Variation of Electronic Configuration in the Groups

Elements within the same group share a similar outer-shell electronic configuration (Table 3.11), and this is really the deeper reason a group's elements share similar properties. The 18 groups collapse naturally into four families, or blocks, based on which type of orbital receives the last ("differentiating") electron.

s-block (Groups 1 and 2). The last electron enters an ns orbital. Group 1 elements are the alkali metals; Group 2 the alkaline earth metals. These are soft metals with low melting and boiling points and low ionisation enthalpies. They are highly reactive, strongly electropositive, form ionic compounds readily, and many impart a characteristic colour to a flame.

p-block (Groups 13-18), the representative elements. General configuration $ns^2\,np^{1-6}$. Group 16 elements are the chalcogens and Group 17 the halogens; Group 18, with the completely filled configuration $ns^2\,np^6$, are the noble (inert) gases. p-block elements have high (strongly negative) electron gain enthalpies and higher ionisation energies than the s-block. They mostly form covalent compounds and frequently show more than one oxidation state. …