Topic 2

• Types of bonding


  • Ionic bonding
  • Covalent bonding
  • Metallic bonding
• Ionic bonding


  Bonding between metals and non-metals
• Covalent bonding


  Bonding between non-metallic elements and in compounds of non-metals
• Metallic bonding


  Bonding in metals and alloys
• Positive ions


  Formed by metals
• Negative ions


  Formed by non-metals
• All ions have the same electronic structure - they have a full outer shell of electrons
• Ionic compounds are made up of ions of opposite charge
• Ionic compounds contain a metal part and a non-metal part
• Ionic bond


  Strong forces of attraction between ions of opposite charge
• Electrostatic attraction


  The attraction in an ionic bond
• What happens when sodium reacts with chlorine

  Sodium loses an electron to form a positive ion, chlorine gains an electron to form a negative ion, and an ionic compound (sodium chloride) is formed
• What happens when magnesium reacts with oxygen

  Magnesium loses two electrons to form positive ions, oxygen gains two electrons to form negative ions, and an ionic compound (magnesium oxide) is formed

  
• What happens when calcium reacts with chlorine

  Calcium loses two electrons to form positive ions, chlorine gains one electron to form negative ions, and an ionic compound (calcium chloride) is formed
• Ionic compounds


  • Have a giant lattice structure held together by strong electrostatic forces
  • Are solids at room temperature with high melting and boiling points
  • Conduct electricity when melted or dissolved in water
  • Do not conduct electricity when solid
• Ionic compounds are made up of ions of opposite charges, so we need to combine the formulae of ions to write the formulae of ionic compounds
• Molecular substances


  Made from atoms joined by covalent bonds
• Covalent bond


  A shared pair of electrons
• Many non-metallic elements exist as molecules, as do many compounds containing only non-metal atoms
• Molecular substances

  • Made from tiny molecules not bonded to one another
  • Held together by weak intermolecular forces
  • Have low melting and boiling points as little energy is required to break the intermolecular forces
• The bigger the molecule, the higher the melting and boiling point
• Molecules are electrically neutral and do not conduct electricity
• Molecular formula


  The actual number of atoms in the molecule
• Empirical formula

  The simplest ratio of atoms in the molecule
• The number of covalent bonds formed by an atom is equal to the number of electrons needed to give the atom a noble gas electron structure
• Atoms can form single, double, and triple covalent bonds
• In a dot-cross diagram, only the outer electron shells are shown, and any electrons not involved in bonding must be added to that shell

  
• Polymers


  Long chain molecules made from joining lots of small molecules
• Giant covalent substances


  Made from a large number of atoms joined by covalent bonds in a continuous network
• Examples of giant covalent substances

  • Diamond
  • Graphite
  • Silicon
  • Silicon dioxide
• Giant covalent substances have very high melting and boiling points as many covalent bonds need to be broken
• Most giant covalent substances do not conduct electricity as they do not contain any charged particles capable of carrying charge, except for graphite
• Metallic bond


  The strong electrostatic attraction between the delocalised electrons and the positive nucleus of metal atoms
• Metals


  • Have a high melting and boiling point
  • Can conduct electricity
  • Can conduct heat
  • Are malleable
• Alloy


  A mixture of metals or a metal and another element
• Alloys


  • More useful than pure metals
  • The layers are disrupted by atoms of different size, so they can no longer slide over each other

  
• Nanoparticles


  Particles with at least one dimension less than 100 nanometres
• Nanoparticles can behave differently from the bulk material
• Uses of nanoparticles


  • In fuel cells
  • For drug delivery
  • In sun creams
  • In synthetic skin
  • In cosmetics
  • In clothing
  • In deodorants
  • In electronics
• There are safety concerns about the use of nanoparticles