The number of valence electrons in the elements increases incrementally from left to right. The elements of the same period have different valencies. The atomic radii decrease while going from left to right in a period. Metallic character reduces while going from left to right in a period. Chemical reactivity is highest at the two extremes and is the lowest in the centre.
Oxides formed of elements on the left are basic and of elements on the right are acidic in nature.
Oxides of elements in the centre are amphoteric. The superscripted number shows the maximum number of electrons that can be accommodated in that particular orbital.