Atomic structure, elements,compounds and mixtures

Atomic structure, elements,compounds and mixtures

1. Atoms

   • The smallest part of an element that can exist
   • Atomic structure
     • Electrons surround the nucleus containing neutrons and proton sin energy shells
     • The sum of protons and neutrons in an atom is its mass number
     • Most of the mass of an atom is in the nucleus
   • History of the atom
     • JJ Thompson 1897
       • Discovered the electron and developed the ‘plum pudding model’
         • The atom as a ball of positive charge with electrons stuck in it
     • Ernest Rutherford 1909
       • Rutherford and Marsdon conducted alpha particle scattering experiments
         • Rutherford came up with the nuclear model - positively charged nucleus at the centre and a ‘cloud’ of electrons surround it
     • Neil’s Bohr 1922
       • Electrons orbit the nucleus in fixed shells and aren’t anywhere in between
         • Each Shell a fixed distance from the nucleus and the outer shells have more electrons than the inner shells
     • Rutherford and others 1920s
       • Discovered protons
     • James Chadwick 1932
       • Neutrons
   • Atoms of the same element can have different numbers of neutrons - iostopes

2. Elemensts

   • A substance comprising of only one type of atom

3. Compounds

   • Formed from elements by chemical reactions
   • Compounds contain two or more elements chemically combines in fixed proportions and can be represented by formulas using the symbols of the atoms

4. Mixtures

   • Made up of separate substances which aren’t joined together by chemical bonds
   • The chemical properties of each substance remain unchanges
   • Can be separated by physical methods
   • Methods of separatin
     • Filtration
       • To separate solid particles from a liquid or solution
         • Insoluble solid and a liquid
       • Can be done at atmospheric pressure or reduced pressure (using a water pump)
     • Distillation
       • To separate a liquid from a mixture
         • Used in industry to get pure water from salt water
       • Can be used to separate substances with boiling points significantly far apart
       • Mixture heated so one component evaporates - passes into a condenser and is collected as a liquid
     • Fractional distillation
       • Separating mixtures of different liquids when their boiling points are close together
         • Used for separating crude oil into different groups
       • Has a column - increase the temperature when one liquid has been collected
     • Crystallisation
       • Separating soluble solids
     • Chromatography
       • Used to separate mixtures made up of liquids of different colours
     • Sedimentation
       • Insoluble substances and soluble substances
         • Insoluble settles at bottom of solvent
       • Centrifugation
         • Larger particles further outwards