2.2.1, 2.2.2- Electron Structure, Bonding & Structure

• Atomic Orbitals

  A region around the nucleus that can hold up to two electrons with opposite spins.
• s- orbitals: spherical shaped
• p- orbitals: dumbbell shaped
• No. of electron pairs in orbitals

  s : 1

  p : 3

  d : 5

  f : 7
• Ionic bonding

  Electrostatic attraction between positive and negative ions
• Giant ionic lattices: Oppositely charged ions strongly attracted in all directions
• High melting and boiling points

  Requires more energy to overcome strong forces of electrostatic attraction.
• Electrical conductivity

  Solid: No free mobile electrons; ions held in place by strong electrostatic forces of attraction

  Molten: Ions are free to move; free mobile charge carriers.

  Aqueous: Ions disassociate in water; free mobile charge carriers.
• Covalent bonds

  Strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atom.
• Single covalent bonding: 2 atoms contribute to and share a pair of electrons
• Multiple covalent bonding: Atoms contribute and share multiple pairs of electrons between them
• Dative covalent (coordinate) bonding: A bond in which one atom singly shares all electrons with another atom
• Average bond Enthalphy: The mean energy required to break 1 mole of bonds in gaseous molecules.

  • A measurement of covalent bond strength
• Bond angles

  Trigonal planar: 120

  Tetrahedral: 109.5

  Trigonal bipyramidal:

  • Axial: 90
  • Equatorial: 120

  Octahedral: 90
• Electronegativity

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

  Within molecules containing covalently-bonded atoms with different electronegativities
• Polar molecules require polar bonds with dipoles that do not cancel due to their direction.
• Permanent and induced dipole-dipole forces can both be referred to as Van Der Waal‘s forces.
• Induced dipole-dipole forces = London Dispersion Forces
• Hydrogen bonding

  Intermolecular bonding between molecules containing N. O or F and the H atom of -NH, -OH, or HF.
• Electronegativity

  Ability of an atom to attract bonding electrons in a covalent bond.

  • Increases to F in the periodic table
• Electron Pair Repulsion Theory

  Pairs of electrons around a nucleus repel each other so the shape that a molecule adopts has the electrons positioned as far apart as possible.

  • Strength of Repulsion
  • LP - LP -> LP - BP -> BP - BP
• Orbitals are filled in order of increasing energy, with orbitals of the same energy occupied singly before pairing.
• Energy level

  The shell that an electron is in.
• Shell

  The orbit that an orbital is in around the nucleus of an atom.
• Permanent Dipole

  A permanent uneven distribution of charge
• Polar bond

  A covalent bond that has a permanent dipole due to the different electronegativities of the atoms that make up the bond.
• Non-linear (bent)

  Central atom has 2 bonding pairs and 2 lone pairs
• Octahedral

  Central atom has 6 bonding pairs.
• London (Dispersion) Forces

  Induced dipole-dipole interactions caused when the random movement of electrons creates a temporary dipole in one molecule inducing a dipole in a neighbouring molecule.
• Macroscopic Properties

  Properties of a bulk material rather than the individual; atoms/molecules that make up the material
• Polar Molecule

  A molecule that contains polar bonds with dipoles that do not cancel out due to their direction (asymmetrical)
• Pyramidal

  Central atom has 3 bonding pairs and 1 lone pair
• Simple Molecular Lattice

  Solid structure made of covalently bonded molecules attracted by intermolecular force.
• Tetrahedral

  Central atom has 4 bonding pairs
• Trigonal bipyramidal

  Central atom has 5 bonding pairs.
• Trigonal Planar

  Central atom has 3 bonding pairs
• Strength of metallic bonds

  • directly proportional to the number of delocalised electrons
  • Inversely proportional to the radius of the atoms.
• Boiling points are based on strength of van der Waals’ interactions.

  • Affected by the number of electrons


  Greater opportunity for more extensive temporary dipoles.