unless you are keen to know more about the properties of elements.
please do not read the following post.
You have been warned.
Ionization energy increases across the period. Due to the increase in nuclear charge (1 proton for each element across the period), although the no. of electron shells remains the same. Hence, making the element harder to lose even the most loosely bounded valence electrons due to the positive nuclei pulling stronger on the valence electrons.
Ionization energy decreases down the group. Due to the increasing no. of electron shells down the group, hence making the outermost shell electrons even further away from the nuclei, thus easier to remove down the group.
Also, the presence of increasing no. of "in-between" electrons down the group, causes a replusion effect on the outermost electrons, hence helping outermost electrons move out of the shells even easier.
Electronegativity decreases down the group. Due to increasing no. of eletron shells on elements, which has weaker attraction for the in-bound electrons due to increased distance between the shell and the nuclei. Extra distance weakens the attraction for inbound electrons.
Elements at the bottom also has greater no. of "in-between" electrons, hence causing a great repulsion effect on in-bound electrons, therefore lesser attraction.