chemistry

• Chemical bonding

  Covalent, ionic Metallic Banding and Intermdecular forces
• intermolecular

  Band is a bond between atoms within molecules
• Covalent bonds


  Considered to be intermolecular
• Electronegativity


  A measure of the tendancy of an outan to bading pair of electrons
• Covalent bond


  Sharing of at least one pair of electrons by atoms
• Non-polar (pure) covalent bond


  When the electrons are equally shared due to zero difference in electronegativity
• Polar covalent bond


  When the electrons are unequally shared due to a difference in electronegativity
• The greater the difference in electronegativity the more polar the bond
• Ionic bonding


  Involves a transfer of electrons to form cations and anions which is electrostatically attracted in an ionic crystal lattice
• Ionic bonding is generally between metals and non-metals
• Metallic bonding


  The attraction between positive metal kernels and a sea of delocalized electrons
• Bonding is neither intramolecular nor intermolecular
• Intermolecular forces


  Forces of attraction between molecules or between atoms of noble gases
• Polar molecule (dipole)


  A molecule in which the electrons are unevenly distributed resulting in a + and - end
• Van der Waals forces

  Intermolecular forces
• Types of intermolecular forces

  • London forces (dispersion forces)
  • Dipole-dipole forces
  • Hydrogen bonding (special case of dipole-dipole)
• All interactions between molecules involve London forces
• London forces


  The strength is influenced by the size of the temporary dipoles which is influenced by the number of electrons and the interacting surface area of a molecule
• Asymmetrical molecules


  Considered to be polar
• Symmetrical molecules


  Considered to be non-polar
• Molecular shapes


  • Linear
  • Angular
  • Trigonal
  • Tetrahedral
  • Trigonal bipyramidal
• Intermolecular forces


  Forces of attraction between the particles, keeping the substance in that state
• Intramolecular forces


  Electric forces of attraction between atoms
• Intermolecular forces


  Forces of attraction between molecules or between atoms of noble gases as a result of the sharing or transmission of electrons
• Types of van der Waals forces

  • London forces (dispersion forces)
  • Dipole-dipole forces
  • Hydrogen bonding (special case of dipole-dipole)
• Dipole-dipole forces


  Electrostatic forces of attraction between permanent dipoles in molecules
• Hydrogen bonding


  A special case of dipole-dipole forces, the strongest of all intermolecular forces but still weaker than a covalent bond
• A hydrogen bond is a force of attraction between a hydrogen covalently bonded into a molecule with a small highly electronegative atom N, O or F and a lone pair of electrons of a neighbouring molecule on the N, O or F atom
• Induced dipole forces (London forces or van der Waals dispersion forces)


  The attraction between non-polar molecules or neutral atoms
• Substances that experience induced dipole forces

  • Noble gas atoms (e.g. Ne, He, Ar)
  • Diatomic molecules (e.g. H2, N2, O2, F2, Cl2)
  • Non-polar molecules (e.g. CO2, CH4, CCl4)
• When a substance experiences intermolecular forces


  It affects the melting point, boiling point, and other physical properties
• Ionic solids (e.g. sodium chloride) have high melting points due to the strength of the many electrostatic forces of attraction between the cations and anions in the ionic crystal lattice</b>
• For simple molecular substances, the melting and boiling points are affected by the strength and relative number per molecule of the intermolecular forces
• When comparing melting and boiling points of molecules, the difference is mainly due to London forces, except for those that experience hydrogen bonding
• When comparing melting and boiling points of molecular substances of similar mass in different groups or homologous series, the difference is due to the presence of other intermolecular forces besides London forces
• When comparing melting and boiling points of molecular substances that involve hydrogen bonding, the difference is due to the relative number of hydrogen bonds per molecule
• Electrical conductivity


  Metals and graphite conduct electricity due to the presence of delocalized valence electrons, while ionic compounds only conduct when molten or in aqueous solution when the ions are free
• Exothermic reaction


  A reaction which transforms chemical potential energy into thermal energy
• Endothermic reaction


  A reaction which transforms thermal energy into chemical potential energy
• Bond breaking absorbs energy and bond formation releases energy, with stronger bonds requiring more energy to break and releasing more energy when formed