Final answer:
The relationship between electronegativity and atomic size is inverse; electronegativity decreases as atomic size increases. This trend is due to the nucleus's reduced ability to attract electrons when they are further away, as seen within groups on the periodic table.
Step-by-step explanation:
The relationship between electronegativity and the size of an atom is an inverse one. Electronegativity is defined as the ability of an atom to attract electrons to itself, and this is affected by the atom's size among other factors. Typically, as the size of an atom increases, its ability to attract electrons decreases, this is because the further the electrons are from the nucleus, the less attraction the nucleus can exert on them.
Looking at the periodic table, the size of atoms increases as you move from the top to the bottom of a column (also called a group). For instance, for halogens: F, Cl, Br, I, the size varies in the order F < Cl < Br < I, with fluorine being the smallest and iodine being the largest. Correspondingly, their electronegativities decrease in the order F (EN 3.98) > Cl (EN 3.16) > Br (EN 2.69) > I (EN 2.66), with fluorine being the most electronegative.
The periodic trend in electronegativity shows that electronegativity generally increases across a period (from left to right) as the atomic size decreases, improving the nucleus' effective pull on bonding electrons. Conversely, electronegativity decreases down a group (from top to bottom) as the atomic size increases, diminishing the nucleus' pull on bonding electrons.