Atomic Structures

Atomic Structures

1. Substances

   • Element
     • 1 type of atom
   • Compound
     • 2+ elements chemically combined
   • Mixture
     • 2+ elements/compounds not chemically combined
     • components keep their own properties
     • Separating Mixtures
       • Filtration
         • separate soluble solids from insoluble solids
       • Crystallisation
         • obtain soluble solid from a solution
           • mixtures gently warmed
             • water evaporates leaving pure crystals
       • Simple Distillation
         • obtain a solvent from a solution
       • Fractional Distillation
         • separate mixtures in which components have different boiling points
       • Chromatography
         • separate different soluble, coloured components of a mixture

2. Atoms

   • Thomson
     • 1898 discovered electrons
     • tiny, negative electrons surround by a sea of positive charge
       • plum - pudding model
     • Geiger and Marsden
       • experiment
         • bombarded a thin sheet of gold with alpha particles
           • most positive particles went through atoms, although some bounced back
       • Rutherford
         • looked at results
           • positive charge must be concentrated in small area of atom
             • nucleus
               • nuclear model
         • Bohr
           • electrons must orbit nucleus at specific distance
             • otherwise they would spiral inwards
           • Later Experiments
             • nucleus made of
               • protons
               • neutrons
   • no overall charge
     • equal protons/electrons
   • Isotope
     • same protons, different neutrons
   • Ions
     • metal
       • lose electrons = positive ion
     • non-metal
       • gain electrons = negative ion

3. Periodic Table

   • Group 0
     • noble gases
     • full outer shell of electrons
       • very unreactive non-metals
   • Group 1
     • alkali metals
       • when react become positive
     • 1 electron in outer shell
     • low melting/boiling point that decreases down the group
       • reactivity increase down group
         • outer electron gets further away from nucleus
   • Group 7
     • halogens
       • non-metals
         • when react become negative
     • 7 electrons in outer shell
     • reactivity decreases down group as outer shell gets further away from nucleus
       • less easy to gain an electron
   • Creation
     • Dimitri Mendeleev
       • ordered by increasing atomic number
     • John Newlands
       • 1864
         • 63 elements
           • ordered by atomic weight