Intermolecular Forces

• Definition of electronegativity.

  The ability of an atom to attract the bonding pair of electrons in a covalent bond.
• What is a non-polar bond ?

  The bonding atoms are the same and have the same electronegativity. The bonding electrons are evenly distributed between both atoms.
• Give an example of a non-polar bond.

  H2
• What is a polar bond ?

  Bonded atoms have different electronegativities. The atom with greater electronegativity will attract the bonding electrons more strongly than the other atom. Electrons are unevenly distributed, leading to a small charge seperation called a permanent dipole.
• Name the non-symmetrical shapes ?

  pyramidal and non linear
• Name the symmetrical shapes and the criteria.

  Trigonal Planar

  Linear

  Tetrahedral

  Octahedra

  If all the surrounding atoms are the same
• Are the symmetrical shapes polar or non polar ?

  non polar
• Why are symmetrical molecules non polar ?

  the dipoles of any bonds will cancel out
• What are the three types of intermolecular forces ?

  London forces, Hydrogen bonds and permanent dipole-dipole
• Which intermolecular force occurs in non polar molecules ?

  london forces
• Definition of London forces.

  The uneven distribution of electrons causes a temporary dipole on one molecule. This induces an opposite dipole onto the next molecule. London forces exist between all molecules but are most obvious in non-polar molecules.
• Definition of Permanent dipole-dipole.

  The permanent dipole in one molecule will attract the opposite permanent dipole in a neighbouring molecule resulting in a permanent dipole-dipole force. Dipole-dipole forces exist between polar molecules.
• Definition of Hydrogen bonding.

  The attraction between an electron deficient Hd+ on one molecule and a lone pair of electrons on an F: O: or N: on a different molecule.
• What makes a molecule polar ?

  If it contains polar bonds ANS has a non-symmetrical shape
• What is an intermolecular force ?

  Forces of attraction that occur between simple covalent molecules.
• Rank the intermolecular forces from strongest to weakest.

  Hydrogen bonding

  Permanent dipole-dipole

  London forces
• Does ice or water have a higher density ?

  Water
• Why is ice less dense than water ?

  they hold molecules in a rigid structure with a lot of gaps