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C2 Structure and Properties

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Strucure and Bonding
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Intermolecular force

The forces of attraction between molecules.


Delocalised electrons

Electrons which are free to move, donated by the outershells of the atoms involved.

Bond

An interaction between two atoms either due to an electrostatic force, or the sharing of electrons.


Ion

An atom that has either lost or gained electrons forming a positively charged substance or negatively charged, respectively.


Alloy

Mixture of at least one metal and other elements.

Giant Ionic

Ionic compounds have regular structures. They make giant ionic lattices of oppositely charged ions. These ions experience strong, electrostatic forces of attraction in all directions. This means they have high melting points, as large amounts of energy is needed to break the bonds.


Ionic compounds can conduct electricity only when molten or dissolved in water, as the ions are free to move = charge can flow.

3D Giant Ionic Lattice

Simple Molecules

These have strong covalent bonds within the molecule, but weak intermolecular forces of attraction. This means they are either gas or liquid at room temperature.


They do not conduct electricity as there are no free moving electrons, or ions.

Higher

Diagram showing the intermolecular forces holding simple covalent molecules together

Shape Memory Alloys

All metals can be bent, or shaped, and we call this property: malleable. When we create an alloy, this property usually disappears due to irregularities introduced to the structure. Some alloys, however, retain this property.


Shape-memory alloys can be bent into any shape (like pure metals), but when they are heated - the alloys return to their 'original' shape.


Giant Covalent

These compounds are solid at room temperature. All of the atoms in a giant covalent structure are held together by strong covalent bonds. These bonds have to be broken, by large amounts of energy, to melt or boil these substances.


Diamond is made up of carbon forming four covalent bonds. Graphite is made of hexagonal rings of carbon, each atom forming three bonds. Each atom contributes an electron to the “sea of delocalised electrons”.


Graphite

Higher

Weak forces hold the layers together, so they can slide over each other, thus making graphite a great lubricant.


Only 3 electrons from each carbon atom form strong covalent bonds, leaving one delocalised electron. Graphite has a high melting point, and is a good thermal/electrical conductor.


Fullerenes/Nanotubes

Higher

Graphene is just a single layer of graphite, and is one atom thick.

Fullerenes can be thought of as graphene sheets rolled into a ball, however graphene is made of 6 sided rings, and fullerenes are made of 5 and 6 sided rings. Fullerenes can take the shapes of balls, or other shapes like tubes (nanotubes).


Nanotubes are excellent conductors of heat/electricity and have high tensile strength. They can be used to reinforce materials, as conductors or as catalysts. Fullerenes and nanotubes can be used for medical uses, and other potential uses are being explored. They both have hollow insides, and can be thought of as tiny 'cages'.


Polymers

Low Density Poly(Ethene) [LDPE]

  • made using high pressure and temperature
  • branched polymer chains, can't pack closely

High Density Poly(Ethene) HDPE]

  • made using low pressure and temperature, with a catalyst
  • less branches so can pack closely together
  • higher softening temperature, stronger than LDPE

Thermosoftening Polymers

  • soften quite easily with heating
  • individual polymer chains tangled together

Thermosetting Polymers

  • do not melt well when heated, may burn
  • strong covalent crosslinking bonds between chains

Polymer Bonding

Higher

Atoms in a polymer chain are held together by strong covalent bonds. But the sizes of forces between the individual polymer chains can be quite different.


Thermosoftening plastics have very weak intermolecular forces, and slight heating can break these forces allowing it to become soft. When the polymer cools back down the intermolecular forces cause the chains to move back together and the polymer hardens into its new shape.


Nanoscience

1 nanometre (1 nm) is the same as 0.000000001 m (a billionth of a metre).

A nanoparticle can be anything that is between the sizes of 1 nm to 100 nm. Things this size cannot be seen with a traditional light microscope, and are the size of small molecules.

Nanoparticles have a large surface area to volume ratio, so they:

  • react quickly
  • are useful catalysts

Nanoparticles behave differently from the materials they are made would behave at much larger scales. Titanium dioxide is used in white paint, but titanium dioxide nanoparticles are smaller than light waves, so do not reflect them and therefore cannot be seen. They're used in suncreams to block UV light, and don't make your arms look all white!


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Page last updated: 16/04/2017