Explain why the atomic radius of elements decreases as you move across the periodic table from the left to the right

Periodicity:As you move across the row the atomic number increases, ie an additional proton is added for each additional element, this is what makes them different elements rather than isotopes of the same element (as they would be if you were adding neutrons). The electrons in the outer shell have a negative charge and as such are attracted to the positively charged nucleus. As yo u add protons to the nucleus the positive charge at the nucleus gets larger and attracts the outer electrons more strongly, decreasing the atomic radius, therefore as you move across a row the atomic radius decreases.