What's the basis for the periodic law?

📌 CONCEPT: The periodic law is based on the recurring pattern of properties exhibited by elements when they are arranged in order of their increasing atomic radius and atomic number.

📐 RULE / FORMULA: The periodic law is formulated as 'The properties of elements are periodic functions of their atomic numbers' and 'The elements are arranged in increasing order of their atomic numbers in a periodic table'.

💡 WORKED EXAMPLE: Arrange the given elements - Sodium (Na), Magnesium (Mg), Aluminium (Al), Potassium (K) in order of their increasing atomic radii: Na (186 pm) < Mg (145 pm) < Al (143 pm) < K (227 pm). This arrangement leads to the periodic law as elements with similar properties and electron configurations are placed in the same group of the periodic table.

⚠️ COMMON MISTAKE: Students often confuse the periodic law with the arrangement of elements in increasing order of their atomic weights, which is not the basis of the periodic law.