Giant Covalent Structure

Giant Covalent Structure

Multiple Choice

Why is diamond strong?

• It's made of carbon

• It doesn't conduct electricity

• It forms 4 strong covalent bonds

• So it can cut glass

Multiple Choice

What structure is shown in the diagram?

• Diamond

• Graphite

• Carbon fiber

• Carbon nanotubes

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​Allotropes - different crystalline or molecular forms of the same element

A - ​buckmisterfullerene (C₆₀)

​B - nanotubes

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Multiple Choice

Define the term allotropes

• Atoms with same proton number but different number of neutrons

• Atoms with same proton number but different mass number

• Atoms in different arrangement in structure

• Atoms in different arrangement and different physical form

Multiple Choice

What element are diamond and graphite made up of?

• Sodium

• Carbon dioxide

• Carbon

• Silicon

Multiple Choice

Why does graphite conduct electricity?

• Ions are free to move to carry the charge

• Atoms can move

• Free electrons that can carry the charge

Multiple Choice

Formulae of these might include H₂O each molecule contains 1 O and 2H atoms

• simple covalent molecules

• metallic

• giant covalent

• ionic

Multiple Choice

Melting points are very high – a large amount of energy is needed to break all the covalent bonds.

• simple covalent molecules

• metallic

• giant covalent

• ionic

Multiple Choice

Low melting and boiling points which increase with increasing molecule size due to increased intermolecular forces.

• simple covalent molecules

• metallic

• giant covalent

• ionic

Multiple Choice

Elements such as Silicon, diamond and graphite. Compounds include SiO₂.

• simple covalent molecules

• metallic

• giant covalent

• ionic

Open Ended

Why graphite can conduct electricity?

Multiple Choice

Which answer shows the correct number of C-C covalent bonds in its allotropes?

• Diamond 3, Graphite 3

• Diamond 4, Graphite 3

• Diamond 3, Graphite 4

• Diamond 4, Graphite 4

Multiple Choice

Silicon (IV) oxide has properties that similar to graphite.

• TRUE

• FALSE

Other Allotropes of Carbon

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What are fullerenes?

• They are allotropes of carbon in the form of hollow spheres or tubes.

• Their structure are similar to graphite’s structure. Each carbon atom is bonded to three other carbon atoms.

What are fullerenes?

• They contain rings of carbon atoms arranged in hexagon and in addition many contain rings of carbon atoms arranged in pentagons.

Buckminsterfullerene

• This is the first fullerene discovered, which is C-60.

• This molecule has the shape of a football.

• The carbon atoms are arranges at the corners of 20 hexagons and 12 pentagons.

Buckminsterfullerene

• The bond where two hexagons join are shorter than the bonds between the hexagons and pentagons.

• Like in graphite, some of the elctrons in this molecule are delocalised, but to lesser extent than in graphite.

Properties of Buckminsterfullerene

• Low sublimation point. This is because there are weak Van der Waals’ forces in between each of this molecule and no continuous layered giant structure as in graphite.

• It’s relatively soft because it doesn’t require much energy to overcome the weak intermolecular force.

• It’s a poor conductor of electricity because the extent of electron decolisation is lower.

Nanotubes

• Fullerene of hexagonally arranged carbon atom like a single layer of of graphite bent into the form of a cylinder

• Nanotubes has been made with thicker wall with several tubes inside one another, although the diameter is small it can be made very long.

Characteristic Properties of Nanotubes

• High electrical conductivity along the long axis of the cylinder. This is because, like graphite, some of the electron are delocalised and are able to move along the cylinder when a voltage is applied.

• Very high tensile strength when a force is applied along the long axis of the cylinder. They can be up to 100 times stronger that steel of the same thickness.

• High melting point about 3500 ^oC, because there is strong covalent bonding throughout the structure

Graphene

• A thin layer of graphite.

• It is a single, tightly packed layer of carbon atoms that are bonded together in a hexagonal honeycomb lattice

• The hexagonally arranged sheet of carbon atoms is not completely rigid and it can be distorted.

  
  

Properties of Graphene are similar to Graphite

• Graphene is the most chemically reactive form of carbon. Single sheets of grapheme burn at very low temperatures and are much more reactive than graphite.

• Graphene is extremely strong for its mass.

• For a given amount of material, graphene conducts electricity and heat much better than graphite.

Graphene

• A one square meter hammock made of graphene could support a 4kg cat, but weigh only as much as the cat’s whisker. Graphene can be used in tiny electrical circuits and for tiny transistors, touchscreens, solar cells and other energy storage devices.