Inorganic chemistry

• Electromagnetic radiation


  Can be described in terms of waves and characterised in terms of wavelength and/or frequency
• Relationship between wavelength and frequency


  c = f λ
• Electromagnetic spectrum


  • Different types of radiation arranged in order of wavelength
• Wavelengths of visible light are normally expressed in nanometres (nm)
• Electromagnetic radiation


  Can be described as a wave (has a wavelength and frequency), and as a particle, and is said to have a dual nature
• Photon


  Particles of electromagnetic radiation
• Photon energy


  Proportional to the frequency of radiation
• Photon energy


  Higher frequency radiation can transfer greater amounts of energy than lower frequency radiation
• Energy of a single photon

  E = hf = hc/λ
• Energy of one mole of photons

  E = Lhf = Lhc/λ
• Energy is often in units of kJ mol-1
• Absorption of energy by atoms

  Electrons within the atoms may be promoted to higher energy levels
• Emission of light energy by atoms

  Excited electrons move from a higher energy level to a lower energy level
• The light energy emitted by an atom produces a spectrum that is made up of a series of lines at discrete (quantised) energy levels
• Each element in a sample produces characteristic absorption and emission spectra
• Absorption spectroscopy


  Electromagnetic radiation is directed at an atomised sample, and radiation is absorbed as electrons are promoted to higher energy levels
• Absorption spectrum


  Produced by measuring how the intensity of absorbed light varies with wavelength
• Emission spectroscopy


  High temperatures are used to excite the electrons within atoms, and as the electrons drop to lower energy levels, photons are emitted
• Emission spectrum


  Produced by measuring the intensity of light emitted at different wavelengths
• Atomic spectroscopy


  The concentration of an element within a sample is related to the intensity of light emitted or absorbed
• The discrete lines observed in atomic spectra can be explained if electrons, like photons, also display the properties of both particles and waves
• Atomic orbitals


  Electrons behave as standing (stationary) waves in an atom, and there are different sizes and shapes of standing wave possible around the nucleus, known as orbitals
• Orbitals can hold a maximum of two electrons
• Types of orbitals


  • s, p, d and f (knowledge of the shape of f orbitals is not required)
• Quantum numbers


  Principal quantum number n, angular momentum quantum number l, magnetic quantum number ml, spin magnetic quantum number ms
• Principles governing electron arrangement in atoms

  • Aufbau principle, Hund's rule, Pauli exclusion principle
• In an isolated atom the orbitals within each subshell are degenerate
• Orbital box notation


  Used to represent the relative energies of orbitals in a multi-electron atom
• Electronic configurations using spectroscopic notation and orbital box notation can be written for elements of atomic numbers 1 to 36
• Periodic table blocks


  s, p, d and f blocks correspond to the outer electronic configurations of the elements within these blocks
• Variation in ionisation energies

  Can be explained in terms of the relative stability of different subshell electronic configurations
• There is a special stability associated with half-filled and full subshells
• VSEPR theory


  Used to predict the shapes of molecules and polyatomic ions
• Determining the number of electron pairs surrounding a central atom

  Take the total number of valence electrons, add one for each atom attached, add an electron for every negative charge, remove an electron for every positive charge, divide by two
• Arrangements of electron pairs around a central atom

  • Linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral
• Electron pair repulsion strength

  Non-bonding pair/non-bonding pair > non-bonding pair/bonding pair > bonding pair/bonding pair
• Transition metals


  Metals with an incomplete d subshell in at least one of their ions
• The filling of the d orbitals follows the aufbau principle, with the exception of chromium and copper atoms
• When atoms from the first row of the transition elements form ions, it is the 4s electrons that are lost first rather than the 3d electrons
• Oxidation number


  The specific oxidation state of an element in a compound