0What is diagonal relationship in the periodic table? Discuss with reference to lithium, magnesium, beryllium and aluminium?
- 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 (Li) and (Mg), (Be) and (Al), (B) and (Si) etc.) exhibit similar properties; for example, boron and silicon are both semiconductors forming halides that are hydrolysed in water and have acidic oxides.
- Such relationship occurs because crossing rightward and descending the periodic table have opposite effects.
- On moving rightward a period of the periodic table, the size of atoms decreases, and on moving down a group the size of the atoms increases.
- Similarly, on moving rightward a period, the elements become progressively more covalent, less basic and more electronegative, whereas on moving down the group the elements become more ionic, more basic and less electronegative.
- Thus, on both descending a group and crossing the period 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.
