Electronic configurations among groups

It is possible to explain these trends in terms of the electron configurations of the corresponding atoms. Consider first the increase in radius observed as we move down the table, let us say among the alkali metals (Group 1). All these elements have a single s electron outside a filled level or filled p sublevel. Electrons in these inner levels are much closer to the nucleus than the outer s electron and hence effectively shield it from the positive charge of the nucleus. To a first approximation, each inner electron cancels the charge of one pro-... 

It is important to be able to give the electron configuration for each of the main-group elements. This is most easily done by using the periodic table. If you understand how the table is organized, it is not necessary to memorize the order in which the orbitals fill. Review Fig. 12.28 and Fig. 12.29 to make sure that you understand the correspondence among the orbitals and the periods and groups. 

The monovalent thallium ion, with its relatively large ionic radius (1.50 A for a 6-coordinate ion), has only weak electrostatic interactions with its ligands. The valence-shell electronic configuration of d s with a lone pair makes the covalent interactions weak as well. Overall, the thallium ion is weakly solvated in most solvents, and crystallizes even without any coordinated solvent molecules. Thallium(I) compounds are the most widely explored group among thallium derivatives. The T1+ state is also the most stable ion in aqueous solutions. 

Understanding a trend among the elements enables you to make predictions about the chemical behavior of the elements. These trends in properties of the elements in a group or period can be explained in terms of electron configurations. 

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