When graphing electronegativity vs. atomic number, why are the halogens the peaks and noble gases valleys?

When you graph electronegativity vs. the atomic number, the halogens starting with fluorine until Iodine are the peaks or highest points. The noble gases are the valleys or lowest points. Can anyone answer this question, I know it deals with either the nucleus being largest and having greater attraction or the nucleus being smaller and having less attraction.