<Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (February 2007) (Learn how and when to remove this template message) </Td> </Tr> <P> A diagonal relationship is said to exist between certain pairs of diagonally adjacent elements in the second and third periods of the periodic table . These pairs (lithium (Li) and magnesium (Mg), beryllium (Be) and aluminium (Al), boron (B) and silicon (Si) etc .) exhibit similar properties; for example, boron and silicon are both semiconductors, forming halides that are hydrolysed in water and have acidic oxides . </P> <P> The organization of elements on the periodic table in to horizontal rows and vertical columns makes certain relationships more apparent (periodic law). Moving rightward and descending the periodic table have opposite effects on atomic radii of isolated atoms . Moving rightward across groups decreases the atomic radii of atoms, while moving down the periods will increase the atomic radii . </P> <P> Similarly, on moving rightward a group, the elements become progressively more covalent, less basic and more electronegative, whereas on moving down a period the elements become more ionic, more basic and less electronegative . Thus, on both descending a period and crossing a group by one element, the changes "cancel" each other out, and elements with similar properties which have similar chemistry are often found--the atomic size, electronegativity, properties of compounds (and so forth) of the diagonal members are similar . </P>

3. give any two similarities between li and mg