5.2 Ionic bonding and structure
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What is ionic bonding
The electrostatic attraction between positive and negative electrons It holds together cations and anions in ionic compounds Each ion attracts oppositely charged ions in ALL directions
Common cations:
metal ions: eg. Na+, Ca2+, Al3+ ammonium ions: NH4+
Common anions
non-metal ions: eg. Cl-, O2- polyatomic ions: NO3-, SO42-
What type of compounds form
Ionic compounds Form a giant ionic lattice structure
What state are most ionic compounds at room temperature
solids
Why are most ionic compounds solids at room temperature
There is insufficient energy to overcome the strong electrostatic forces of attraction between the oppositely charged ions in the giant ionic lattice
Melting and boiling points of ionic compounds
Most have a high melting and boiling point
Which lattices have higher melting points
Lattices which contain ions with greater ionic charges as there is stronger attraction between ions Can also depend on size of ions
Are ionic compounds soluble
Many dissolve in polar solvents such as water
How do ionic compounds dissolve
Polar molecules break down the lattice and surround each ion in solution
Why are some ionic compounds less soluble than other ionic compounds
In compounds made of ions with large charges, the ionic attraction may be too strong for water to be able to break down the lattice structure
Solubility requires two main processes:
The ionic lattice must be broken down Water molecules must attract and surround the ions
Can ionic compounds conduct electricity
Only when molten or dissolved Does NOT when in solid state
Ionic compounds and conducting electricity when solid
DOES NOT HAPPEN The ions are in a fixed position in the giant ionic lattice There are no mobile charge carriers An ionic compound is a non-conductor of electricity in the solid state
Ionic compounds and conducting electricity when liquid (molten) or dissolved in water
The solid ionic lattice breaks down The ions are now free to move as mobile charge carriers An ionic compounds is a conductor of electricity in liquid and aqueous states
Properties of most ionic compounds
Have high melting and boiling points Tend to dissolve in polar solvents such as water Conduct electricity only in the liquid or aqueous states