Structure and Properties

C2 2

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  • Created by: Moodymoo
  • Created on: 17-02-14 16:32

Giant Ionic Structures

  • Electrostatic forces hold the ions together in an ionic compound
  • It takes a lot of energy to break up a giant ionic lattice, there are lots of strong ionic bonds to break
  • Have to overcome electrostatic forces of attraction
  • Means ionic compounds have high melting and boiling points
  • Once enough energy has been supplied to seperate ions from the lattice they are free to move around
  • This is when an ionic solid melts and becomes a liquid, ions are free to move anywhere
  • Can carry an electrical charge (carry it because can move freely)
  • A solid ionic compound cannot carry electricity because they cannot move around
  • Many ionic compounds dissolve in water, the water splits up the lattice, ions can move freely, will conduct electricity
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Simple Molecules

Covalently bonded subsatnces usually have a low boiling and melting points

  • Means many of the substances are liquids or gases at room temperature


  •  Covalent bonds are very strong, atoms within each molecule are held tightly together
  • HOWEVER, each molecule is quite seperate from its neighbouring molecule
  • Attraction between individual molecules in a covalent substance is relatively small
  • Weak intermolecular forces between molecules, overcoming these forces does not require much energy
  • Simple molecules have no overall charge so they cannot conduct electricity
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Giant Covalent Structures

  • Giant covalent structure: form huge networks of atoms held together by covalent bonds
  •  They are very hard, high melting and boiling points, and insoluble in water


  • Graphite carbon atoms are only bonded to three other carbon atoms so they form hexagons which are arranged in giant layers
  • NO COVALENT BONDS BETWEEN THE LAYERS, so the layers slide over eachother easily
  • e.g. like sliding a deck of cards
  • weak intermolecular forces between layers in graphite, so slide over easily
  • Carbon has four electrons in its outer shell, three are joined up so it leaves one spare
  • This electron is free to move along the layers of carbon atoms (delocalised electron) so can conduct electricity
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  • Carbon atoms join together to make large cages which have all sorts of shapes
  • Built up of hexagonal rings of carbon atoms
  • Can place other molecules in carbon atoms, so could deliver drugs to certain parts of the body
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Giant Metallic Structures

  • Can hammer and bend metals into different shapes because atoms in pure metals can slide over eachother easliy
  • Alloys are mixtures of metals, so different size atoms in an alloy
  • Makes it more difficult for layers to slide over eachother
  • Alloys are harder

Properties of metals

  • Positive ions in a metal's giant structure are held together by a sea of delocalised electrons
  • Electrons are a bit like glue; their negative charge between the positively charged ions holds the ions in position
  • Electrons can move around the whole lattice though, because they move and hold metal ions together, the lattice will distort
  • Delocalised electrons means they are good conductors of heat and electricity
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Shape Memory Alloys

  • When you heat these alloys up, they return to their original shape
  • They 'remember' their old shape
  • e.g. dentists make braces to move teeth back
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Properties of Polymers

Properties depend on:

  • monomers used to make it
  • conditions reaction is carried out

Different reaction conditions:

  • Two types of poly(ethene); high density and low density
  • High pressure and a trace of oxygen forms LD ethene, polymer chains are branched and they cant pack closely together
  • A catalyst at 50'C and a slightly raised pressure makes HD ethene. They make straighter poly(ethene) molecules and can pack more closely together (stronger than LD)


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Thermosoftening and Thermosetting Polymers

Thermosoftening polymers

  • Soften or melt easily when heated
  • Cool back to original shape
  • Made up of individual polymer chains tangled together

Thermosetting polymers

  • Not soften when heated but will char eventually
  • They have strong covalent bonds forming 'cross links' between polymer chains
  • Monomers make covalent bonds between polymer chains
  • The bonds stops the polymer from softening
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Bonding in Polymers

  • Atoms in polymer chains are held together by strong covalent bonds
  • The size of the forces between polymer molecules can be different
  • In thermosoftening, the forces between the polymer chains are weak, when we heat the polymer the weak intermolecular forces break
  • When it cools, the intermolecular forces bring the polymer molecules back together
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  • The study of small particles that are between 1 and 100 nanometres in size
  • 1 nanometre = 10-9 metres
  • Nanoparticles behave differently to the materials they are made from on a larger scale


  • Cosmetics, the nanoparticles go deeper into the skin so uses include creams, sun tan creams and deodrants
  • Delivery of drugs in a nanoparticle cage, so the drug goes to where it needs to

Possible risks:

  • Large surface area could make them dangerous, a spark could cause an explosion
  • If they are used more and more they may go into the air around us and breathing them in would damage the lungs
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