Flashcards
C2-B
Cards in this deck (28)
- 1Explain 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.
- 2Why 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.
- 3Explain 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.
- 4Explain 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.
- 5Explain 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.
- 6What is the name of this covalent macromolecule?Diamond
- 7What is the name of this covalent macromolecule?Silicon dioxide
- 8What is the name of this covalent macromolecule?Graphite
- 9How many bonds does carbon form with other carbon atoms in diamond ?4
- 10Explain 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
- 11What type of bonding do you find between the layers in graphite ?Weak intermolecular forces
- 12Fullerenes are based on what shape of rings of carbon atoms.Hexagonal
- 13Give 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. - 14Explain 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. - 15Explain 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
- 16Explain 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.
- 17Why 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.
- 18What 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.
- 19Explain 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. - 20Explain 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.
- 21Explain 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. - 22State the main property of LD polyethene and list 2 of its uses.It is flexible
Used to make bottles and bags - 23State the main property of HD polyethene and list 2 of its uses.It is rigid
Used to make water tanks and drainpipes - 24Describe the reaction conditions used to make LD polyetheneHigh temperature (200 degrees) and high pressure
- 25Describe the reaction conditions used to make HD polyetheneLower temperature and lower pressure and catalyst.
- 26Describe what nanoscience structures refer toNanoscience refers to structures that are
1–100 nmin size, of the order of a few hundred atoms. - 27Describe the relationship between surface area and volume in nanoparticlesNanoparticles have a high surface area to
volume ratio - 28List 6 uses of nanoparticles1. 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.