electron configuration

• Ionisation


  When atoms lose or gain electrons to form positive and negative ions respectively
• First Ionisation Energy


  The energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions
• Equations of First Ionisation Energies

  • Na (g) → Na+ (g) + e-
  • Li (g) → Li+ (g) + e-
  • He (g) → He+ (g) + e-
• Why Ionisation Energies are Endothermic Reactions

  Negative electrons are held in their electron shells by strong electrostatic forces of attraction with the positively charged nucleus. Therefore, more energy must be supplied than is released in order to destroy this attraction and remove one electron from a gaseous atom.
• Successive Ionisation Energies


  A measure of the amount of energy required to remove each electron in turn
• Equations for Successive Ionisation Energies of Lithium


  • Li (g) → Li+ (g) + e- (1st I.E. = +520 kJmol-1)
  • Li+ (g) → Li2+ (g) + e- (2nd I.E. = +7298 kJmol-1)
  • Li2+ (g) → Li3+ (g) + e- (3rd I.E. = +11815 kJmol-1)
• Factors Affecting Ionisation Energies

  • Atomic Radius
  • Nuclear Charge
  • Electron Shielding
• Atomic Radius


  The larger the atomic radius, the smaller the electrostatic forces of attraction between the nucleus and the outer electron, resulting in a lower ionisation energy
• Nuclear Charge


  The higher the nuclear charge, the larger the electrostatic forces of attraction between the outer electrons and the nucleus, resulting in a higher ionisation energy
• Electron Shielding


  The inner electron shells shield the positive charge of the nucleus from the outermost electrons, reducing the size of the ionisation energy
• As you move down a group, atomic radius increases, number of electron shells increases, electron shielding increases, and nuclear charge increases
• As you move down a group

  First ionisation energy decreases
• As you move across a period, the number of electron shells stays the same, electron shielding stays the same, nuclear charge increases, and atomic radius decreases
• As you move across a period 2 or 3


  First ionisation energy increases overall
• There are slight decreases in first ionisation energy between Be and B, and between N and O, due to changes in s and p sub-shell filling
• Think-Pair-Share


  Do you think it is possible for two electrons in the first shell to swap with two electrons in the second shell? Explain your answer.
• Electron Shells have different energy Levels

  It's not possible for electrons to move between electron shells as each electron shell has a different energy level. The amount of energy required to transfer an electron from one electron shell to another is far too large. As result electrons remain fixed in their original electron shells
• Max Planck developed his 'Quantum theory', which states that energy exists in fixed amounts called quanta


  1900
• Niels Bohr applied Planck's theory to electrons. He proposed that electrons could only exist in fixed energy levels (electron shells)


  1913
• Heisenberg's uncertainty principle


  Its impossible to determine accurately both the momentum and position of the electron simultaneously (more we know about the position, less we know about its momentum)
• Quantum mechanical model of the atom

  We can calculate the probability of finding an electron in a given region of space in the atom
• Principle energy levels


  The main energy levels in atoms
• Principle quantum number (n)


  The number given to each main energy level, where n=1 is the lowest energy level
• Main energy levels

  • 1st Shell (n =1)
  • 2nd Shell (n =2)
  • 3rd Shell (n =3)
  • 4th Shell (n =4)
• Sub levels


  The number of sub levels in each main energy level is equivalent to the principle quantum number (n)
• Number of sub levels in each main energy level

  • 1
  • 2
  • 3
  • 4
• Sub-levels


  Within each sub level are sub shells, which are a collection of atomic orbitals
• Atomic orbitals

  Regions of space around an atomic nucleus where there is high probability of finding an electron
• An atomic orbital can hold a maximum of 2 electrons
• Types of atomic orbitals


  • s
  • p
  • d
  • f
• 1. orbital

  An electron cloud with a spherical shape
• 1. orbital


  An electron cloud with a petal shape, there are 3 separate p-orbitals with different orientations
• You DON'T need to know the shape of the d and f orbitals
• Aufbau principle


  Electrons fill the lowest energy orbital available first
• Pauli exclusion principle


  Any orbital can hold a maximum of 2 electrons and these electrons have opposing spins
• Hund's rule of maximum multiplicity

  When filling orbitals of equal energy (e.g. all the p orbital, or all the d orbitals)electrons fill singly before occupying them in pairs
• The 4s orbital is always filled before the 3d orbital because it has a lower energy level
• Electronic configuration


  A simplified way of showing how the orbitals of an atom are filled
• Electronic configuration examples


  • Sulfur
  • Fluorine
  • Calcium
• For negative ions, add electrons. For positive ions, remove electrons.