Igcse chemistry

• States of Matter


  • Solids
  • Liquids
  • Gases
• Solids


  • Have a definite shape
  • Have a fixed volume
  • Particles can vibrate about their fixed positions
  • Particles are arranged regularly in a lattice
• Liquids


  • Take the shape of their container
  • Have a fixed volume
  • Particles can move past one another
  • Particles are randomly arranged
• Gases


  • Take the shape of their container
  • Have no fixed volume
  • Particles are mobile and move randomly
  • Particles are randomly arranged
• States of Matter are the different forms in which matter can exist
• Boiling and Evaporation


  1. Endothermic processes

  2. Involve the conversion of a liquid into a gas

  3. Allow molecules to move further apart from each other
• Boiling


  • Happens at a set temperature called the boiling point
  • Occurs throughout the liquid
• Evaporation


  • Occurs at any temperature below the boiling point and above the freezing point (liquid)
  • Only occurs at the surface
  • A slow process
• Condensation


  1. The process by which a gas converts into a liquid

  2. Happens at the same temperature as the boiling point

  3. As temperature decreases, the energy of particles will decrease, making them move more slowly

  
• Freezing, Melting and Sublimation

  1. Melting: Solid converts to liquid at melting point

  2. Freezing: Liquid converts to solid at freezing point

  3. Sublimation: Solid converts to gas or gas converts to solid
• Condensation and Freezing are both energy-given-out reactions
• Cooling Curve


  1. Particles of gas move slower and slower, gas contracts

  2. Particles get closer, intermolecular bonds form at condensation point

  3. Temperature stops falling as energy released by bond formation cancels out energy lost due to cooling

  4. At freezing point, intermolecular bonds between liquid molecules start to develop to form a solid

  5. Temperature remains constant at freezing point until all liquid has solidified
• Heating Curve


  1. Particles of solid start to vibrate faster, solid begins to expand

  2. At melting point, intermolecular bonds between particles begin to break, temperature remains constant until all solid has turned to liquid

  3. Once all solid has turned to liquid, temperature starts to rise again, liquid begins to expand

  4. At boiling point, intermolecular bonds between liquid molecules start to break down to form a gas, temperature remains constant until all liquid has vaporised

  
• Diffusion


  • The net movement of particles from a region of higher concentration to a region of lower concentration as a result of their random movement until equilibrium is reached
  • Rate of diffusion is most rapid in gases > liquids > solids
• Effect of Relative Molecular Mass in Diffusion

  Molecules with lower mass move faster on average than those with higher mass
• Increase in external pressure


  Contraction (decrease) in gas volume

  
• Fall in external pressure


  Expansion (increase) in gas volume

  
• Increase in gas temperature

  Increased kinetic energy of gas molecules, increased internal pressure and increased volume

  
• Decrease in gas temperature

  Decreased kinetic energy of gas molecules, decreased internal pressure and decreased volume
• Element


  A substance made of atoms that share the same number of protons and cannot be broken down into simpler substances by chemical methods
• Compound


  Two or more elements chemically bonded together (in a fixed proportion)
• Mixture


  Two or more elements not chemically bonded together
• Atom


  • Central nucleus containing neutrons and protons, surrounded by electrons in shells
  • Protons have relative mass 1 and relative charge +1
  • Neutrons have relative mass 1 and relative charge 0
  • Electrons have relative mass 1/1840 and relative charge -1
  • Overall atom charge is neutral
• Proton Number (Atomic Number)


  Number of protons in the nucleus of an atom, unique to each element
• Nucleon Number (Mass Number)


  Total number of protons and neutrons in the nucleus of an atom
• AZX Notation


  Notation showing proton number (Z) and mass number (A) for an element X
• Electronic Configuration


  • Electrons orbit in shells, with first shell max 2 electrons, subsequent shells max 8 electrons
  • General complete configuration is (2.8.8)
  • Group VIII noble gases have entire outer shell filled
  • Number of outer shell electrons equals group number in Groups I-VII
  • Number of occupied electron shells equals period number
• Isotopes


  Different atoms of the same element with same number of protons but different numbers of neutrons
• Relative Atomic Mass


  Mass of an element relative to 1/12 the mass of a carbon-12 atom, calculated from the abundance of naturally occurring isotopes

  
• Metallic Bonding


  • Electrostatic attraction between positive metal ions and a "sea" of delocalised electrons
  • Gives good electrical conductivity, high melting/boiling points, malleability, ductility
• Diamond


  • Each carbon atom joined to 4 others, high melting/boiling points, transparent, cannot conduct electricity, hard, giant lattice structure, used for cutting tools
• Graphite


  • Each carbon atom joined to 3 others, high melting/boiling points, contains delocalised electrons so can conduct electricity, soft, layers held by weak intermolecular forces, used as lubricant and electrode
• Silicon(IV) Oxide


  • Similar tetrahedral structure to diamond, hard, high melting/boiling point, rigid, does not conduct electricity
• Covalent Bond


  Pairs of electrons shared between two atoms, leading to noble gas electronic configuration
• Types of Covalent Bonds

  • Single Bonds
  • Double Bonds
  • Triple Bonds
• Covalent Compounds


  • Have weak intermolecular forces but strong covalent bonds
  • Have low melting and boiling points, require less energy to overcome intermolecular forces
• Silicon Dioxide (SiO2)


  • High melting and boiling point - More energy to overcome
  • Rigid Tetrahedral Structure
  • Does not conduct electricity
• Covalent bonding in Silicon Dioxide

  • Each Silicon atom is covalently bonded with 4 Oxygen Atoms
  • Each Oxygen atom is covalently bonded with 2 Silicon Atoms
• Covalent Bond


  Pairs of electrons shared between two atoms leading to noble gas electronic configuration (2.8.8)
• Different Types of Covalent Bonds

  • Single Bonds - e.g., Chlorine
  • Double Bonds - e.g., Carbon Dioxide
  • Triple Bonds - e.g., Nitrogen