4.2 CHEMISTRY

• Ionic bonding

  • Electrons in the outer shell of the metal atom are transferred
  • Metal atoms lose electrons to become positively charged ions
  • Non-metal atoms gain electrons to become negatively charged ions
  • An ion is an atom that has lost or gained electron(s)
• Ionic compounds


  • Are giant structures of ions
  • Held together by strong electrostatic forces of attraction between oppositely charged ions
  • Forces act in every direction due to the 3D structure
• Metallic bonding

  • Consists of positive ions and delocalised electrons arranged in a regular pattern
  • Delocalised electrons are free to move through the structure
  • Shared delocalised electrons make metallic bonds strong
• Types of strong chemical bonds

  • Ionic
  • Covalent
  • Metallic
• Compounds are substances in which 2 or more elements are chemically combined
• Covalent bonding


  • Atoms share one or more pairs of electrons
  • Small molecules like HCl, H2, O2, Cl2, NH3, CH4 have strong covalent bonds
  • Polymers are large covalently bonded molecules
  • Giant covalent structures consist of many atoms covalently bonded in a lattice structure
• Giant covalent structures

  • diamond
  • silicon dioxide
• Electron transfer during the formation of an ionic compound

  Can be represented by a dot and cross diagram
• Ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 gain a full outer shell of electrons, having the same electronic structure as a noble gas (Group 0 element)
• Properties of ionic compounds


  • Have regular structures (giant ionic lattices) with strong electrostatic forces of attraction in all directions between oppositely charged ions
  • Have high melting and boiling points due to the many strong bonds
  • Conduct electricity when melted or dissolved in water as ions are free to move and carry current, but cannot conduct electricity when solid as ions are fixed in place
• Particle theory

  Can help to explain melting, boiling, freezing, and condensing
• Melting and freezing

  Take place at the melting point
• Limitations of the simple model include no forces, all particles represented as spheres, and the spheres are solid
• Energy needed to change state


  Depends on the strength of the forces between the particles of the substance
• Three states of matter

  • Solid
  • Liquid
  • Gas
• Properties of small molecules

  • Usually gases or liquids with low boiling and melting points
  • Have weak intermolecular forces between molecules which are broken in boiling or melting, not the covalent bonds
  • Intermolecular forces increase with the size of the molecules
• Strong forces between particles

  Result in higher melting and boiling points of the substance
• Boiling and condensing

  Take place at the boiling point
• State symbols in chemical equations

  • Solid (s)
  • Liquid (l)
  • Gas (g)
  • Aqueous solutions (aq)
• Nature of particles involved

  Depends on the type of bonding and the structure of the substance
• Polymers

  Have very large molecules, atoms in the polymer molecules are linked to other atoms by strong covalent bonds, intermolecular forces between polymer molecules are relatively strong making them solids at room temperature
• Metals and Alloys

  Metals have giant structures of atoms with strong metallic bonding, most metals have high melting and boiling points, layers of atoms in metals can slide over each other making them bendable and shapeable, alloys are made from 2 or more different types of metals where different sized atoms distort the layers making alloys harder than pure metals
• Metals are good conductors of thermal energy because energy is transferred by the delocalised electrons
• Substances with low boiling and melting points are usually gases or liquids
• Substances consisting of small molecules do not conduct electricity as they do not have an overall electric charge
• Intermolecular forces between molecules are weak and are broken in boiling or melting, not the covalent bonds
• Giant Covalent Structures

  • diamond, graphite, silicon dioxide (silica)
• Metals are good conductors of electricity because the delocalised electrons in the metal carry electrical charge through the metal
• Intermolecular forces increase with the size of molecules, so larger molecules have higher melting and boiling points
• Giant Covalent Structures

  Substances with giant covalent structures are solids with very high melting points, all atoms in these structures are linked to other atoms by strong covalent bonds which must be overcome to melt or boil these substances
• Graphene

  1. Single layer of graphite

  2. Has properties useful in electronics and composites

  3. Very strong and elastic due to tightly bonded atoms within its layers and flexible planes of atoms
• Diamond structure

  Each carbon is joined to 4 other carbons covalently
• Diamond


  • Very hard
  • Very high melting point
  • Does not conduct electricity
• Graphite

  • Layers can slide over each other due to weak intermolecular forces
  • Soft and slippery
  • One electron from each carbon atom is delocalised
  • Similar to metals due to delocalised electrons
  • Can conduct electricity unlike Diamond due to delocalised electrons
• Graphite structure

  Each carbon is covalently bonded to 3 other carbons, forming layers of hexagonal rings with no covalent bonds between the layers
• Uses of carbon nanotubes

  • Can be used as lubricants
  • Can be used for reinforcing materials, for example tennis rackets
  • Can be used to deliver drugs in the body
  • Can be used as catalysts
• Graphene

  Very strong and elastic because atoms within its layers are very tightly bonded and the planes of atoms can flex relatively easily without the atoms breaking apart
• Carbon nanotubes


  • Can be used as lubricants, to deliver drugs in the body and as catalysts
  • Can be used for reinforcing materials, for example tennis rackets
• Fullerenes


  • Molecules of carbon atoms with hollow shapes
  • Based on hexagonal rings of carbon atoms, but they may also contain rings with five or seven carbon atoms
  • The first fullerene to be discovered was Buckminsterfullerene (C60), which has a spherical shape
• Carbon nanotubes


  Cylindrical fullerenes with very high length to diameter ratios