Groups:
1. The vertical columns of elements in the modern periodic table are called groups.
2. The group number indicates the number of electrons in the outermost shell of an atom of an element belonging to that group.
3. The elements in the same group show similar chemical properties
periods:
1. The horizontal row of elements in the modern periodic table are called periods.
2. The period number indicates the number of electronic shells present in an atom of an element belonging to that period.
3. The elements in the same period do not show similar properties, but their chemical properties gradually change from left to right in a period.
