C2-B

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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.
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
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
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
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.
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
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
List 6 uses of nanoparticles 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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