The Periodic table

• In the periodic table the elements are arranged in order if increasing atomic number.
• The lements are arranged in periods and groups.

Period:
• A period is a horizontal raw of elements.
• There are seven periods.
• The period number refers to the number of shells present in an element.

For example: The element carbon and sodium.

Carbon has two shells, therefore it belongs to period two. Like wise sodium has three shells so it belongs to period three.

• First period consists of two elements. They are hydrogen and Helium.
• The second and the third period consists of eight elements.
• The fourth and the fifth period consists of eighteen elements.