Examine other groups and periods in the periodic table to see if the same trends exist. What trends do you see in ionization energy down a group and across a period?
Yes, the same trend exists in other groups. For instance, if we look at groups starting with 8 and greater, we notice that all elements there have valence that is 1 point greater compared to each previous group. And the mass increases as we go down the group.
Trends in ionization energy down a group: it decreases as the nucleus diameter of the atom increases and charge remains the same, which means that it is easier to 'tear' electrons from the atom.
The ionization energy increases across a period because the charge of nucleus increases and stronger electric forces bond electrons and nucleus.