chemistry

• States of Matter are the different forms in which matter can exist
• The three states of matter


  • Solid
  • Liquid
  • Gas
• 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
• Boiling and Evaporation are both endothermic processes
• Boiling

  • Happens at a set temperature called the boiling point
  • Occurs throughout the liquid
  • A relatively faster process
• Evaporation

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

  • The process by which a gas converts into a liquid
  • Happens at the same temperature as the boiling point
• Melting

  • The process in which a solid converts to a liquid
  • Happens at a set temperature called the melting point
• Freezing

  • The process in which a liquid converts to a solid
  • Happens at the same temperature as the freezing point
• Sublimation

  Occurs when a solid has enough energy to convert into a gas or gas converted into a solid
• Cooling Curve

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

  2. Particles get closer together and intermolecular bonds start to form once condensation point is reached

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

  4. Once all gas turned to liquid, temperature starts falling again and liquid begins to contract until freezing point

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

  6. At freezing point, temperature remains constant until all liquid has solidified
• Heating Curve

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

  2. At melting point, intermolecular bonds between particles begin to break

  3. Temperature remains constant until all solid has turned into liquid

  4. Once all solid has turned to liquid, temperature starts to rise again and liquid begins to expand until boiling point

  5. At boiling point, intermolecular bonds between liquid molecules start to break down to form a gas

  6. At boiling point, 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
  • The rate of diffusion is most rapid in gases > liquids > solids
• Effect of Relative Molecular Mass in Diffusion

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


  Contraction (decrease) in volume
• Fall in external pressure


  Expansion (increase) in volume

  
• Temperature increase

  Increased kinetic energy of gas molecules, more hits on container walls, increase in internal pressure and volume

  
• Temperature decrease

  Decreased kinetic energy of gas molecules, less hits on container walls, decrease in internal pressure and volume
• Elements

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

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

  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)

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

  The total number of protons and neutrons in the nucleus of an atom
• Electronic Configurations

  • Electrons orbit in shells, with the first shell having a max capacity of 2 electrons and subsequent shells up to 8
  • Group VIII noble gases have a full outer shell
  • Number of outer shell electrons equals the group number in Groups I to VII
  • Number of occupied electron shells equals the period number
• Isotopes

  • Different atoms of the same element with the same number of protons but different numbers of neutrons
  • Have the same chemical properties but different physical properties like density, boiling point and melting point
• Relative Atomic Mass

  The mass relative to the mass of a carbon-12 atom, calculated using the abundance of naturally occurring isotopes
• Metallic Bonding

  • Electrostatic attraction between positive ions in a giant metallic lattice and a "sea" of delocalised electrons
  • Good electrical conductivity
  • High melting and boiling point
  • Malleability
  • Ductility
• Diamond

  • Each carbon atom joined with four other carbon atoms
  • High melting and boiling points
  • No delocalised/free moving electrons
  • Cannot be scratched easily
  • Transparent
  • Cannot conduct electricity
  • Hard structure
  • Giant lattice arrangement
  • Used for cutting tools
• Graphite

  • Each carbon atom joined with three other carbon atoms
  • High melting and boiling points
  • Contains delocalised/free moving electrons
  • Can be scratched easily
  • Opaque/black
  • Can conduct electricity
  • Soft, layers can slide easily
  • Used as lubricant and electrode
• Silicon (IV) Oxide

  • Similar structure to diamond
  • Hard structure
  • High melting and boiling point
  • Rigid tetrahedral structure
  • Does not conduct electricity
• 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
  • Double Bonds
  • Triple Bonds
• Properties of Covalent Compounds

  • Intermolecular forces are weak but have strong covalent bonds
  • Have low melting and boiling points, require less energy to overcome
• 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
• Different Types of Covalent Bonds

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

  • The intermolecular forces in covalent compounds are weak but have strong covalent bonds
  • Covalent Compounds have low melting and boiling point. They require less energy to break the weak intermolecular forces (same as attractive forces)
  • Poor Electrical Conductivity - No free electrons or ions present to carry an electrical current