Diagonal relationship

Diagonal relationship in the periodic table is called the similarity of the properties of several elements in the periodic table of elements. Diagonal relationship because the items in question are inclined to each other, respectively. This relationship relates to two elements of the second and third period. These are lithium and magnesium, beryllium and aluminum, as well as boron and silicon. Between carbon and phosphorus can determine some similarities, and therefore is referred to also as an inorganic phosphorus carbon.

The similarities show up mainly in the types and properties of the compounds formed of an element. So both magnesium and lithium are a large number of organometallic compounds with covalent bonds that have many similar properties. In comparison, sodium forms, the standing directly under the element lithium, strongly built ionic organometallic compounds.

Stronger than with lithium and magnesium are the similarities between beryllium and aluminum. The compounds of these two elements to many non-metals, the hydrides, oxides and chlorides, have very similar properties. Thus, both hydrogen compounds are covalently constructed and polymeric. Magnesium is ionic in comparison.

The similarities of phosphorus to carbon are eg evident in the tendency to multiple bonds and aromatic rings. An ion isolobal to cyclopentadienyl anion is the P5 - ion. From the silicon compounds are not known yet.

The reason for this similarity is the similar value of the ratio of the ionic radius and the positive charge of the nucleus. By occupying another electron shell, there is an increase in the atomic radius, however (which leads to the increase of the effective nuclear charge by which the electrons are more strongly attracted to the nucleus ) by the increase in the nuclear charge being compensated by the value 1.