C1

• States of matter


  • Depend on the forces between particles
• Solids


  1. Strong form of attraction between particles

  2. Particles held in fixed positions in a regular lattice arrangement

  3. Particles don't move from their positions

  4. Solids keep a definite shape and volume, don't flow like liquids

  5. Particles vibrate more as solid is heated
• Liquids


  1. Some force of attraction between particles

  2. Particles free to move past each other but tend to stick together

  3. Liquids don't keep a definite shape, flow to fill container

  4. Particles in constant random motion, move faster as liquid is heated
• Gases


  1. Next to no force of attraction between particles

  2. Particles travel in straight lines, only interact when colliding

  3. Gases don't keep a definite shape or volume, fill any container

  4. Particles move constantly with random motion, move faster as gas is heated
• Particle theory is a great model for explaining the three states of matter, but it isn't perfect
• In reality, the particles aren't solid and they aren't spheres - they're atoms, ions or molecules
• The model doesn't give any idea of the size of the particles, or the space between them
• The model doesn't show any of the forces between the particles, so there's no way of knowing just how strong they are
• Physical changes


  1. Substance changes from one state of matter to another

  2. No new substances are made, the original chemicals just change
• Chemical reactions


  1. Bonds between atoms break

  2. Atoms rearrange to form different chemicals (products)

  3. Compared to physical changes, chemical changes are often hard to reverse
• John Dalton described atoms as solid spheres


  Start of the 19th century
• Thomson concluded atoms contain smaller, negatively charged particles (electrons)


  1897
• Rutherford gold foil experiment

  1. Fired positively charged alpha particles at thin gold foil

  2. Most particles went straight through or were slightly deflected, but some were deflected backwards

  3. Showed the 'plum pudding' model of the atom was wrong
• Rutherford's nuclear atom model

  Tiny, positively charged nucleus at the centre, surrounded by a 'cloud' of negative electrons
• Bohr's model of the atom

  1. Electrons contained in fixed shells/orbits around the nucleus

  2. Each shell has a fixed energy level
• Bohr's model was supported by experiments and helped explain many observations
• Scientific theories have to be backed up by evidence
• As new evidence is found, scientific theories are modified to fit the evidence
• Scientists put their ideas and research up for peer-review
• Subatomic particles


  Protons, neutrons, electrons
• Protons


  • Heavy, positively charged
• Neutrons


  • Heavy, neutral
• Electrons


  • Hardly any mass, negatively charged
• Nucleus


  • Contains protons and neutrons, has positive charge, contains almost all the atom's mass
• Electrons


  • Move in shells/orbitals around the nucleus, determine the size of the atom
• Molecules


  Made up of two or more atoms, can be of the same or different elements
• Simple molecules are tiny, similar in size to atoms
• Atomic number


  Number of protons in an atom
• Mass number


  Total number of protons and neutrons in an atom
• Neutral atoms


  Have equal numbers of protons and electrons, so no overall charge
• Ions


  Atoms that have gained or lost electrons, so have a charge
• Isotopes


  Atoms of the same element with different numbers of neutrons