P1

• Atom


  Positively charged nucleus containing protons and neutrons, surrounded by negatively charged electrons
• How the atomic model has changed over time

  1. 1800 - Dalton said everything was made of tiny spheres called atoms, that could not be divided

  2. 1897 - JJ Thomson discovered the electron and The Plum Pudding Model was hypothesised

  3. 1911 - Rutherford realised most of the atom was empty space and The Gold Foil Experiment was carried out by Geiger and Marsden

  4. 1913 - Rutherford Model

  5. 1913 - Bohr produced the final model of the atom
• Subatomic particles


  • Proton (relative mass 1, relative charge +1)
  • Nucleus (relative mass 1, relative charge 0)
  • Electron (relative mass 0.0005, relative charge -1)
• The typical size of an atom is 1x10^-10 metres with the radius of the nucleus being 10,000 times smaller still
• Nearly all of the mass of the atom is concentrated at the nucleus
• Energy levels


  Electrons lie at different distances from the nucleus
• Density


  Mass per unit volume
• Density depends on the spacing of the atoms in matter (the volume they take up)
• Solids and liquids have similar, higher densities as the space between particles does not change significantly
• Liquids typically have a lower density than solids with one main exception being ice, which is less dense than water
• Gases have much lower densities as the spacing between atoms is much greater
• Gas particles have lots of energy to move, so they occupy a greater volume, decreasing their density compared to solids and liquids
• Mass is conserved during a change in state of a substance
• Physical changes are reversible and are not chemical changes because the material retains its original properties when the change is reversed
• Temperature


  A measure of the average kinetic energy of particles in a system, measured on a relative scale
• Heat


  A form of energy, measured on an absolute scale
• Specific heat capacity (c)

  The energy required to raise the temperature of 1kg of a substance by 1°C (or 1°Kelvin)
• Specific latent heat (l)

  The energy required to change the state of 1kg of a substance without a change in temperature
• Fluid


  A liquid or a gas
• Pressure produces a net force at right angles to any surface
• Temperature and pressure


  Temperature and pressure are proportional when volume is constant
• Volume and pressure


  Volume and pressure are inversely proportional at a constant temperature
• Temperature, volume and work

  Temperature and volume of a fluid are proportional at a constant pressure
• Earth's atmosphere is assumed to be isothermal, meaning it is all the same temperature
• Earth's atmosphere is also assumed to have uniform density for simplification
• Atmospheric pressure


  The total weight of the air above a unit area at a certain altitude, decreasing as height above Earth's surface increases
• As a helium space balloon rises into space, the helium gas exerts a greater force from the inside of the balloon than the thinner air from the outside, causing the balloon to expand
• An object will float if its weight is less than the weight of the fluid it displaces
• An object will sink if its weight is greater than the weight of the fluid it displaces
• Buoyancy force


  The upwards force exerted by a liquid on a partially submerged object, counteracting the weight of the floating object