Giant Structures (Cambridge (CIE) IGCSE Chemistry)
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What are giant covalent structures?
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What are giant covalent structures?
Giant covalent structures are macromolecules or giant lattices that consist of a huge number of non-metal atoms with strong covalent bonds in a fixed ratio.
Define allotropes.
Allotropes are different structural forms of the same element, such as diamond and graphite for carbon.
Why does diamond not conduct electricity?
Diamond does not conduct electricity because all of the outer shell electrons are held in the covalent bonds, and there are no freely moving delocalised electrons to carry the current.
True or False?
Graphite is used in pencils, as an industrial lubricant, in inert electrodes, and in cutting tools.
False.
Graphite is used in pencils, as an industrial lubricant, in inert electrodes, and in locks.
Diamond is used in cutting tools.
Describe the structure of graphite
In graphite:
Each carbon atom is bonded to three others.
There are hexagonal layers.
There is one free / delocalised electron per carbon atom.
True or False?
Graphite is harder than diamond.
False.
Diamond is harder than graphite.
State the properties of diamond.
Diamond does not conduct electricity, has a high melting point, and is extremely hard.
What are the properties of graphite?
Graphite conducts electricity and heat, has a high melting point, and is soft and slippery.
Explain why graphite conducts electricity.
Graphite conducts electricity because it has delocalised electrons that can move / flow (throughout the structure)
Why is diamond hard?
Diamond is hard because its rigid, tetrahedral structure contains a lot of covalent bonds that require a large amount of energy to break.
Why is graphite soft?
Graphite is soft because there are weak intermolecular forces betwen the layers, which allows the layers to slide over each other.
What is silicon(IV) oxide? (Extended Tier Only)
Silicon(IV) oxide is a macromolecular compound that occurs naturally as sand and quartz, with the chemical formula SiO2.
How many oxygen atoms does each silicon atom bond with in silicon(IV) oxide? (Extended Tier Only)
In silicon(IV) oxide, each silicon atom forms covalent bonds with 4 oxygen atoms.
True or False?
Silicon(IV) oxide has a tetrahedral structure similar to diamond. (Extended Tier Only)
True.
Silicon(IV) oxide has a tetrahedral structure similar to diamond.
Define a macromolecular compound. (Extended Tier Only)
A macromolecular compound is a substance composed of very large molecules with a repeating structure.
How does silicon(IV) oxide compare to diamond in terms of properties? (Extended Tier Only)
Silicon(IV) oxide has similar properties to diamond, including being very hard, having a very high boiling point, being insoluble in water, and not conducting electricity.
What are two common uses of silicon(IV) oxide? (Extended Tier Only)
Two common uses of silicon(IV) oxide are making sandpaper and lining the inside of furnaces.
True or False?
Silicon(IV) oxide is an expensive material. (Extended Tier Only)
False.
Silicon(IV) oxide is cheap since it is available naturally.
What type of bonding is present in silicon(IV) oxide? (Extended Tier Only)
Silicon(IV) oxide has covalent bonding.
How many silicon atoms does each oxygen atom bond with in silicon(IV) oxide? (Extended Tier Only)
In silicon(IV) oxide, each oxygen atom forms covalent bonds with 2 silicon atoms.
What is another name for silicon(IV) oxide? (Extended Tier Only)
Another name for silicon(IV) oxide is silicon dioxide or silica.
What is metallic bonding? (Extended Tier Only)
Metallic bonding is the strong electrostatic force of attraction between delocalised electrons and positively charged metal ions.
What are delocalised electrons in metals? (Extended Tier Only)
Delocalised electrons are electrons in metals that do not belong to any particular metal atom and are free to move throughout the metal lattice.
Why can metals conduct electricity? (Extended Tier Only)
Metals can conduct electricity because they have free electrons available to move and carry charge.
What allows metals to be malleable and ductile? (Extended Tier Only)
Metals are malleable and ductile because the layers of positive ions can slide over one another.
True or False?
Alloys are created by mixing a metal with another metal or non-metal. (Extended Tier Only)
True.
Alloys are created by mixing a metal with another metal or non-metal.
Why do metals have high melting and boiling points? (Extended Tier Only)
Metals have high melting and boiling points because they contain many strong metallic bonds, which require a lot of heat energy to overcome.
Describe the structure of a metal. (Extended Tier Only)
Metal structures are positive metal ions arranged in a regular pattern, with a "sea" of delocalised electrons moving freely between them.
True or False?
Metallic bonds are strong due to the attraction between negative metal ions and delocalised electrons. (Extended Tier Only)
False.
Metallic bonds are strong due to the attraction between positive metal ions and delocalised electrons.