Bonding

• Ionic bonding


  Occurs between a metal and a non-metal, electrons are transferred from the metal to the non-metal to achieve full outer shells
• Ions


  Charged particles formed when electrons are transferred
• Ionic lattice


  Oppositely charged ions attract through electrostatic forces to form a giant ionic lattice
• Covalent bonding


  Occurs between two non-metals, electrons are shared between the two outer shells in order to achieve a full outer shell
• Multiple covalent bonds


  Multiple electron pairs can be shared to produce multiple covalent bonds
• Dot and cross diagrams


  Used to represent the shared electron pairs in covalent bonds

  
• Dative bonding


  Occurs when both of the electrons in the shared pair are supplied from a single atom, indicated using an arrow from the lone electron pair
• Metallic bonding


  Consists of a lattice of positively charged ions surrounded by a 'sea' of delocalised electrons, producing a strong electrostatic force of attraction
• The greater the charge on the positive ion


  The stronger the attractive force as more electrons are released into the 'sea'
• Ions that are larger in size

  Produce a weaker attraction due to their greater atomic radius
• Physical properties


  Include the boiling point, melting point, solubility and conductivity, and are different depending on the type of bonding and the crystal structure
• Main types of crystal structure

  • Ionic
  • Metallic
  • Simple molecular
  • Macromolecular
• Ionic crystal structure


  • High melting and boiling point, can conduct electricity when molten or in solution, brittle
• Metallic structure


  • Good conductors, malleable, high melting points, nearly always solid at room temperature
• Simple molecular structure


  • Consist of covalently bonded molecules held together with weak van der waals forces, have low melting and boiling points, very poor conductors
• Macromolecular structure


  • Covalently bonded into a giant lattice structure, have very high melting points, rigid
• Electron pairs


  Determine the shape of a molecule, each pair naturally repels each other so that the largest bond angle possible exists between the covalent bonds

  
• Lone pair repulsion


  Lone pairs provide additional repulsive forces, reducing the bond angle between covalent bonds by 2.5 degrees for every lone pair present
• Common molecule shapes


  • Linear
  • V-shaped
  • Trigonal planar
  • Triangular pyramid
  • Tetrahedral
  • Trigonal bipyramid
  • Octahedral
• Electronegativity


  The power of an atom to attract negative charge towards itself within a covalent bond, increases along a period and decreases down a group
• Permanent dipole


  Formed when the two atoms in a covalent bond have different electronegativities, the more electronegative atom draws more of the negative charge towards itself
• Induced dipole


  Can form when the electron orbitals around a molecule are influenced by another charged particle
• Van der Waals forces

  The weakest type of intermolecular force, acts as an induced dipole between molecules
• The larger the Mr of the molecule


  The stronger the van der waals forces
• Straight chain molecules


  Experience stronger van der waals forces than branched chain molecules as they can line up and pack closer together
• Permanent dipole


  Intermolecular force that acts between molecules with a polar bond, the δ+ and δ- regions attract each other and hold the molecules together in a lattice-like structure
• Hydrogen bonding


  The strongest type of intermolecular force, forms between hydrogen and the three most electronegative atoms: nitrogen, oxygen and fluorine
• Molecules held together with hydrogen bonds

  Have much higher melting and boiling points compared to similar sized molecules without hydrogen bonding