Chemistry Unit Four

Chemistry Unit Four

1. C4A - Atomic Structure

   • Electrons on the shells
   • Isotopes - any of two or more forms of a chemical element, having the same atomic number, but having different numbers of neutrons.
   • Atomic Number - Number of Protons in an atom
   • Mass number - The number of protons and neutrons in an atom
   • Protons and neutrons in the nucleus
   • Development of atomic theory
     • Dalton's atomic theory
       • All matter is made of atoms
       • Atoms cannot be broken down into anything simpler
       • All the atoms of a particular element are identical to each other and different from the atoms of other elements
       • Atoms are rearranged in a chemical reaction
       • Compounds are formed when two or more different kinds of atoms join together
     • JJ Thomson's discovery of the electron
       • Discovered the electron in 1897. Showed that atom contained smaller pieces
     • Rutherford's nuclear atom
       • In 1911 Ernest Rutherford used experimental evidence to show that an atom must contain a central nucleus.
     • Bohr's electron orbits
       • Used experimental evidence to support the idea that electrons occupy particular orbits or shells around the nucleus of an atom.
     • Geiger and Marsden's experiment
       • A beam of alpha particles was aimed at very thin gold foil and their passage through the foil detected. The scientists expected the alpha particles to pass straight through. However, some of the alpha particles emerged from the foil at different angles and some even came straight back. The scientists realised that the positively charged alpha particles were being repelled and deflected by a tiny concentration of positive charge in the atom.

2. C4B - Ionic Bonding

   • Ionic Bonding - the bond between a metal and non metal atom
     • Metal atoms lose the electron, or electrons, in their highest energy level and become positively charged ions
     • Non-metal atoms gain an electron, or electrons, from another atom to become negatively charged ions
     • Ionic compounds have high melting and boiling points
     • Dot and Cross Model
   • Giant Ionic Lattice
     • Each ion is surrounded by oppositely charged ions held in place by electrostatic attraction and forming an ionic crystal lattice.
       • Keywords Electrostatic attraction
     • The number of ions in an ionic compound is such that the overall charge of a sample of the compound is zero.
       • Key points Overall Change Zero
     • Ions in crystal lattice are very strongly bonded together
     • High temperature is required to separate the particles and melt the crystal.
     • The ions are held strongly in position so they cannot move and carry an electric current.
     • If ionic compound is melted or dissolved in water the ions are then free to move and so the substance can be electrolysed.
   • Making Electricity
     • For an ionic substance to conduct electricity, ions must be free to move so can carry charge from place to place. Ions move when ionic compound is a molten liquid or in solution but not when it is solid.
     • Electrolysis of Molten Sodium Chloride
       • During electrolysis
         • chlorine gas forms at the anode (positive electrode)
           • hydrogen gas forms at the cathode (negative electrode)
             • a solution of sodium hydroxide forms
       • Half Equations
         • anode: 2Cl– – 2e– → Cl2 (oxidation)
         • cathode: 2H+ + 2e– → H2 (reduction).
       • OILRIG - Oxidation is loss (of electrons), Reduction is gain

3. C4C - The periodic table and covalent bonding

   • Covalent Bond - Bond between non-metal atoms, which combine together by sharing electrons

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