6129293
Descripción
Fichas por Mel Hughes, actualizado hace más de 1 año
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Creado por Mel Hughes
hace más de 8 años
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| Pregunta | Respuesta |
| Why do ionic solids have high melting points? | They have giant structures with strong electrostatic forces that hold the ions together and a lot of energy is needed to overcome the forces |
| Why can ionic substances conduct electricity when molten or when dissolved in water? | The ions can move freely and carry the charge |
| Why does petrol not conduct electricity? | The molecules in petrol have no overall charge |
| Why are substances with large molecules more likely to be liquids or solids at room temperatures? | The intermolecular forces are greater for larger molecules |
| Why do substances with giant covalent structures have very high melting points? | Every atom is joined to several other atoms, many strong covalent bonds have to be broken and so it takes a large amount of energy to melt the giant structure |
| Give 2 similarities between diamond and graphite | Forms of carbon; giant covalent structures or covalent bonding |
| Give 2 differences between diamond and graphite | Carbon atoms in diamond are bonded to four other carbon atoms, only to three other atoms in graphite; diamond is three dimensional, graphite is opaque; graphite is a good conductor of electricity, diamond is a poor conductor; graphite has delocalised electrons, diamond does not, graphite has intermolecular forces, diamond does not |
| Give 2 similarities between graphite and fullerenes | Forms of carbon, hexagonal rings of atoms |
| Give 2 differences between graphite and fullerenes | Graphite is a giant structure, fullerenes are molecules; graphite is two dimensional, fullerenes are three-dimensional/cage like; graphite forms large particles, many fullerenes are nano -sized |
| Why can metals be made into wires? | When stretched, the atoms slide into new positions without breaking apart |
| Give two reasons why alloys can be more useful than pure metals | When stretched, the atoms slide into new positions without breaking apart |
| Why are metals good conductors of electricity? | Delocalised electrons move rapidly through the metal structure |
| Why do LD and HD poly(ethene) have different properties? | They are made using different reaction conditions; they have different structures or differently shaped molecules |
| What is the main difference in the structures of thermosoftening and thermosetting polymers? | Thermosoftening polymers have no cross-links or no covalent bonds between the polymer chains, thermosetting polymers have cross-links |
| What allows thermosetting polymers to be remoulded? | The weak intermolecular forces between the chains (are overcome by heating) |
| What is a nanoparticle? | A very small particle that is a few nanometers in size, or made of a few hundreds of atoms |
| Scientists have developed a new deodorant containing nanoparticles. What should be done before it is sold for people to use? | Its effects on people and the environment should be researched/tested (to ensure it is safe to use) |
| Why does it take a lot of energy to melt sodium chloride? | It has a giant ionic structure with strong electrostatic forces/bonds that hold the ions firmly in position and that need a lot of energy to overcome/break them |
| Why are compounds like methane, CH4 and ammonia, NH3, gases at room temperature? | They are made of small molecules or covalent bonds act only between the atoms within a molecule |
| Polymers made from different monomers have different properties. Explain why | Different monomers change the structure of the polymer chains or the polymer chains have different shapes or structures |
| Some dental braces are made from shape-memory alloys. What is meant by a 'shape-memory alloy'? | An alloy (mixture of metals) that can be bent/deformed and changes back to its original shape when heated |
| Explain why diamonds are very hard | Every carbon atom is covalently/strongly bonded to four other carbon atoms in a giant (3-D) covalent structure |
| Why do ionic compounds need to be molten or in solution to conduct electricity? | The ions cannot move in the solid, but become free to move in the molten liquid or in solution |
| Explain why a block of copper can be hammered into a sheet | The atoms are in layers. The layers slide over each other, into the new shape, without breaking apart |
| Silver nanoparticles are used in some socks to help prevent bad smells How are silver nanoparticles different from ordinary silver particles? | They are very much smaller, have a much greater surface area |
| Suggest why a sock manufacturer would use nanoparticles instead of ordinary silver particles | They are more effective (because of their greater surface area), needs to use much less silver (so it is cheaper), easier to attach to sock fibres |
| Explain why thermosetting polymers are often used to make handles for cooking pans | They do not soften/melt when they get hot, they are good insulators (of heat), they can be moulded into shape but then are rigid/hard |
| Explain how the atoms in a metal are bonded to each other | The outer electrons delocalise, leaving a lattice of positive ions; the delocalised electrons strongly attract the positive ions and hold them in position |
| Why can graphite conduct electricity? | There are delocalised electrons in graphite or one electron from each carbon atom is delocalised; the delocalised electrons carry the electrical charge |
| Explain what is meant by 'intermolecular forces' | Forces between molecules (that are much weaker than covalent bonds within the molecules) |
| C60 is a fullerene. What are fullerenes? | Forms of carbon, with large molecules, based on hexagonal rings of carbon atoms, often cage-like structures, can be nano-sized, have many useful applications |
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