Question

How many groups and periods are there in the modern periodic table? How do the atomic size and metallic character of elements vary as we move : (i) down a group and (ii) from left to right in a period.

Answer 1

Modern periodic table:

• The modern or long form of the periodic table is based on the modern periodic law which states that; the physical and chemical properties of the elements are the periodic functions of their atomic numbers.
• The modern periodic table is the present form of the periodic table in which the arrangement of elements is in the increasing order of their atomic numbers.
• There are 18 vertical columns or groups and 7 horizontal rows or periods in the modern periodic table.
• The modern periodic table showing the 18 groups and 7 periods is given as;

Variation of the atomic size of elements:

• The atomic radius of an element is known as a measure of the size of its atoms, which represents the mean distance from the nucleus to the outermost boundary of the surrounding cloud of electrons.
• Atomic radii vary in a predictable manner across the periodic table.
• Down a group: The atomic size and the metallic character of the elements increases accordingly.
• From left to right in a period: The atomic size and the metallic character of elements decrease accordingly.

Variation of metallic character trend:

• Metals are substances that have a tendency to lose electrons.
• Down a group: The metallic character increases on going down to the group due to the lesser nucleus force, the electrons become easier to lose as the atomic radius increases.
• From left to right in a period: The metallic character decreases from left to right as the tendency of atoms for more readily accepting electrons increases by going from left to right on the periodic table.

Hence, there are 18 groups and 7 periods in the modern periodic table. And the atomic size and metallic character of elements increase down a group and decrease from left to right in a period.