Structures and properties
You must learn the following:
The Structure and properties of:
• Giant Ionic lattices eg, Sodium chloride
• Simple molecular covalent compounds
• Giant covalent structures eg, diamond
and graphite, Silicon dioxide
Giant ionic lattices, eg sodium chloride
Ions form a regular pattern due to positive and negative
charges attracting
Ionic bonds are strong causing high melting and boiling point
Ionic compounds conduct electricity when molten (or dissolved in
water) because ions are free to move and carry the current
Simple molecular covalent compounds
Properties of simple molecular covalent substances:
• Strong covalent bonds between atoms
• Weak forces between molecules causing low melting and boiling points
• Do not conduct electricity because molecules have no overall electrical
charge
Giant Covalent Structures eg diamond
Each carbon atom in diamond has 4 strong covalent
bonds so is very hard and has a high melting point
and boiling point
Giant covalent structures eg, Graphite
• Each carbon atom bonds to 3 other atoms forming
layers which are free to slide over each other
• Higher tier: one electron from each carbon is
delocalised and is free to move and carry current
Silicon dioxide
Sand is mostly made of the mineral quartz, which is silicon dioxide.
It has a giant covalent structure made up of silicon and oxygen atoms
Each silicon atom (2.8.4) is bonded to four oxygen atoms, and
each oxygen atom (2.6) is bonded to two silicon atoms.
O
Si
O
O
O
Bonding
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© Boardworks Ltd 2007
Bonding summary
The properties of polymers depend on what they
are made from and the conditions they are made
For example, low density (LD) and high density (HD)
poly(ethene) are produced using different catalysts
and reaction conditions
Thermo softening polymers consist of individual,
tangled polymer chains with cross-links between them
so that they do not melt when they are heated
Nanoscience refers to structures that are 1-100nm
in size, in the order of a few hundred atoms
Nanoparticles show different properties
to the same materials in bulk and have a
high surface area to volume ratio
This may lead to the development of new
computers, new catalysts, new coatings,
highly selective sensors, stronger and
lighter construction materials and new
cosmetics such as sun tan creams and
deodorants
Paper chromatography
• Elements and compounds can be
detected and identified using
instrumental methods.
• Instrumental methods are accurate,
sensitive and rapid and are particularly
useful when the amount of a sample is
very small.
• Chemical analysis can be used to identify
additives in foods.
• Artificial colours can be detected and
identified by paper chromatography
Explain: What does the picture show?
Gas chromatography mass
spectroscopy
Gas chromatography linked to mass spectroscopy (GC-MS) is an example of an
instrumental method
•
Different substances, carried by a gas, travel through a column packed with
a solid material at different speeds, so that they become separated
•
The number of peaks on the output of a gas chromatograph shows the
number of compounds present
•
The molecular mass is given by the molecular ion peak
•
The position of the peaks on the output indicates the retention time
•
A mass spectrometer can identify substances very quickly and accurately
and can detect very small quantities
•
Gas chromatography