|
Ionic Bonding [print-friendly version]
Usually
between a metal and a non-metal or a group of non-metals (exception ammonium
compounds which have the NH 4+
positive ion instead of a positive metal ion) e.g. NaCl,CaCl2, PbSO4, CaO, NH4NO3,
Ca(NO3)2 .
- The
positively charged ions and the negatively charged ions are arranged
in a regular 3-D lattice. Each positive ion is surrounded by a fixed
number of negative ions and each negative ion is surrounded by a fixed
number of positive ions.
- In
ionic solids, ions occupy fixed positions in the regular
lattice.
- The
overall charge is zero.
- The
strong electrical attraction between the positive and negative ions
is called IONIC BONDING.
- The formula represents the
ratio of positive ions to negative ions e.g. NaCl means ratios of Na+
ions to Cl- ions = 1:1 ; CaCl2 means the
ratio of Ca2+: Cl- = 1:2
- The
ionic bonding explains the physical properties.
|
Property
|
Explanation
|
|
Non-conductor
(solid)
|
Ions
are in a fixed lattice - no mobile charged particles available
to carry charge.
|
|
Good
conductor (Molten
or in aqueous solution)
|
Ions
are now mobile; and both positive and negative ions can carry the
charge.
|
|
High melting
point and boiling point.
|
The strong ionic
bonding extending throughout the lattice (due to the strong electrostatic
attractions between the positive and negative ions) means that a
large amount of thermal energy is needed to overcome these forces
- hence high melting point.
|
|
Hard
|
Strong ionic
bonding extends throughout the lattice. Scratching requires overcoming
this strong ionic bonding.
|
|
Brittle
|
The
ionic lattice does not withstand distortion - when the lattice is
distorted like charged ions come into contact and repel one another
- the lattice shatters.
|
|
