Electronegativity is a measure of the tendency of an atom to attract or gain an electron.
Atomic size for the reactive elements is based on atomic radii that are based on bonding distances in compounds. The inert gas sizes are determined in a different manner, so are not included. They do show the same vertical trend in size and ionization energy. These effects are summarized in Table 1 below. Similar arguments can be used to explain the trends in ionization energy and electronegativity.