Group number:
The Group
number of an element is equal to the number of electrons in the valence shell
of an atom of the element.
Example:
- Atomic number of Sodium = 11
- Electronic configuration of Sodium = 2, 8, 1
- Group number of Sodium = 1
- Atomic number of Chlorine = 17
- Electronic configuration of Chlorine = 2, 8, 7
- Group number of Chlorine = 7
Groups form
vertical columns of the Periodic table, starting from 1, and increasing to 8 on
the right.
Period number:
The Period
number of an element is equal to the number of shells required by the electrons
of its atom for electronic configuration.
Example:
- Atomic number of Sodium = 11
- Electronic configuration of Sodium = 2, 8, 1
- Period number of Sodium = 3
- Atomic number of Potassium = 19
- Electronic configuration of Potassium = 2, 8, 8, 1
- Group number of Potassium = 4
Periods form
horizontal rows of the Periodic table, starting from 1 and increasing from top to
bottom.
