Topic 1: Atomic Structure and the Periodic Table

Topic 1: Atomic Structure and the Periodic Table

1. Atoms

   • The nucleus contains protons and neutrons
     • Protons have a relative mass of 1 and a charge of +1
     • Neutrons have a relative mass of 1 and a charge of 0
   • Electrons are found around the nucleus, arranged in shells
     • Electrons have a relative mass of 0 and charge of -1
     • The number of protons is EQUAL to the number of electrons
       • Atoms are neutral as charges cancel each other out
   • The atomic number of an element tells you the number of protons (& therefore electrons)
     • The mass number tells you the number of protons + the number of neutrons in the nucleus
       • Number of neutrons = mass number - atomic number

2. Elements

   • An element is a substance made of atoms that all have the same number of protons
     • Contains only one type of atom

3. Isotopes

   • Isotopes are different forms of the same element
     • They all have the same number of PROTONS
     • The number of NEUTRONS chnages
   • The relative atomic mass is an AVERAGE mass of the isotopes that make up an element
     • Relative atomic mass (Ar) = Sum of (isotope abundance x isotope mass number) ------------------------------------- Sum of abundance of all isotopes

4. Compounds

   • Atoms join together to make COMPOUNDS
     • Hard to seperate
   • Compounds are two or more elements chemically bonded together

5. Chromatography

   • 1: draw a line in PENCIL
   • 2: add a spot of ink on to the line and place in solvent
     • Make sure the solvent isn't touching the ink
   • 3: let the solvent travel up the paper, carrying the ink with it
   • 4: each dye will separate as they move at different rates
   • 5: when the solvent is nearly at the top, take the paper out and leave to dry

6. Filtration & Crystallisation

   • Filtration separates insoluble solids from liquids
   • 1: pour solution into evaporating dish
   • 2: heat the solution until most of the solvent has evaporated
   • 3: Remove heat and leave to cool and form crystals
   • 4: dry crystals using filter paper

7. Distillation

   • 1: heat solution
   • 2: as the temperature rises, the component with the lowest boiling point will evaporate
   • 3: the vapour is cooled and condenses and is collected in a separate beaker

8. History of the atom

   • The Plum Pudding Model showed that an atom was a ball of positive charge with negatively charged electrons scattered throughout it
     • Rutherford showed the plum pudding model was inaccurate by carrying out the alpha particle scattering experiment
       • fired positively charged alpha particles at a sheet of gold expecting the particles to pass straight through
         • Most particles went straight through but some were deflected
   • The nuclear model shows that an atom has a positively charged nucleus at the center with a 'cloud' of electrons around it
     • Most of the atom is empty space
     • Alpha particles would pass straight through the empty space unless fired at the nucleus when it would be deflected backwards
     • Bohr's nuclear model showed electrons were arranged in shells which were a fixed distance away from the nucleus which contains protons and neutrons

9. Electronic structure

   • Electrons are arranged in shells (energy levels)
     • !st: 2 electrons 2nd: 8 electrons 3rd: 8 electrons
     • Atoms react to have a full outer shell

10. Metals and non metals

    • metals are found on the left hand side of the periodic table
      • Form positive ions
      • strong
      • Malleable
      • Good conductors
      • High melting/ boiling points
    • Non metals are found on the right hand side of the periodic table
      • Forms negative ions
      • Brittle
      • Dull looking
      • Don't conduct electricity

11. Periodic table

    • Developement
      • Arranged in order of atomic mass
      • Mendeleev placed elements in groups based on their physical and chemical properties
        • He left gaps to allow undiscovered elements with similar properties to be added into the periodic table
    • Modern
      • Arranged in order of increasing atomic number
        • Arranged in groups (vertical) and periods (horizontal)
          • Group number tells you how many electrons are in the element's outer shell
    • Group 1 elements: Alkali metals
      • Soft
      • Reactive
      • As you go down the group
        • Reactivity increaes
          • Melting/ boiling points decrease
      • Forms +1 ions
    • Group 7 elements: Halogens
      • As you go down the group
        • Reactivity decreases
          • Melting/ boiling point increase
      • All halogens are diatomic molecules
        • Fluorine is a poisonous yellow gas
        • Chlorine is a poisonous green gas
        • Bromine is a dense, poisonous red/ brown liquid
        • Iodine is a grey solid or purple vapour
      • Form -1 ions
    • Group 0 elements: Noble gases
      • Inert (unreactive) as they have a full outer shell of electrons
      • As you go down the group
        • Boiling points increase

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