Final answer:
The periodic law states that element properties are periodic functions of their atomic numbers, reflected in the periodic table arrangement by groups and periods.
Step-by-step explanation:
The main idea of the periodic law is that elements are arranged in the periodic table in order of increasing atomic number, and there exists a periodic pattern in their chemical and physical properties. This concept is fundamental to the structure of the periodic table, where elements with similar properties are found in the same vertical column, known as groups. The periodic law also implies that the arrangement of the elements reflects the recurring trends in their properties, especially when you look at elements sorted in rows, known as periods, and these trends can be used to predict the behavior of the elements in various chemical reactions.