Chemistry #2

Revision..... (Got information from AQA Science Additional science book)

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  • Created by: Emma
  • Created on: 16-05-11 17:51

Ionic Compounds

Ionic compoundsconsists a giant structure of ions arranged in a lattice. The attractive electrostatic forces between the oppositely charged ions act in all directions and they are also very strong. This holds the ions in the lattice together very tightly.

The attractive forces between the oppositely charged ions in the lattice are very strong, it does take a lot of energy to take the lattice apart. This shows that ionic compounds have a HIGH melting points and boiling points.

When there is enough energy to take the lattice apart the ions are then able to move freely and then the ionic solid will turn into a liquid they have to do this so they can carry the electrical charge through the molten liquid. A solid ionic cannot conduct electricity like this because each ion is held in a fixed position and can't move around.Many ionic compounds will dissolve in water, when this happens the lattice will split up by the water molecules and the ions are free to move.

  • · Ionic compounds will conduct electricity when we melt them or dissolve them in water because their ions can move freely.




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Simple Molecules

  • Substances made up of simple molecules have low melting points and boiling points
  • The forces between simple molecules are weak. These weak intermolecular forces explain thier LOW melting points and boiling points
  • Simple molecules have no overall charge, so they cannot carry electrical charge. Therefore substances containing simple molecules do not conduct electricity.
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Giant covalent structures

Some covalently bonded substances contain GIANT STRUCTURES

Substances such as diamond, graphite and silicon dioxide have giant covalent structures,

These atoms all in these giant lattices are held together by strong covalent bonds in both diamond and silicon dioxide. These 2 structures are very hard, they have HIGH melting points and boiling points and finally they chemically UNREACTIVE.

The Diamond has FOUR bonds and Silicon has THREE

In graphite the bonds are very weak and slippery this is because then they will be able to slide over each other easily. Graphite has TWO bonds.

Graphite can conduct electricity because of the delocalised electrons along its layers.

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Nanoscience and nanotechnology

Nanoscience- This is a new area of science. 'Nano' is a prefix like 'milli' or 'mega'. While 'milli' means 'one-thousandth', 'nano' means one thousand-millionth'- So nanoscience is the sceicne of really tiny things.

Nanoscience at work:

  • Socks that are made from a fabric which contains silver nanoparticles NEVER smell
  • Glass can be coated wiht titanium oxide nanoparticles. Sunshine triggers a chemical reaction that breaks down dirt which then lands on the window.
  • Nanoscience is pure science fiction
  • A type lizard called a gecko can hand upside down from a sheet of glass, that's because the hairs on his feet are so tiny they can use the forces that hold molecules together. Scientists can make sticky tape lined with tiny nano-hairs that work in the same way.
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Questions - In Book

Questions (2.1-2.3)

  • What type of force holds the ions together in an ionic compound?
  • Why do ionic compounds have high melting points and boiling points?
  • How are covalent bonds formed?
  • Why dont molecular substances conduct electricity?
  • Why is Graphite slippery?
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Answers to questions on following page

  • The force attraction
  • Because of how strong the bonds are
  • When they react and share electrons on the outer shell
  • Because there is no overall charge on the molecules
  • So the graphite can slide over one another.
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Nearly Einstein

This is actually quite good! Well done Emma

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