Physical 1

• The model for atomic structure has evolved over time as knowledge and scientific understanding changes
• Plum Pudding Model


  Atoms consisted of a sphere of positive charge with small negative charges distributed evenly within it
• Electron Shell Model


  The atom consists of a small, dense central nucleus surrounded by orbiting electrons in electron shells

  
• The Rutherford scattering experiment discovered the Electron Shell Model


  1911
• The nucleus consists of protons and neutrons giving it an overall positive charge
• The nucleus contains almost the entire mass of the atom
• In a neutral atom, the number of electrons is equal to the number of protons due to the relative charges
• Fundamental particles


  • Proton
  • Neutron
  • Electron
• Relative charge of fundamental particles

  • Proton: +1
  • Neutron: 0
  • Electron: -1
• Relative mass of fundamental particles

  • Proton: 1
  • Neutron: 1
  • Electron: 1/1840

  
• The maximum number of orbiting electrons that can be held by any single shell depends on the number of the shell
• Calculation for maximum electrons in a shell

  2n² where n is the number of the shell
• Each electron shell must fill before the next one can hold any electrons
• Mass number

  Sum of protons and neutrons in an atom
• Atomic number


  Equal to the number of protons in an atom
• Proton number is equal to the atomic number
• Neutron number can be calculated as mass number minus proton number
• Relative atomic mass (Ar)


  The mean mass of an atom of an element, divided by one twelfth of the mean mass of an atom of the carbon-12 isotope

  
• Relative atomic mass takes the relative abundances of the different isotopes of an element into account

  
• Isotopes

  Atoms of the same element with the same atomic number but with a different number of neutrons, resulting in a different mass number
• Neutral atoms of isotopes will react chemically in the same way as their proton number and electron configuration is the same
• The different mass number of isotopes means they have different physical properties
• Isotopes of Hydrogen


  • Hydrogen: 1 proton and 0 neutrons
  • Deuterium: 1 proton and 1 neutron
  • Tritium: 1 proton and 2 neutrons
• Ion


  Formed when an atom loses or gains electrons, meaning it is no longer neutral and will have an overall charge
• Mass Spectrometry


  An analytical technique used to identify different isotopes and find the overall relative atomic mass of an element

  
• Time of Flight (TOF) Mass Spectrometry


  Records the time it takes for ions of each isotope to reach a detector
• Mass Spectrometry Steps

  1. Ionisation

  2. Acceleration

  3. Ion Drift

  4. Detection

  5. Analysis
• Ionisation


  Sample vapourised and injected into mass spectrometer, high voltage causes ionisation
• Acceleration

  Positively charged ions accelerated towards negatively charged detection plate
• Ion Drift

  Ions deflected by magnetic field into curved path
• Detection

  Positive ions hit detection plate, gain electron producing flow of charge

  
• Analysis


  Current values used to produce spectra print-out with relative abundance of each isotope
• A 2+ charged ion may be produced during ionisation
• The mass to charge ratio (m/z) is halved for a 2+ charged ion

  
• Chlorine spectra display a characteristic pattern in a 3:1 ratio for Cl+ ions and a 3:6:9 ratio for Cl2+ ions

  
• Electron Orbitals


  Electrons are held in clouds of negative charge called orbitals
• Types of orbitals


  • s
  • p
  • d
  • f

  
• Each orbital can hold a different number of electrons before the next one is filled
• Maximum electrons in orbitals

  • s-orbital: 2
  • p-orbital: 6
  • d-orbital: 10
• The energy of the orbitals increases from s to d