Chapter 5 - Electrons and Bonding

• Shells:

  • Shells are regarded as energy levels
  • The energy increases as the shell number increases
  • The energy level number is called the principal quantum number n
  • Shells are made up of atomic orbitals
• An atomic orbital is a region around the nucleus that can hold up to two electrons with opposite spins
• Spin: Electrons are orbiting in different directions
• s-orbitals

  • Shape: Sphere
  • Each shell contains one s-orbital
  • The greater the shell number n, the greater the radius of its s-orbital
• p-orbitals

  • Shape: Dumb-bell
  • Each shell (from n=2) contains three p-orbitals
  • The greater the shell number n, the further the p-orbitals from the nucleus
• d-orbitals

  • Each shell (from n=3) contains 5 d-orbitals
• f-orbitals

  • Each shell (from n=4) contains 7 f-orbitals
• Filling of orbitals

  • Orbitals fill in order of increasing energy
  • 1s -> 2s -> 2p -> 3s -> 3p -> 4s -> 3d
  • 4s subshell is lower in energy than 3d subshell so actually fills first
• Filling of sub shells

  • Atomic orbitals within a subshell are of equal energy
  • They fill singly before pairing up
• 1. Fill the orbital's in order of increasing energy
  2. When there are more than one orbital of the same energy, these orbital's are first occupied singly by electrons
  3. Each orbital can hold a maximum of two electrons
• The periodic table is arranged into four blocks.

  The highest energy occupied orbital for an atom determines the block of the periodic table
• Ionic bonding is the electrostatic attraction between positive and negative ions
• Ionic compounds have a giant ionic lattice structure
• Ionic compounds have a high melting and boiling point due to the strong electrostatic attraction between oppositely charged ions. Lots of energy is required to break these strong ionic bonds
• Most ionic compounds are soluble in polar solvents

  Soluble: Dissolves

  Polar: Partially charged molecule like water
• Ionic compounds dissolve in polar solvents

  Ionic compounds will dissolve if:

  • The ionic lattice can be broken down
  • Water molecules are attracted and surround the ions
• Ionic compounds do not conduct electricity when solid, as Ions can’t move
• Ionic compounds do conduct electricity when molten or dissolved because Ions can move
• Covalent bonds: The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
• A covalent bond is the overlap of atomic orbitals, each containing one electron, to give a shared pair of electrons