Chapter 2: Atoms

Chapter 2: Atoms

1. Dilution of coloured substances

   • Potassium manganate crystals dissolve in water- purple solution is formed
     • When diluted, colour fades but doesn't dissapear until many dilutions
     • Large number of particles of Potassium Manganate in very small amount of solid. Particles of K Manganate must be very small

2. Diffusion

   • Particles spreading to fill space
     • Example
       • Bromine from one flask to another. After 5 minutes, bromine gas has diffused between both flasks. Air and bromine particles are moving randomly and there are large gaps between particles- they can easily mix together
     • Takes place in liquids also, but slower
       • Because liquids are closely packed together and move more slowly than in a gas.

3. Atoms and molecules

   • Atoms are made up of sub-atomic particles
     • Protons: Charge +1, Mass 1 Electons: -1, Mass 1/1836 Neutron: 0, 1 The only atom with no neutrons is the simplest isotype of H
   • Molecules are made up of 2+ atoms covalently bonded together
     • Noble gas' (He, Neon, Radon etc.) exist as atoms at room temperature and pressure so the atom and molecule are the same. Molecule like noble gas' are called monoatomic molecules. 

4. Elements, compounds and mixtures

   • Elements
     • Elements have different, individual, chemical properties.
     • Iron Filings
       • Element,  Grey Powder Attracted to magnet Reacts with HCl to form H gas
     • Sulphur
       • Element,  Yellow Powder Not magnetic Does not react with HCl
   • Mixture
     • Iron and sulphate
       • Mixture Mix of grey and yellow powder Iron attracts, Sulphur doesn't Grey powder forms H gas with HCl. Yellow powder doesn't react
   • Compounds
     • Iron Sulphide
       • Compound Dark grey solid Not attracted to magnet Reacts with HCl to form Hydrogen Sulfide ( H2S)