Atoms

Created by: Brooke
Created on: 15-07-13 10:51

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Atoms
- Dilution of coloured solutions
  - When potassium manganate(VII) crystals are disolved in water, a purple solution is formed. A very few tiny crystals can produce a highly intense colour
    - When this solution is diluted several times, the colour fades, but does not disappear until a lot of dilutions are made
      - this indicates that there are a large number of particles of potassium manganate(VII) in a very small amount of solid
        if this is true, then the particles of potassium manganate(VII) must be very tiny
- Diffusion
  - Particles will move to fill the space available to them. They can do this in both liquids and gases.
  - An example is the diffusion of bromine from one flask to another.
    - After 5 minutes the bromine gas has diffused into the left-hand flask
      - This happens because both air and bromine particles are moving randomly and there are large gaps between the particles
        the particles can therefore easily mix together
  - Diffusion also takes place in liquids, only more slowly since the particles in a liquid are closely packed together and they move more slowly than in a gas
- Atoms and molecules
  - ATOMS are made up of smaller, sub-atomic particles called protons, neutrons and electrons
  - Most molecules are made up of two or more atoms covalently bonded together
    - However, the noble gases (helium, neon, argon, krypton, xenon and radon) exist at room temperature and pressure, so for them the atom and the molecule are the same
  - Molecules that contain only one atom are called MONATOMIC MOLECULES
- Elements, Compouds and Mixtures
  - Compounds are chemicals made from atoms of different elements joined by chemical bonds. They can only be separated by a chemical reaction.
    - Elements, and compounds have their own chemical proprties. The properties of a compound are likely to be different from the elements that have been used to make it
    - Since the elements in a compound are chemically joined together, they can only be sparated from one another by carrying out a chemical reaction
      - Sometimes heating the compound will be sufficient to make the reaction happen. For example, mercury oxide decomposes into mercury and oxygen on heating
        This is known as THERMAL DECOMPOSITION
      - On another occasion, electricity will decompose the compound the compound. For example, if an electric current is passed through molten lead(II) bromide, it breaks down into lead and bromine
        This is known as ELECTROLYSIS
  - A mixture is made from different substances that are not chemically joined.
    - a mixture will have the properties of each substance that has been used to make it
    - Separation of mixtures
      - Filtration
        To separate an undisolved solid from a mixture of the solid and a liquid/solution (e.g sand from a mixture of sand and water
      - Evaporation
        To separate a dissolved solid from a solution, when the solid has similar solubility in both cold and hot solvent (e.g sodium chloride from a solution of sodium chloride in water)
      - Crystalisation
        To separate a dissolved solid from a solution, when the solid is much more soluble in hot solvent than in cold (e.g copper(II) sulfate from a solution of copper(II) in water)
      - Simple Distillation
        To separate a liquid from a solution (e.g water from a solution of sodium chloride in water)
      - Fractional Distillation
        To separate two or more liquids that are miscible with one another (e.g ethanol and water from a mixture of the two)
      - Paper Chromatography
        To separate substances that have different solubilities in a given solvent (e.g different coloured inks that have been mixed to make black ink)

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Atoms

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