A-level Chemistry/Edexcel

The Pattern of Periodic Table - Periodicity

In the periodic table, all elements are arrived in order of increasing relative atomic mass and elements with similar properties recurred at regular intervals. The vertical column of similar elements are called groups and the horizontal row is called period. If there is one outermost electron, that element belongs to Group I. If there are 7, it belongs to Group VII.

In Group 0, the electron structure is -s(square) or -s(square)p(to the power of sixth). Because of their stable electron arrangement, noble gases have large first ionisation energies and exist as monatomic molecules. They have very low melting points and very low boiling points. The melting point increases down the column. The melting point of Helium is the lowest (3K), the 'highest' melting point of noble gases is (211K).

Group I and Group II - Alkali and Alkaline-Earth Metals The chemical properties in Group I and II metals are very similar. There are one / two s-electrons, which are held weakly by the positive nucleus. The atoms readily lose the outermost electrons and form positively charged ions.

e.g. Na = Na+ + e-

e.g. Mg = Mg2+ + 2e-

The first ionisation energy is lower than the second, as the number of shells increases, the distance between the nucleus and the electrons increases, thus the force that held the atoms and nucleus together decreases. They can form ionic bond with Group VI / VII elements and metallic structure. In metallic structure, a 'sea' of electrons between each atom held them together. This arrangement allow the atoms to 'slide' above one another without breaking the bonds. It explains the electrical and thermal conductivity of Group I and II metals.