5. Electrons and Bonding

• Orbital


  A region around the nucleus that can hold up to two electrons with opposite spins.
• Shells are energy levels, and are given principle quantum numbers.
• Shells


  Groups of atomic orbitals with the same principle quantum number, n.
• The s subshell is spherical
• Each shell from n=1 contains one s-orbital. S-orbitals can contain up to two electrons.
• P-orbitals are dumbbell shaped. Each shell from n=2 contains 3 p-orbitals.
• When forming ion, the highest energy subshell loses or gains electrons. As the 4s sub-shell is at a lower energy than the 3d subshell, it fills first.
• The energies of 4s and 3d are very close together and, once filled, the 3d energy falls below the 4s. This means that 4s sub-shell both fills before the 3d sub-shell and empties before it.
• Configuration of Cr

  [Ar]4s1 3d5.

  This is because it is more stable to have all singularly occupied d-orbitals than to have a half filled subshell.
• Configuration of Cu

  [Ar]4s1 3d10

  A full d-subshell is more stable than a full s-subshell and a partially filled d-subshell.
• Electron repulsions theory


  Electron pair repel each other so that they are arranged as far apart as possible. This arrangement minimises repulsion and holds bonded atoms in a definite shape.
• Ionic bonding

  Electrostatic attraction between positive and negative ions.
• Giant ionic lattices

  • Made up of the same basic unit repeated over and over again.
  • Each ion is electrostatically attracted in all direction to ions of opposite charge.
• Properties of ionic compound

  1. Can conduct electricity when molten or dissolved as the ions in a liquid are mobile and so can carry a charge.
  2. High melting and boiling points. Giant ionic lattices are held together by strong electrostatic forces. It takes a load of energy to overcome these forces.
  3. Ionic compounds are dissolvable in water. Water molecules are attracted to slight positive charges, and pull ions away from the lattice, allowing it to dissolve.
• Covalent bonding


  The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.
• Dative covalent bonding is where both electrons come from one atom.
• Linear molecules


  180, e.g. CO2
• Trigonal planar 


  Molecules have bond angles of 120 degrees.
• Tetrahedral 


  Molecules have bonding angles of 109.5 degrees.
• Trigonal pyramidal bonding has 3 bonded pairs and 1 lone pair. Molecules have a bonding angle of 107 degrees.
• Nonlinear molecules have two lone pairs and a bond angle of 104.5 degrees.
• Electronegativity

  The ability of an atom to attract the bonding electrons in a covalent bond.
• Polar molecules 


  A polar molecule required polar bonds with dipoles that do not cancel out due to direction.
• Permanent dipoles 


  A small difference in charge across a bond resulting from a difference in electronegativity of the bonded atoms.
• Polar molecules


  A molecule with an overall dipole, considering any dipoles across all bonds and the symmetry of the molecule.
• Polar covalent molecule 


  A bond with a permanent dipole.
• Van der Waal's forces

  Both permanent dipole-dipole and induced dipole-dipole forces.
• Permanent dipole-dipole forces

  The attraction between the slightly negative side of a polar molecule and the slightly positive side of another.
• London forces/dispersion forces (IDD)


  As electrons are constantly moving, one electron may be closer to another at any given time. This creates a slightly negative charge momentarily, known as an instantaneous dipole. This will repel electrons in a neighbouring molecule, inducing it to move and create another instantaneous dipole.
• Hydrogen bonding


  A strong dipole-dipole interaction between an electron deficient hydrogen of one molecule and a lone pair of electrons on a highly electronegative atom (FON) on another molecule.
• Relative strengths of IMFs, from highest to lowest:

  1. Hydrogen bonds - involves attraction between a slightly negative lone pair and a slightly positive hydrogen.
  2. Permanent dipole-dipoles - always interacting
  3. Induced dipole-dipole - instantaneous.
• Octahedral molecules have a bonding angle of 90 degrees
• The p subshell has three dumbbell shaped orbitals at right angles to each other.