Classification of Elements and Periodicity in Properties Test - 3

Mendeleev arranged elements in horizontal rows and vertical columns of a table in order of their increasing atomic weights in such a way that the elements with similar properties occupied the same vertical column or group.This is because properties of elements are reapting after regular interval.

Modern Periodic Law of element may be defined as the Physical and chemical properties of the elements are periodic functions of their atomic numbers.It means, when the elements are arranged in the order of their increasing atomic numbers, it is observed that the elements of similar properties recur at regular intervals or periodically. As a result of this, the elements fall in certain groups and lead to an arrangement called the modern periodic table of elements. It must be noted that elements are arranged in the periodic table in order of atomic numbers because atomic number is the most fundamental property of an element. The systematic arrangement of elements in modern periodic table according their atomic number helps in justification of isotopes of elements at one place.

Mendeleev arranged the elements according to their atomic weights. He corrected the atomic weights of few exisiting elements to explain their chemical and physical behaviour. Moreover, he felt that few elements are still to be discovered, so he left empty spaces for them in his periodic table. Two such elements whose properties he predicted; and were later discovered are Gallium and Germanium respectively.

The Modern periodic  law is stated as  :
" Physical and chemical properties of elements are periodic functions of their atomic numbers. That is the properties of elements will be repeated after regular intervals.

The groups are numbered from 1 to 18; where group 1 is alkali metal group and group 18 is for the noble gases.