Provide an example of the diagonal relationship and periodic trends.

The diagonal relationship is the similarity in properties between elements in different periods and groups.

The diagonal relationship is observed between elements that are diagonally placed in the periodic table. For example, lithium (Li) and magnesium (Mg) are diagonally placed in the second period and third group, respectively. They share similar properties such as small size, high electronegativity, and the ability to form stable compounds with similar anions. This is because they have similar effective nuclear charges and electron configurations.

Periodic trends are the patterns observed in the properties of elements as they move across a period or down a group in the periodic table. For example, the atomic radius decreases across a period due to increased effective nuclear charge, while it increases down a group due to the addition of new energy levels.

The diagonal relationship affects periodic trends as it can lead to deviations from the expected trends. For example, the atomic radius of beryllium (Be) is smaller than that of boron (B) despite being in the same period. This is due to the diagonal relationship between Be and aluminium (Al), which causes Be to have a higher effective nuclear charge than expected.

In conclusion, the diagonal relationship and periodic trends are closely related as the former can affect the latter. Understanding these concepts is important in predicting the properties and behaviour of elements.