P1: Matter

P1: Matter

1. History of the Atom

   • Atoms are the tiny particles of matter which make up everything
     • Matter- anything that has a mass
   • JJ Thomson
     • Found out atoms weren't solid spheres
     • Plum pudding model
       • Fruit- negative electrons
       • 'Pudding'- positive part of atom
   • Ernest Rutherford
     • Worked with Geiger and Marsden
       • Fired postively charged alpha particles at an extremely thin sheet of gold foil
         • Most of the particles went straight through the foil
           • Some deflected more than expected
             • Few deflected back the way they had come
               • Rutherford came up with the theory of the NUCLEAR ATOM
                 • Most of the mass of an atom is concentrated in a tiny, positively charged nucleus at the centre
                   • Surrounded by a 'cloud' of negative electrons
                     • Doesn't this mean that the electrons (negative charge) would be attracted to the nucleus (positive charge)?
                       • This would cause the atom to collapse
                       • Niels Bohr
                         • Proposed a new model where the electrons are in shells
                           • Suggested that electrons can only exist in these shells (fixed orbits)
           • They passed through the empty space
             • Most of the atom is empty space

2. Modern Model of the Atom

   • The nucleus contains protons (positive) and neutrons (neutral) - gives it an overall positive charge
   • Most of the mass is in the nucleus
     • Nuclear radius of the nucleus = 1x10-15
     • Mass of the atom = 1x10-23
       • Depends on the element
     • The negative electrons give the atom its overall size
       • The electrons whizz around outside the nucleus really quickly
     • Diameter of the atom = 1x10-10
       • The nuclear radius is around 10,000 times smaller than the atomic radius

3. Density

   • Density relates the mass of a substance/object to how much space it takes
   • Doesn't vary with shape or size
   • Practical
     • !. Measure the mass of the solid using a mass balance./ mass of liquid using a measuring cylinder
       • 2. To measure the volume of a solid cuboid measure the length, width and height and multiply them together
         • 3. Apply the formula to find the density
       • Regular object
     • Irregular object:
       • !. Use eureka (Archimedes) can to measure volume
         • 2, Measure mass on balance
           • 3. Apply formula
   • To measure the density of a substance, measure the mass and volume of a sample of the substance and use the formula
     • Density = Mass/Volume

4. Particle Theory and States of Matter

   • Three states of matter
     • Solid
       • Strong forces of attraction between particles
       • Fixed, regular arrangement
         • Close together
       • Particles don't have much energy in their kinetic energy stores
       • Can only vibrate about their fixed positions
     • Liquid
       • Weaker forces of attraction
       • Particles are close together, but they move past each other
       • Irregular arrangement
       • More kinetic energy in their energy stores than SOLIDS
       • Move in random directions at low speeds
     • Gas
       • Almost no forces of attraction between particles
       • Particles have more kinetic energy in their energy store than LIQUIDS
       • Free to move
       • Travel in random directions at high speeds
   • Conservation of Mass
     • When a substance changes state, its mass doesn't change but its volume does
       • This means that its density changes also
         • Solids are the most dense
         • Gases are the least dense