Atomic radius decrease across the period from left to right because in moving from left to right the nuclear charge increase but the number of electrons remains the same... this unusual disturbances make electrons come closer to the nucleus due to the reason that more protons are present in nucleus of atom as compared to the no of electrons . So attraction occurs between two and thus causes the atomic radius to decrease as going from left to right
Atomic radii is the measure of the size of its atoms, usually the mean distance from the centre of the nucleus to the boundary of the surrounding shells of electrons.
The elements in the periodic table are arranged in order of increasing atomic numbers. The horizontal rows are called as periods and vertical columns are called as groups.
The size of an atom decreases as we move across the period because the electrons get added to the same shell and the nuclear charge keeps on increasing. Thus the electrons get more tightly held by the nucleus.
As, the valence electrons come near to the nucleus due to the increased attraction between the nucleus and the shared pair of electrons.
Thus atomic radius decrease from left to right across a period in the periodic table.
