11/10/2015
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C2-B
Explain why although the bonds between atoms in a
simple covalent compounds are strong, simple covalent
compounds are usually found as gases ?
Substances that consist of simple molecules have only
weak forces between the molecules (intermolecular
forces). It is these intermolecular forces that are
overcome, not the covalent bonds, when the substance
melts or boils.
Why do substances that consist of simple molecules eg
CO2 not conduct electricity ?
Substances that consist of simple molecules do not
conduct electricity because the molecules do not have an
overall electric charge.
Explain why ionic compounds have high melting and
boiling points ?
Ionic compounds have regular structures (giant ionic
lattices) in which there are strong electrostatic forces in all
directions between oppositely charged ions. These
compounds have high melting points and high boiling
points because of the large amounts of energy needed to
break the many strong bonds.
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Explain why ionic compounds can conduct electricity when
melted or dissolved ?
When melted or dissolved in water, ionic compounds
conduct electricity because the ions are free to move and
carry the current.
Explain why giant covalent structures or macromolecules
e.g. diamond , graphite, silicon dioxide have high melting
points ?
All the atoms in these structures are linked to other atoms
by strong covalent bonds and so they have very high
melting points.
What is the name of this
covalent macromolecule?
Diamond
What is the name of this
covalent macromolecule?
Silicon dioxide
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What is the name of this
covalent macromolecule?
Graphite
How many bonds does carbon form with other carbon
atoms in diamond ?
4
Explain why graphite is soft and slippers ?
In graphite, each carbon atom bonds to three others,
forming layers. The layers are free to slide over each other
because there are no covalent bonds betweenthe layers
and so graphite is soft and slippery
What type of bonding do you find between the layers in
graphite ?
Weak intermolecular forces
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Fullerenes are based on what shape of
rings of carbon atoms.
Hexagonal
Give 4 uses of fullerenes.
Fullerenes can be used for :
1. drug delivery into the body,
2. in lubricants,
3. as catalysts,
4. in nanotubes for reinforcing
materials, eg in tennis rackets.
Explain how graphite is similar to a metal ?
In graphite, one electron from each carbon
atom is delocalised.
These delocalised electrons allow graphite to conduct heat
and electricity.
Explain why metals are good conductors of heat and
electricity ?
Metals conduct heat and electricity because of the
delocalised electrons in their structures that are free to
move
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Explain why most metals can be bent and shaped ?
The layers of atoms in metals are able to slide over each
other and so metals can be bent and shaped.
Why are alloys stronger than pure metals ?
Alloys are usually made from two or more different
metals. The different sized atoms of the metals distort the
layers in the structure, making it more difficult for them to
slide over each other, and so make alloys harder than
pure metals.
What are shape memory alloys and give an example ?
Shape memory alloys can return to their original shape
after being deformed, e.g. Nitinol used in dental braces.
Explain why low density and high density poly(ethene)
have different properties.
Low density (LD) and highdensity (HD) poly(ethene) are
produced using
different catalysts and reaction conditions.
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Explain the properties of thermosoftening polymers in
terms of intermolecular forces.
Thermosoftening polymers consist of individual, tangled
polymer chains held together by weak intermolecular
forces so are free to slide over each other and have a low
melting point.
Explain why thermosetting polymers do not melt when
heated.
Thermosetting polymers
consist of polymer chains with cross-links between them
so that they do not melt when they are heated.
State the main property of LD polyethene and list 2 of its
uses.
It is flexible
Used to make bottles and bags
State the main property of HD polyethene and list 2 of its
uses.
It is rigid
Used to make water tanks and drainpipes
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Describe the reaction conditions used to make LD
polyethene
High temperature (200 degrees) and high pressure
Describe the reaction conditions used to make HD
polyethene
Lower temperature and lower pressure and catalyst.
Describe what nanoscience structures refer to
Nanoscience refers to structures that are
1–100 nmin size, of the order of a few hundred atoms.
Describe the relationship between surface area and
volume in nanoparticles
Nanoparticles have a high surface area to
volume ratio
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List 6 uses of nanoparticles
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1. new computers,
2. new catalysts,
3. new coatings,
4. highly selective sensors,
5. stronger and lighter construction materials,
6. new cosmetics such as sun tan creams and deodorants.
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