1. Number of electrons in outermost shell:
The number of electrons present in the outermost shells does not change on moving down in a group, i.e remains the same.
Hence, the valency also remains same within a group.
2. Number of shells:
In going down a group the number of shells increases by one at each step and ultimately becomes equal to the period number to which the element belongs.
3. Valency:
The valencies of all the elements of the same group are the same. The valency of an element with respect to oxygen is same in a group.
4. Metallic character:
The metallic character of the elements increases in moving from top to bottom in a group.