Atomic Structure

• Details of the three sub-atomic (fundamental) particles

  • Particle
  • Position
  • Relative Mass
  • Relative Charge
• Lithium (Li) atom


  Atomic number: 3, Atomic symbol: Li, Mass number: 7
• Atomic number (Z)


  Number of protons in the nucleus
• Mass number (A)


  Total number of protons and neutrons in the atom
• Number of neutrons


  A - Z
• Isotopes


  Atoms with the same number of protons, but different numbers of neutrons
• Isotopes


  • Similar chemical properties because they have the same electronic structure
  • Slightly varying physical properties because they have different masses
• Mass spectrometer


  1. Ionisation

  2. Acceleration

  3. Flight Tube

  4. Detection
• Electron impact ionisation


  A vaporised sample is injected at low pressure, an electron gun fires high energy electrons at the sample, this knocks out an outer electron, forming positive ions with different charges
• Electrospray ionisation


  The sample is dissolved in a volatile, polar solvent, injected through a fine needle giving a fine mist or aerosol, the tip of needle has high voltage, the sample molecule, M, gains a proton, H+, from the solvent forming MH+
• Electron impact is used for elements and substances with low formula mass, can cause larger organic molecules to fragment
• Electrospray ionisation is used preferably for larger organic molecules, the 'softer' conditions of this technique mean fragmentation does not occur
• Acceleration


  Positive ions are accelerated by an electric field to a constant kinetic energy
• Flight Tube


  The positive ions with smaller m/z values will have the same kinetic energy as those with larger m/z and will move faster, the heavier particles take longer to move through the drift area, the ions are distinguished by different flight times
• Detection


  The ions reach the detector and generate a small current, which is fed to a computer for analysis, the current is produced by electrons transferring from the detector to the positive ions, the size of the current is proportional to the abundance of the species
• Relative atomic mass (RAM)

  Weighted average of all the isotopes, calculated as (isotopic mass x % abundance) / 100
• Diatomic molecules like Cl2 and Br2 give characteristic mass spectra patterns
• Molecular ion


  The peak with the largest m/z, due to the complete molecule, equal to the relative molecular mass (Mr) of the molecule
• Electrospray ionisation of molecules

  Gives a peak for the MH+ ion, so to get the Mr of the molecule, 1 must be subtracted from the m/z value
• Models of the atom

  • Bohr model
  • A-level model
• 1. level model


  Electrons arranged in principle energy levels, sub-energy levels (s, p, d, f), and orbitals
• Orbitals


  • Represent the mathematical probabilities of finding an electron, have approximate 3D shapes
• Order of filling sub-shells


  • 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p
• Spin diagrams


  Show electrons in orbitals with opposite spins
• Positive ion formation


  Electrons lost from the outermost shell
• Negative ion formation


  Electrons gained
• Calcium electronic configuration


  1s2 2s2 2p6 3s2 3p6 4s2
• Number of main energy levels

  • 2s
  • 2p
  • 1s
• Number of electrons in sub-level

  • 2
  • 6
  • 2
• Spin diagrams


  • An arrow is one electron
  • The arrows going in the opposite direction represents the different spins of the electrons in the orbital
  • Box represents one orbital
• s sublevels


  • Spherical
• p sublevels


  • Shaped like dumbbells
• When filling up sub levels with several orbitals, fill each orbital singly before starting to pair up the electrons
• Positive ion formation


  Electrons are lost from the outermost shell
• Positive ion examples


  • Mg2+ is 1s2 2s2 2p6
  • O2- is 1s2 2s2 2p6
• Electronic configuration of transition metals

  • Sc 1s22s22p63s23p6 4s23d1
  • Ti 1s22s22p63s23p6 4s23d2
  • V 1s22s22p63s23p6 4s23d3
  • Cr 1s22s22p63s23p6 4s13d5
  • Mn 1s22s22p63s23p6 4s23d5
  • Fe 1s22s22p63s23p6 4s23d6
  • Co 1s22s22p63s23p6 4s23d7
  • Ni 1s22s22p63s23p6 4s23d8
  • Cu 1s22s22p63s23p6 4s13d10
  • Zn 1s22s22p63s23p6 4s23d10
• Transition metal ion electronic configurations

  • Sc3+ [Ar] 4s03d0
  • Ti3+ [Ar] 4s03d1
  • V3+ [Ar] 4s03d2
  • Cr3+ [Ar] 4s03d3
  • Mn2+ [Ar] 4s03d5
  • Fe3+ [Ar] 4s03d5
  • Co2+ [Ar] 4s03d7
  • Ni2+ [Ar] 4s03d8
  • Cu2+ [Ar] 4s03d9
  • Zn2+ [Ar] 4s03d10
• When forming ions, lose 4s before 3d
• s block element


  Outer electron is filling a s-sub shell
• p block element


  Outer electron is filling a p-sub shell