Question

State modern periodic law. What is the number of groups and periods in the modern periodic table?

Answer 1

Hint: Try to recall that in modern periodic tables, there is a periodic recurrence in physical and chemical properties of elements when they are arranged on the basis of their increasing atomic numbers. Now by using this you can easily answer the given question.

Complete step by step solution:
It is known to you atomic that periodic law was first given by Mendeleev who considered atomic mass as the fundamental property for arranging the then known elements in periodic table.
But Henry Moseley interrupted and believed that atomic numbers should be taken into consideration. So, he proposed the modern periodic law.
According to modern periodic law, “the physical and chemical properties of elements are periodic functions of their increasing atomic number”. This means that there is a periodic recurrence in physical and chemical properties of elements when they are arranged on the basis of their increasing atomic numbers.
In modern periodic tables, elements are arranged in increasing order of their atomic number and as a result of this, elements with similar physical and chemical properties fall in certain groups and lead to an arrangement called the modern periodic table of elements.
In modern periodic tables, there are 18 vertical columns called groups and 7 horizontal rows called periods.

Note: It should be remembered to you that the modern periodic law was found successful due to a number of reasons but the most important one was the position of isotopes as they are nuclei with the same atomic number so they were placed under the same elements to which they belong.