Elements of Life

Elements of Life

1. The atom

   • Electrons
     • -1 charge
     • arranged in shells
   • Nucleus
     • contains most of the mass
     • contains protons and neutrons
   • Mass no. - total no. of protons and neutrons in the nucleus
   • Atomic (proton) no. - no. of protons only (equals the no. of electrons)
   • Ions - have different no. of protons and electrons
   • Isotopes - atoms of the same element with different no. of neutrons

2. Nuclear radiation

   • Alpha particles (α)
     • Helium Nuclei
     • Stopped by paper
     • Strongly ionising
     • Slight deflection in electric field
   • Beta particles (β)
     • Electron
     • Stopped by aluminium
     • Moderately ionising
     • Large deflection in electric field
   • Gamma rays (γ)
     • EM wave
     • Stopped by lead
     • Weakly ionising
     • Not deflected in electric field
   • Half life
     • Def: time taken for half the radioactive nuclei to decay
     • Completely random
   • Radioactive isotopes
     • Can be used as tracers
       • Too long - patient could be exposed to radioation for too long - harmful effects
       • Too short - Would have decayed before it is used
     • Used to date items
       • Radiocarbon dating
         • How much of a particular isotope of carbon there is in a plant of animal
           • All living things contain the same amount of carbon-14
             • Plants photosynthesis (absorb CO2 and a small amount of carbon-14)
               • As carbon-14 decay, they're replaced by more carbon-14 from the atmosphere
                 • Animals eat plants

3. Electron shell and atomic spectra

4. Bonding

   • Ionic
   • Covalent
   • Structures

5. Shapes of molecules

6. Period table

7. Group 2

8. Atomic models