Atomic Structure

Atomic Structure

1. Fundamental Particles that compose atoms

   • Protons
     • Found in nucleus
     • relative mass = 1
     • Relative charge = +1
   • Neutrons
     • Found in nucleus
     • Relative mass =1
     • Relative charge = 0
   • Electrons
     • Surround the nucleus
     • Relative mass = 1/1840
     • Relative Charge = -1

2. The arrangement of the electrons

   • Electron shells
     • 1st shell = 2 electrons
     • 2nd shell = 8 electrons
     • 3rd shell = 18 electrons
   • General formula
     • number of electrons in shell = 2n²
   • Electron Diagrams
     • write the number of electrons in each shell,
       • inner shell first
     • Separate numbers with a comma
     • e.g carbon would be 2,4

3. Mass number, atomic number and isotopes

   • Mass Number, A
     • Number of protons + number of neutrons
     • the is because the electrons weigh virtually nothing
   • Atomic Number, Z
     • Equal to the number of protons
     • All atoms of the same element have the same atomic number.
   • Isotopes
     • Atoms with the same number atomic number, but a different mass number
     • i.e they have a different number of neutrons

4. Mass Spectrometry

   • Ionisation
     • beam of electrons knock an electron form the outer shell of the sample
     • This makes them positive ions
   • Acceleration
     • Positive ions are attracted to negatively charge plates
     • Causing the ions to accelerate, the lighter they are the faster they go
     • Deflection
       • beam is moved into a magnetic field at right angle to the direction of travel
       • Deflection depends on the ratio of its mass to charge, heavier ions are deflected less
   • Detection
     • The magnetic field is gradually increased so that the ions enter the detector one after another
     • The ions strike the detector and accept an electron so they are no longer ions