The elements are classified in two major ways relative to their positions in the periodic table and, as a result, relative to their electrionic configurations and properties. Every element is either a representative element or a transition element. Also, every element is either a metal, a semiconducting element, or a nonmetal.

 

• Representative elements: s or p subshells filling.

 

• Transition elements: d or f subshells filling.

 

• Zn, Cd & Hg fall in the periodic table within the d block and are in a sense the last of the d-transition series. However, in their configurations and properties they are most like representative elements (each has a completely filled d subshell together with a complete s subshell of the next higher energy level) and so we include them in this category.

   

The groups of representative elements in the s and p blocks are given Roman numerals, starting at the left in the periodic table with I for Li - Fr (hydrogen stands alone and is not a member of any group).

Other alternative representations call Be - Ra Group IIA and the transition element families Group IIB.

Very recently, every Group across the table (including the transition elements) have been given a Group number making the chalcogens and halogens Group XVI and Group XVII respectively.

Additional names in the transition elements include:

• Rare earth elements Sc, Y, La - Lu
• Lanthanides Ce - Lu
• Actinides Th - Lr
• Transuranium elements Np, Pu, Am .....

Elements with each of four basic types of electron configurations fall together in the periodic table;

Representative element configuration: Outer configurations vary from ns¹ to ns² np⁵ with all occupied subshells in lower energy levels filled to capacity.

Noble gas configuration: All of the subshells that are occupied by electrons are completely filled. He has the 1s² configuration. All other noble gases have an outer configuration of ns² np⁶, where n indicates the outer energy level.

d-Transition element configuration: The d subshell in the energy level just below the outermost energy level (the n - 1 level) is being filled by electrons. Atoms of these elements generally have the outer configurations (n - 1) d ^1-10 ns^1-2, with all outer subshells that are occupied filled to capacity.

f-Transition element configuration: The f-subshell in the n - 2 level is being filled. In atoms of such elements, the outer configurations are (n - 2) f ^0-14 (n - 1) d ^0-2 ns² with all other subshells that are occupied completely filled.

In appearence the seven semiconducting elements resemble metals. However, in chemical behaviour and in their compounds they are more like nonmetals.

Information provided by: http://www.bpx.cov.ac.uk