Topic 2 – Bonding, Structure, and The Properties of Matter

• Compounds


  Substances in which 2 or more elements are chemically combined
• Types of strong chemical bonds

  • Ionic
  • Covalent
  • Metallic
• Ionic bonding


  • Particles are oppositely charged ions
  • Occurs in compounds formed from metals combined with non-metals
• Covalent bonding


  • Particles are atoms which share pairs of electrons
  • Occurs in most non-metallic elements and in compounds of non-metals
• Metallic bonding


  • Particles are atoms which share delocalised electrons
  • Occurs in metallic elements and alloys
• Formation of ionic compounds

  1. Metal atoms lose electrons to become positively charged ions

  2. Non-metal atoms gain electrons to become negatively charged ions
• An ion is an atom that has lost or gained electron(s)
• Ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 gain full outer shell of electrons, so they have the same electronic structure as a noble gas (Group 0 element)
• Electron transfer during the formation of an ionic compound

  • Dot and cross diagram (e.g. for NaCl)
• Ionic compounds


  • Giant structure of ions
  • Held together by strong electrostatic forces of attraction between oppositely charged ions
  • Forces act in every direction since the structure is in 3D
• Covalent bonding


  Atoms share one or more pairs of electrons
• Small molecules with covalent bonds

  • HCl
  • H2
  • O2
  • Cl2
  • NH3
  • CH4
• Polymers


  Large covalently bonded molecules
• Giant covalent structures (macromolecules)


  Many atoms covalently bonded in a lattice structure
• Examples of giant covalent structures

  • Diamond
  • Silicon dioxide
• Metallic bonding


  Positive ions (atoms that have lost electron(s)) and delocalised electrons arranged in a regular pattern
• Delocalised electrons in metallic bonding

  • Free to move through the structure
  • Shared through the structure, making metallic bonds strong
• The three states of matter

  Solid, liquid and gas

  
• Melting and freezing


  Take place at the melting point
• Boiling and condensing


  Take place at the boiling point
• Particle theory


  • Can help to explain melting, boiling, freezing and condensing
  • The amount of energy needed to change state depends on the strength of the forces between the particles
  • The nature of the particles involved depends on the type of bonding and the structure of the substance
  • The stronger the forces between the particles the higher the melting point and boiling point of the substance
• Limitations of the simple particle model include that there are no forces, all particles are represented as spheres, and the spheres are solid
• State symbols


  Solid (s), liquid (l), gas (g), aqueous (aq)
• Ionic compounds


  • Have regular structures (giant ionic lattices)
  • Have strong electrostatic forces of attraction in all directions between oppositely charged ions
  • Have high melting and boiling points
  • Conduct electricity when melted or dissolved in water, but not when solid
• Small molecules


  • Usually gases or liquids with low boiling and melting points
  • Have weak intermolecular forces between the molecules
  • Larger molecules have higher melting and boiling points
  • Don't conduct electricity
• Polymers


  • Have very large molecules
  • Atoms in the polymer molecules are linked by strong covalent bonds
  • Intermolecular forces between polymer molecules are relatively strong, so they are solids at room temperature
• Giant covalent structures


  • Are solids with very high melting points
  • All atoms are linked by strong covalent bonds that must be overcome to melt or boil
• Giant covalent structures


  • Diamond, graphite, silicon dioxide
• Metals


  • Have giant structures of atoms with strong metallic bonding
  • Most have high melting and boiling points
  • The layers of atoms can slide over each other, so metals can be bent and shaped
• Alloys


  • Made from 2 or more different types of metals
  • The different sized atoms distort the layers in the structure, making it harder for them to slide over each other, so alloys are harder than pure metals
• Metals as conductors


  • Good conductors of electricity because the delocalised electrons carry electrical charge
  • Good conductors of thermal energy because energy is transferred by the delocalised electrons
• Diamond


  Each carbon is joined to 4 other carbons covalently
• Diamond


  • Very hard
  • Has a very high melting point
  • Does not conduct electricity
• Graphite


  Each carbon is covalently bonded to 3 other carbons, forming layers of hexagonal rings which have no covalent bonds between the layers
• Graphite


  • The layers can slide over each other due to no covalent bonds between the layers, but weak intermolecular forces
  • Soft and slippery
• Graphite


  One electron from each carbon atom is delocalised
• Graphite


  • Similar to metals because of its delocalised electrons
  • Can conduct electricity - unlike Diamond, because the delocalised electrons can move
• Graphene


  Single layer of graphite
• Graphene


  • Has properties that make it useful in electronics and composites
  • Very strong because atoms within its layers are very tightly bonded
  • Elastic because the planes of atoms can flex relatively easily without the atoms breaking apart
• Fullerenes


  • Molecules of carbon atoms with hollow shapes
  • Based on hexagonal rings of carbon atoms, but may also contain rings with five or seven carbon atoms