UNIT 1 CHEMISTRY

• Freezing


  Matter changing from a liquid to a solid when energy is removed
• Boiling


  Matter changing from liquid to gas when energy is added

  
• Melting


  Matter changing from solid to liquid when energy is added

  
• Condensing


  Matter changing from gas to liquid when energy is removed
• Evaporating


  Particles at the surface of a liquid becoming free and turning into gas
• Subliming


  Matter changing from solid to gas when energy is added
• Gas pressure

  Total force exerted on the unit area of the wall of a container by gas particles
• Specific heat capacity

  The amount of energy required to raise the temperature of one kilogram of the substance by one degree Celsius
• Specific latent heat of fusion


  Energy needed for a substance to change state from solid to liquid

  
• Specific latent heat of vaporisation

  Energy needed for a substance to change state from liquid to vapour

  
• Pure substance


  Single element or compound not mixed with any other substance
• Isotope


  Atoms of the same element with different numbers of neutrons
• Mass number


  Number of protons + neutrons in the nucleus of an atom

  
• Atomic number


  Number of protons in an atom (equals the number of electrons)
• When a substance changes states, there is no change in mass. This is called the conservation of mass.
• HIGHER ONLY: limitations of the particle model are that it shows no forces between particles, particles are not really solid spheres.
• Gas pressure increases


  When temperature increases because the particles have greater kinetic energy and move faster
• Pure substances melt and boil at specific temperatures – so we can use melting and boiling points to determine if a substance is pure.
• Atoms have a radius of about 1x10-10m
• Small molecules have radii of about 5x10-10m (0.5nm)
• Protons have a relative mass of 1 and a charge of +1.
• Neutrons have a relative mass of 1 and a charge of 0 (they are neutral).
• Electrons have a very small relative mass and a charge of -1.
• The number of protons in an atom is equal to the number of electrons, so the overall charge of the atom is 0 (neutral).
• Electron shell capacity


  • First shell can hold 2 electrons
  • Second shell can hold 8 electrons
  • Third shell can hold 8 electrons
  • Fourth shell can hold 18 electrons
• To work out the number of neutrons in an atom


  Take the atomic number away from the mass number
• Solids are more dense than liquids and gases because they have more particles in the same volume
• Dalton atoms (1804)


  • Spherical atoms that cannot be split up
• Thomson - Plum pudding model (1897)


  • Negatively charged electrons embedded in a ball of positive charge
• Rutherford – nuclear atom (1911)


  • Positive charge found at the centre of the atom, electrons around the outside of the atom, most of the atom is empty space (evidence = firing alpha particles at gold foil)
• Chadwick - Neutrons in the nucleus (1932)


  • Explained why the mass of atoms was greater than could be accounted for by the mass of the protons