bonding and properties 2

• 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 bond

  1. Metal atoms lose electrons to become positively charged ions

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


  An atom that has lost or gained electron(s)
• Ions produced by


  • Metals in Groups 1 and 2
  • Non-metals in Groups 6 and 7
• Ions produced gain full outer shell of electrons, so they have the same electronic structure as a noble gas (Group 0 element)
• Representation of ionic bond formation


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

  A giant structure of ions held together by strong electrostatic forces of attraction between oppositely charged ions
• Ionic compounds

  • Since the structure is in 3D, the forces act in every direction
  • An example is sodium chloride (NaCl) with Na+ (small blue particles) and Cl- (larger green ones)
• Covalent bonding

  When atoms share one or more pairs of electrons
• Polymers


  Large covalently bonded molecules
• Giant covalent structures (macromolecules)

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


  • Diamond
  • Silicon dioxide
• Melting and freezing


  Take place at the melting point
• Diagrams to show these 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
• Boiling and condensing


  Take place at the boiling point
• Metallic bonding

  The bonding in a metal consists of positive ions (atoms that have lost electron(s)) and delocalised electrons arranged in a regular pattern
• States of matter


  • Solid
  • Liquid
  • Gas
• Metallic bonding


  • The delocalised electron system consists of the electrons 'lost from the atoms to form positive ions
  • Delocalised electrons are free to move through the structure
  • The delocalised electrons are shared through the structure so metallic bonds are strong
• 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
• Limitations of the simple particle model include that there are no forces, all particles are represented as spheres, and the spheres are solid
• Aqueous (aq)

  State of matter shown in chemical equations for aqueous solutions
• PMT


  They have weak intermolecular forces between the molecules
• Ionic compounds


  • Have regular structures (giant ionic lattices)
  • Have strong electrostatic forces of attraction in all directions between oppositely charged ions
• Boiling or melting point 


  Breaks the intermolecular forces, not the covalent bonds
• Ionic compounds


  • Have high melting and boiling points
  • Require a lot of energy to break the many strong bonds
• The size of the molecules increases

  The intermolecular forces increase
• The size of the molecules increases

  The melting and boiling points increase
• Ionic compounds


  • Conduct electricity when melted or dissolved in water because the ions are free to move and carry current
  • Can't conduct electricity when solid because the ions are fixed in place
• Substances that consist of small molecules

  • They don't conduct electricity because small molecules do not have an overall electric charge
• Polymers


  Have very large molecules
• Substances that consist of small molecules

  • Are usually gases or liquids
  • Have low boiling and melting points
• Giant Covalent Structures


  Substances that consist of giant covalent structures are solids with very high melting points
• Atoms in polymer molecules


  • Linked to other atoms by strong covalent bonds
• Intermolecular forces between polymer molecules

  • Relatively strong
• Polymer substances

  • Solids at room temperature
• Giant Covalent Structures


  • 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