Bonding and structure

• 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
• Ionic bonding formation

  1. Metal atoms lose electrons to become positively charged ions

  2. Non-metal atoms gain electrons to become negatively charged ions

  3. 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 can be represented by a dot and cross diagram
• Ionic compounds

  • Giant structure of ions
  • Held together by strong electrostatic forces of attraction
  • Since the structure is 3D, the forces act in every direction
• Covalent bonding

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

  • HCI, H2, O2, CI2, NH3, CH4
• Polymers

  Large covalently bonded molecules
• Giant covalent structures (macromolecules)

  • Consist of many atoms covalently bonded in a lattice structure
  • Examples: diamond, silicon dioxide
• Diagrams to show covalent substances could be dot and cross, shown as repeat units for polymers using a single line to represent a single bond, ball and stick and two-and three-dimensional diagrams
• Metallic bonding

  • Positive ions (atoms that have lost electron(s)) and delocalised electrons arranged in a regular pattern
  • Delocalised electrons are free to move through the structure
  • Delocalised electrons are shared through the structure so metallic bonds are strong
• Three states of matter

  • Solid
  • Liquid
  • 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 from solid to liquid and from liquid to gas depends on the strength of the forces between the particles of the substance
  • 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 theory model include that in the model there are no forces, that all particles are represented as spheres and that the spheres are solid
• State symbols

  In chemical equations, the three states of matter are shown as: solid (s), liquid (l), gas (g) and aqueous (aq)
• Properties of small molecules

  • Substances that consist of small molecules are usually gases or liquids that have low boiling and melting points
  • They have weak intermolecular forces between the molecules. These are broken in boiling or melting, not the covalent bonds
  • The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points
  • Substances that consist of small molecules don't conduct electricity, because small molecules do not have an overall electric charge
• 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 and so these substances are solids at room temperature
• Giant Covalent Structures

  • Substances that consist of giant covalent structures are solids with very high melting points
  • All of the atoms in these structures are linked to other atoms by strong covalent bonds
  • These bonds must be overcome to melt or boil these substances
  • Examples include: diamond and graphite (forms of carbon) and silicon dioxide (silica)
• Properties of metals and alloys

  • Metals have giant structures of atoms with strong metallic bonding
  • Most metals have high melting and boiling points
  • The layers of atoms in metals are able to slide over each other, so metals can be bent and shaped, which can make them less useful for certain things
  • Alloys are 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 in the metal carry electrical charge through the metal
  • 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
• Buckminsterfullerene (C60)


  The first fullerene to be discovered, has a spherical shape
• Carbon nanotubes

  Cylindrical fullerenes with very high length to diameter ratios
• Carbon nanotubes

  • Their properties make them useful for nanotechnology, electronics and materials
• Uses of carbon nanotubes and fullerenes

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

  Particles 1-100 nanometers across, containing a few hundred atoms