Hello everyone. I am currently studying the periodic trends in my chemistry I class. So I just want to make sure I understand the concepts. Z effective= Atomic # - # of core electrons. Z increases across a row and doesn't really change going down a group. Size, radius, of atoms the radius decrease from left to right and increase going down a group. Ionization energies Increases from left to right and from bottom to top of a group electron affinity becomes increasingly negative going from left to right and doesn't really change going down a group but can become increasingly negative going up a group Reactivity decreases going from left to right since ionization energies increase going left to right and increases going down a group since ionization energies decrease going down a group.