something doesn’t conduct, it doesn’t
have particles that are both mobile and
charged.
Linus Pauling
 1954
Nobel Prize Chemistry
 First
to show that chemical
bonds could show degrees of
both a covalent and ionic
nature.
 Led
to the development of
electronegativity values.
Electronegativity Difference
1.7
Electronegavitity Difference



Bonding between atoms is a continuum
from ionic to covalent.
The larger the difference in
electronegativity between two bonded
elements, the more ionic in character the
bond has.
Which has more ionic character?
– CaO or KF or LiH
Bonding Character