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Chapter 18 The Periodic Table
 
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1.

Blocks of similar elements

The Periodic Table can be divided into four blocks of similar elements:

  • Reactive metals in Groups 1 and 2.
  • Ordinary, useful metals including transition metals in the centre of the Periodic Table.
  • Non-metals in Groups 3 to 7 above the steps separating metals from non-metals.
  • Noble gases in Group O.
2.

Electron structures

  • Electrons determine the chemical properties of atoms.
  • Electrons occupy layers or shells at different distances from the nuclei of atoms.
    When these shells are filled, the atoms or ions become stable.
    – The first shell nearest the nucleus is full and stable when it contains two electrons.
    – The second shell is full and stable when it contains eight electrons.
    – The third shell is stable (though not full) when it contains eight electrons.
  • Elements in the same group of the Periodic Table have similar electron structures and this gives them similar properties. For example, lithium atoms have two electrons in the first shell and one in the second. Their electron structure is written as 2,1. Sodium atoms have an electron structure 2,8,1.
    Potassium atoms have an electron structure 2,8,8,1.
3.

The alkali metals in Group 1:

  • Are reactive metals with similar properties.
  • Have lower melting points, lower boiling points, lower densities and are softer than other metals.
  • React rapidly with oxygen in the air to form oxides.
  • Become more reactive with increase in relative atomic mass.
  • All the alkali metal atoms have one electron in their outer shell
    When they react, they lose this outermost electron to form stable ions with filled shells and one positive charge
4.

The halogens in Group 7:

  • Are reactive non-metals with similar properties.
  • Form diatomic molecules
  • Have low melting points and low boiling points.
  • Change from gases with increase in relative atomic mass.
  • Become less reactive with increase in relative atomic mass.
  • All the halogen atoms have seven electrons in their outer shell
    When they react, they try to gain another electron in order to have eight
    electrons in their outermost shell which is far more stable
5.

The noble gases in Group O:

  • Are very unreactive non-metals with similar properties.
  • Form monatomic molecules with one atom (e.g. He, Ne, Ar).
  • Have very low melting points and very low boiling points.
  • Are all gases at room temperature.
  • All the noble gas atoms have stable electron structures with eight electrons in their outer shell, except helium atoms which have a very stable single shell with two electrons.
6.

The transition metals:

  • Have similar properties.
  • Have high melting points, high boiling points and high densities.
  • Are unreactive with cold water.
  • Form more than one stable ion
  • Have coloured compounds.
  • Can act as catalysts both as elements and in their compounds
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