1.4 Properties Flashcards
What is an Ionic Compound?
lonic compounds form what is known as a lattice structure. This is a
regular arrangement of metal and non-metal ions.
A lattice structure creates compounds with a high melting point which
conduct when molten or in solution but NEVER when solid.
lonic compounds dissolve in water easily. When they do this their lattice
breaks up completely to form free ions. This enables them to conduct
electricity as the ions are free to carry the electrical charge. They also have a
high melting point because to melt an ionic compound the millions upon
millions of strong ionic bonds must be broken and this requires lots of energy.
Not all ionic compounds form cube-like structures and a variety of shapes
can be created from ionic crystals.
What is a covalent network?
Covalent network substances have very high melting points and are
very hard. Diamond for example is a covalent network structure made of
carbon atoms and is used in cutting tools for cutting through rock.
The many carbon atoms are held together by strong covalent bonds
which give diamond the properties of being very hard as well as having a
very high melting point.
What is a covalent molecular?
Covalent molecules such as oxygen and water all have low melting
points and boiling points. This means that they are a liquid, gas or low
melting point solid at room temperature. Like all covalent compounds
they do not conduct electricity in any state, water being the only
exception to this rule.
When a substance such as ice is melted, it is only the weak bonds
between the molecules and not the strong covalent bonds that are
broken.
There are always exceptions to these rules of bonding such as:
• Graphite is a covalent network of carbon atoms that does conduct
electricity due to the fact that it has delocalised (free to move)
electrons.
• Titanium tetrachloride (TiCl4,) is a compound with low melting and
boiling points. This is because it is a covalent molecular substance even
though it contains a metal.
The ‘remember’ boxes show two ways of summarising this information
about the properties of substances with different types of bonding. Use
whichever one suits you best or even a mixture of both.
What is the MP and BP of an ionic lattice?
High.
What is the MP and BP of covalent networks?
Very high.
What is the MP and BP of covalent moleculars?
Low.
What form is an ionic lattice at room temperature?
Solid.
What is the form of a covalent network at room temperature?
Solid.
What is the form of a covalent molecular at room temperature?
Liquid, gas or LOW melting point solid.
When does an ionic lattice conduct electricity?
Only when MOLTEN or in SOLUTION.
When does a covalent network conduct electricity?
Never (except graphite)
When does a covalent molecular conduct electricity?
Never.
