1 Atomic structure

1 Atomic structure

1. Sub-atomic particles

   • protons, p
   • neutrons, n
   • electrons, e
     • surround the nucleus
   • nucleons (n + p)
   • arrangement
     • held together by a force
       • strong nuclear force
         • much stronger than electrostatic force

2. Electron shells

   • shell = 2n^2
     • n = number of the shell

3. Atomic number, z

   • # of protons in the nucleus
   • Also called proton number
   • mass number, A
     • # protons + # neutrons in nucleus
     • nucleons
     • Isotopes
       • same # of protons but different number of neutrons

4. Mass spectrometer

   • Most useful instrument for the accurate determination of relative atomic masses
   • Happening?
     • 1. Kept under high vacuum so the ions do not collide with air molecule
     • 2. In gaseous state. If the sample is a solid it is vaporised first.
     • 3. Ionisation
       • A beam of electrons from an 'electron gun' knocks out electrons to form +ve ions
     • 4. Acceleration
       • +ve ions are attracted towards -vely charged plates and are accelerated to a high speed
       • The lighter the ions, the faster they go
       • Some ions pass through slits in the plates and form into a beam
     • 5. Deflection
       • The beam of ions then moves into a magnetic field at right angles
       • The deflection of an ion depends on the ratio of its mass to charge(m/z)
         • z is the charge on the ion (usually 1+)
         • The higher the charge, the stronger it deflects
       • The deflection also depends on the magnetic field
     • 6. Detection
       • Ions strike the detector, accept electrons, lose their charge and create a current which is proportional to the abundance of each ion
   • Neon has an average relative atomic mass of: (90.5 * 20) + (9.2 * 22) / 100 = 20.124

5. Energy levels

   • Divided into sub-levels
     • s
       • 2e
     • p
       • 6e
     • d
       • 10e
     • f
       • 14e

6. Electron arrangements and ionisation energy

   • Ionisation energy
     • Refer to mass spectrometer, happening, 3.
     • Successive ionisation energies
       • 1st IE = Na(g) --- Na+ (g) + e-
       • 2nd IE = Na+ (g) --- Na 2+ (g) + e-
       • 3rd IE = Na 2+ (g) --- Na 3+ (g) + e-
     • Trends
       • Across a period
         • IE generally increase bcoz the nuclear charge is increasing
       • Down a group
         • In 1st IE, decrease bcoz the outer electron is in the main level that gets further from the nucleus
         • Nuclear charge increases

Images and files in the map