Chemistry Revision

Chemistry Revision

1. Development of the atom

   • John Dalton
     • all matter was made of tiny particles called atoms, which he imagined as tiny solid balls
       • atoms cannot be broken down into anything simpler
       • the atoms of a given element are identical to each other
       • the atoms of different elements are different from one another
       • during chemical reactions atoms rearrange to make different substances
     • Dalton’s model (1803)
   • Democritus
     • (460-370 BCE)
     • Said that tiny, indivisible things make up the world around us
   • J.J.Thompson
     • Thomson’s model (1897)
     • discovered the electron
     • Atoms are neutral overall, so in Thomson’s ‘plum pudding model’
       • atoms are spheres of positive charge
       • electrons are dotted around inside
   • Ernest Rutherford
     • Rutherford's model (1905)
     • Rutherford had discovered the nuclear atom, a small, positively-charged nucleus surrounded by empty space and then a layer of electrons to form the outside of the atom.
   • Niels Henrick David Bohr
     • Bohr’s model (1913)
     • Niels Bohr improved Rutherford’s model. Using mathematical ideas, he showed that electrons occupy shells or energy levels around the nucleus.
   • James Chadwick
     • Chadwick's model(1932)
     • Bohr and other scientists knew that there also had to be a neutral particle the same size as a proton to keep the nucleus stable and to make up the mass
       • Chadwick used a version of Rutherford's experiment, using a sheet of beryllium and a paraffin block instead of gold foil. He was able to prove that a proton-sized neutral particle - now known as the neutron - existed.

2. The History of the Periodic Table

   • John Newlands
     • An English scientist called John Newlands put forward his Law of Octaves in 1864.
       • He arranged all the elements known at the time into a table in order of relative atomic mass.
     • By ordering strictly according to atomic mass, Newlands was forced to put some elements into groups which did not match their chemical properties
       • Metals with non-metals, for example
     • Part of Newland's table of elements
   • Dmitri Mendeleev
     • Dmitri Mendeleev was a Russian chemist, and he published his first periodic table of the elements in 1869
     • Mendeleev's periodic table
     • he arranged the elements in order of increasing atomic weights. He also took into account the properties of the elements and their compounds which caused.
       • showed elements with similar chemical properties lined up in groups

3. Group 1

   • the alkali metals
   • All the Group 1 elements are very reactive
   • Group 1 elements form alkaline solutions when they react with water, which is why they are called alkali metals.
   • The Group 1 elements have similar properties because of the electronic structure of their atoms - they all have one electron in their outer shell.
   • The reactivity of Group 1 elements increases as you go down the group because:
     • the atoms get larger as you go down the group
     • the outer electron gets further from the nucleus as you go down the group
     • the attraction between the nucleus and outer electron gets weaker as you go down the group - so the electron is more easily lost
   • low melting points
   • soft
   • They must be stored under oil to keep air and water away from them.

4. Group 7

   • the halogens
   • Chlorine, bromine and iodine are the three common Group 7 elements
   • Melting and boiling points
   • get less reactive as you go down the group.
   • 7 electrons in outer shell

5. Transition metals

   • They include iron, copper and chromium
   • they conduct electricity in the solid and liquid states
   • they are shiny when freshly cut
   • Compared to group 1
     • higher melting points
     • higher densities
     • greater strength
     • greater hardness
   • Transition elements form ions with different charges
   • They are catalysts

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